Designing Next-Generation Broiler Systems with Composition or Chemotype-Guided Essential Oils: From Intestinal Ecology to Post-Harvest Meat Preservation

Abstract

Essential oils from rosemary, cinnamon, and clove have attracted interest as alternatives to routine antibiotic use in poultry production. Their potential effects include improving gut health, microbial control, oxidative balance, growth performance, carcass traits, and meat preservation. However, comparing the literature is difficult because terms like “rosemary oil,” “cinnamon oil,” and “clove oil” often refer to preparations that are not chemically or functionally equivalent. These preparations vary by botanical source, chemotype, extraction method, storage, formulation, concentration, and route of exposure. This review argues that poultry outcomes should be interpreted through a chemistry- and route-based framework. Rosemary essential oil is typically rich in monoterpenes. Cinnamon oils may be cinnamaldehyde- or eugenol-dominant, depending on the species and plant organ. Clove oil is generally rich in eugenol but remains compositionally variable. These differences influence antimicrobial potency, anti-virulence activity, redox behavior, sensory impact, and stability. The review further distinguishes between direct antimicrobial injury and growth-independent virulence attenuation. It also separates dietary effects in live birds from postharvest effects on meat. Evidence suggests that dietary supplementation can influence intestinal morphology, inflammatory status, nutrient utilization, and carcass composition. These effects are especially notable when formulations are protected or encapsulated. This review aims to critically evaluate rosemary, cinnamon, and clove essential oils as non-interchangeable interventions in poultry systems. It relates their chemical identity, formulation, and route of exposure to outcomes such as gut health, microbial modulation, performance, and carcass traits.

1. Introduction

Efforts to reduce routine antibiotic use in poultry production have intensified interest in nutritional strategies that support performance, intestinal resilience, and food safety [1]. Essential oils (EOs) are prominent among these approaches because their volatile constituents can influence microbial growth, digestive function, epithelial integrity, inflammatory signaling, and oxidative balance [2,3]. Rosemary, cinnamon, and clove were selected for this review because they are among the most widely studied poultry essential oils, yet they also exemplify the chemical and formulation variability that makes cross-study comparison difficult. They have also been investigated for use after slaughter as components of coatings, films, emulsions, and packaging systems intended to delay deterioration of poultry products. Despite this broad interest, responses remain inconsistent across studies: for example, dietary rosemary oil has been reported to improve carcass yield and oxidative stability in some broiler trials, whereas other studies found no significant effect on breast-meat TBARS or carcass traits [4,5,6].

Rosemary, cinnamon, and clove illustrate this problem through distinct chemical architectures. Rosemary essential oil (REO) is generally rich in monoterpene hydrocarbons and oxygenated monoterpenes. Still, the balance between cineole-, camphor-, α-pinene-, and verbenone-associated profiles varies with genotype, season, environment, and extraction method [7,8]. Cinnamon chemistry is strongly dependent on species and plant organ: bark oils are commonly cinnamaldehyde-rich, whereas leaf oils may be enriched in eugenol, cinnamyl acetate, benzyl benzoate, or mixed phenylpropanoid–terpenoid fractions [9,10]. Clove essential oil (ClEO) is more consistently dominated by eugenol, although variation in eugenyl acetate, sesquiterpenes, extraction, and processing remains biologically relevant [11,12]. These compositional differences are mechanistically relevant. Rosemary monoterpenes act predominantly through hydrophobic partitioning into biological membranes and associated changes in membrane organisation. Cinnamaldehyde combines membrane affinity with the electrophilic reactivity of an α,β-unsaturated aldehyde. Eugenol combines membrane partitioning with the hydrogen-donating capacity of a phenolic hydroxyl group. Oils carrying the same botanical name may consequently differ in antimicrobial spectrum, redox behavior, volatility, chemical stability, pungency, sensory compatibility, and concentration–response profile [2,13,14].

Growth performance, nutrient digestibility, organ weights, carcass yield, cut distribution, and abdominal fat primarily reflect processes occurring during rearing and are therefore most directly relevant to dietary interventions [15]. Growth performance, nutrient utilization, intestinal function, organ development, and carcass composition arise during rearing and are therefore most directly relevant to dietary supplementation, whereas lipid and protein oxidation, microbial spoilage, water loss, color instability, textural changes, and sensory deterioration occur after slaughter in muscle, processed products, product surfaces, and packaging environments [16,17]. Dietary supplementation may alter the bird’s physiological condition and the intrinsic properties of the resulting muscle, as shown in oregano feeding studies that followed meat during storage [18]. In contrast, coatings, films, dipping treatments, nanoemulsions, modified-atmosphere packaging and active packaging are postharvest interventions that act directly on the meat surface, product matrix, package headspace, or immediate storage environment [19,20,21].

Previous poultry reviews have established the potential of phytogenic feed additives and summarised their proposed modes of action. However, a clear separation by chemical identity, formulation, route of exposure, and biological compartment is lacking; in particular, many reviews did not distinguish dietary supplementation from postharvest applications, or free oils from protected formulations, when interpreting outcomes [5,6,22,23]. Cross-study interpretation is further complicated when chemically and biologically distinct interventions—including whole essential oils, plant powders, solvent extracts, purified constituents such as trans-cinnamaldehyde or eugenol, encapsulated preparations, multi-component blends, dietary supplementation, and direct postharvest applications—are evaluated together [24,25,26]. Each study is positioned according to chemical identity and composition, formulation, concentration, route of exposure, biological compartment, challenge status, and measured endpoint [6,26].

As illustrated in Figure 1, this review aims to critically evaluate rosemary, cinnamon, and clove essential oils in poultry. Unlike previous poultry reviews that discuss essential oils or phytogenic feed additives in broader terms, our review specifically integrates chemical identity, chemotype/compositional variation, formulation, and route of exposure into a single interpretive framework. We also distinguish dietary effects in live birds from postharvest effects on meat, and we focus on rosemary, cinnamon, and clove as non-interchangeable models of composition-dependent functionality rather than as a generic essential-oil category. By separating chemically non-equivalent preparations and different biological compartments, the review aims to clarify why results across the poultry literature are often inconsistent and to identify which effects are most reproducible under dietary or postharvest use. This article was conducted as a structured narrative review rather than as a formal PRISMA-based systematic review. Relevant studies were identified through targeted searches of major scientific databases, including Scopus, Web of Science, PubMed/MEDLINE, and Google Scholar, using combinations of terms related to rosemary, cinnamon, and clove essential oils; poultry and broiler production; gut health; intestinal morphology; microbial modulation; performance; carcass traits; meat quality; lipid oxidation; water-holding capacity; drip loss; tenderness; and postharvest preservation. Studies were considered for inclusion when they addressed rosemary-, cinnamon-, or clove-derived interventions in poultry production, poultry meat quality, or closely related food-system and mechanistic contexts. To support interpretation, studies were classified according to botanical source, chemotype or reported composition, extraction method, formulation, dose, route of exposure, storage conditions, biological compartment, and measured endpoint. We evaluated dietary and postharvest applications separately. Studies were excluded from the poultry-specific outcome synthesis when they were not relevant to poultry, did not involve rosemary-, cinnamon-, or clove-based interventions, or lacked sufficient information to interpret the preparation, formulation, or route of exposure. Selected bacterial, non-poultry, and general food-system studies were retained only as complementary mechanistic evidence where they clarified essential-oil composition, antimicrobial mechanisms, antioxidant behavior, formulation effects, or postharvest preservation processes. These studies were not treated as direct evidence for poultry performance, gut health, carcass traits, or poultry meat-quality outcomes. Direct comparison among studies was limited by inconsistent dose expression, formulation reporting, study design, and endpoint selection; therefore, the evidence was interpreted qualitatively rather than pooled quantitatively. Studies were excluded from the poultry-specific outcome synthesis if they were not relevant to poultry, did not involve rosemary, cinnamon, or clove-based interventions, or lacked sufficient information to interpret the preparation, formulation, or route of exposure. However, selected bacterial, non-poultry, and general food-system studies were retained as complementary mechanistic evidence where they clarified essential-oil composition, antimicrobial mechanisms, antioxidant behavior, formulation effects, or postharvest preservation processes. These studies were used only to support biological interpretation and were not treated as direct evidence for poultry performance, gut health, carcass traits, or poultry meat-quality outcomes. Direct comparisons between studies may be limited by inconsistencies in dose expression (e.g., mg/kg feed, mL/kg feed, %, mg/mL, µL/mL, and surface application concentrations).

2. Chemical Identity and Compositional Variation as the Basis of Biological Interpretation

Fundamentally, EOs are volatile, multicomponent mixtures composed predominantly of terpenes, terpenoids, and phenylpropanoids, together with alcohols, phenols, ethers, aldehydes, ketones, and esters [2,27,28]. Their biological activity reflects the combined properties of these constituents rather than the action of a single universally dominant molecule. Interactions among major and minor components can modify antimicrobial potency, redox activity, volatility, sensory intensity, and concentration–response relationships [2,27,29]. An essential oil should therefore be regarded as a chemically defined mixture rather than a uniform botanical ingredient.

Rosemary, cinnamon, and clove oils are increasingly investigated as components of antibiotic-reduction strategies because they may affect intestinal microbial ecology, epithelial integrity, inflammatory regulation, oxidative balance, productive performance, and meat stability [12,30,31]. Nevertheless, descriptions such as “rosemary oil,” “cinnamon oil,” or “clove oil” provide only partial information about the intervention. The preparation administered to the bird or applied to poultry meat depends on botanical species, cultivar, plant organ, developmental stage, geographical origin, agronomic conditions, extraction procedure, storage history, and formulation [11,27,28,29]. Chemical variation may remain substantial even among products carrying the same common or commercial name. Oils obtained from different organs, populations, or chemotypes may differ not only in the concentrations of their major constituents but also in the balance among phenolic, aldehyde, and hydrocarbon fractions. These differences influence membrane partitioning, electrophilic reactivity, hydrogen-donating capacity, volatility, pungency, chemical stability, and antimicrobial spectrum. Apparent disagreement among poultry studies may therefore reflect differences in the preparations tested rather than inconsistent biological responsiveness alone [31,32,33,34]. Formulation can modify exposure without changing botanical origin [26,35]. Emulsification and micro- or nano-encapsulation may improve dispersion, reduce volatilization, protect oxidation-sensitive constituents, mask intense flavors, and alter release within feed, gastrointestinal contents, coatings, or packaging matrices [36,37]. A protected preparation and the corresponding free oil may consequently produce different responses even when both originate from the same production batch. Stronger biological activity in an encapsulated treatment does not, by itself, demonstrate improved absorption or bioavailability [38]. Such conclusions require appropriate measurements of encapsulation efficiency, storage stability, release behavior, plasma or tissue exposure, and the concentration delivered to the relevant biological compartment. Thus, two products sold under the same common name may be chemically non-comparable, and this non-equivalence can materially influence growth performance, gut barrier responses, immunity, oxidative status, microbiota modulation, and meat stability [31,32,33].

Chemotype is one of the organising concepts used to interpret this variability and may be shaped by genotype, plant organ, phenological stage, geography, edaphoclimatic conditions, agronomic management, and extraction technology [39,40,41,42]. Extraction and post-extraction handling further influence chemical identity. Hydrodistillation and steam distillation remain widely used, whereas microwave-assisted extraction, subcritical-water extraction, supercritical CO₂ extraction, and related technologies differ in thermal exposure and selectivity for volatile or thermolabile constituents [40,41,43]. Subsequent exposure to oxygen, light, elevated temperature, or prolonged storage may promote evaporation, oxidation, isomerisation, or hydrolysis. The composition measured immediately after extraction may therefore differ from the profile remaining after storage, feed manufacture, pelleting, gastrointestinal transit, or incorporation into a packaging system.

Understanding the chemical profile and variability of essential oils is crucial for interpreting their effects in poultry systems. Differences in extraction methods, source material, and formulation can significantly alter the concentration and activity of bioactive compounds, thereby influencing outcomes in dietary and postharvest applications. Recognizing these nuances enables more accurate comparisons between studies and better predictions of efficacy in practical settings. The major bioactive constituents reported (

Table 1. Major bioactive compounds identified in rosemary (Rosmarinus officinalis L.), cinnamon (Cinnamomum spp.) and clove (Syzygium aromaticum L.) essential oils, their concentration ranges, biological properties and corresponding references.

Bioactive Compound	Primary Chemical Class	Content in Cinnamon Essential Oil (%) /References/ Plant Part	Content in Cloves Essential Oil (%) /References/ Plant Part	Content in Rosemary Essential Oil (%) /References/ Plant Part	Main Biological Properties /References	Key Biological Activity in Poultry
trans-Cinnam-aldehyde	Phenylpropanoid	84.25% [44]; 77.34% [45]; 68.95% [46]; 4.07% [47]/branch; 1–5% [48]/leaves; 65–80% [48]/bark; 71.5% [49]/bark			Antioxidant [44,45,47,49,50], antimicrobial [45,47,49,50,51], antifungal [49], anti-inflammatory [47], antiparasitic [51]	Growth promoter, modulation of gut microbiota [52]
Eugenol	Phenylpropanoid	4.6% [49]/bark 2.77% [46]/ 70–95% [48]/leaves 5–10% [48]/barks	51.51–46.53% [53]/fruits; 90.6% [54]/flower buds; 78.72% [55]/ Plant; 84.63% [56]; 59.87% [57]/buds		Antioxidant [49,50,57,58,59], antimicrobial [49,50,51,57,58,59], antifungal [49,58,59], anti-inflammatory [58,59], analgesic [58,59], antiparasitic [51,59]	Growth promoter, antioxidant and immune support, strength gut health and protection [60,61]
Eugenyl acetate	Phenylpropanoid		8.74% [55]/plant; 2.64% [53]/flower buds; 2.54% [53]/flower buds; 11.37% [56]		Antioxidant [58], antimicrobial [58], anti-inflammatory [58]
L-bornyl acetate	Monoterpenoid	15.89% [47]/twigs
Cinnamyl acetate	Phenylpropanoid-related compound	4.98% [45] 1.46% [44] 7.44% [46] 42–54% [48]/fruits 41.98% [48]/flowers			Antioxidant, antimicrobial, flavoring agent
1,8-Cineole	Monoterpenoid	1.55% [46] 3.19% [45]		27.15–30.26% [62] 11.30% [63]/leaves 33.08–37.75% [64]/aerial parts 17.79–23.40% [65]	Antioxidant, antimicrobial, anti-inflammatory, expectorant	Growth promoter, antioxidant, immunomodulatory and intestinal-health additive [66]
Camphor	Monoterpenoid	60% [48]/bark		31.90% [63] Leaves 13.55–18.13% [64]/aerial parts	Antimicrobial, antioxidant, anti-inflammatory
β-Pinene	Monoterpene			3.49–5.19% [65]
α-Pinene	Monoterpene	2.60% [45] 1.64% [46] 1.30% [49]/bark		29.80–34.34% [62] 8.58–9.32% [64]/ aerial parts 23–17.76% [65]	Antioxidant [46,49,62,64,65], antimicrobial [46,49,62,64,65], anti-inflammatory [46,62,64]
β-Caryophyllene	Sesquiterpene	6.40% [49] 6.60% [47]/twigs 9–14% [48]/fruits	8.82% [55]/plant 23.58% [57]/buds	3.22–0.63% [65]	Antioxidant [49,57,58,65], anti-inflammatory [47,57,58,65], antimicrobial [47,49,57,58,65], immunomodulatory [58]
Caryophyllene oxide	Sesquiterpenoid	12.98% [47]/twigs 7.20% [48]/flowers			Antioxidant [47], antimicrobial [47]
Linalool	Monoterpenoid	7% [49]/bark 1.38% [46]		0.85–0.84% [65]	Antioxidant [46,49,65], antimicrobial [46,49,65]
Limonene	Monoterpene	1.20% [49]/bark 4.42% [46]		~3% [64]/ Aerial parts 4.18–3.11% [65]	Antioxidant [49,64,65], antimicrobial [49,64,65]
Camphene	Monoterpene			5.07–5.58% [64]/aerial parts 9.99–8.36% [65]	Antioxidant [64,65], antimicrobial [64,65]
Borneol	Monoterpenoid			12.2% [63]/ Leaves 2.39–4.56% [65] 4.08–5.48% [64]/ Aerial parts	Antioxidant [63,64,65], antimicrobial [63,64,65], anti-inflammatory [63,64,65]
Verbenone	Monoterpenoid			7.63–8.14% [62] 2.33–0.30% [65]	Antioxidant [62,65], antimicrobial [62,65]
Geraniol	Monoterpenoid			4.47–5.22% [62]	Antioxidant [62], antimicrobial [62], anti-inflammatory [62]
Myrcene	Monoterpene			10.70% [63]/leaves 2.43–0.05% [65]	Antioxidant [63,65], anti-inflammatory [63,65]
α-Terpineol	Monoterpenoid			6.79–8.17% [64]/ aerial parts 2.30% [65]	Antioxidant [64,65], antimicrobial [64,65]
p-Cymene	Monoterpene	1.90% [49]/bark		2.42–3.11% [64]/aerial parts 4.51–10.91% [65]	Antioxidant [49,64,65], antimicrobial [49,64,65], anti-inflammatory [64,65]
α-Humulene	Sesquiterpene	1.70% [49]/bark	3.74% [57]/buds	1.22% [65]	Antioxidant [49,57,65], anti-inflammatory [58,65], antimicrobial [49,57,65]
δ-Cadinene	Sesquiterpene	1.44% [49]/bark; 4.79% [47]/twigs			Antioxidant [47,49], antimicrobial [49]
α-Selinene	Sesquiterpene		4.67% [57]/buds		Antioxidant [57], antimicrobial [57]
α-Terpinyl acetate	Monoterpenoid		4.12% [57]/buds		Antioxidant [57], antimicrobial [57]
γ-Eudesmol	Sesquiterpenoid	8.03% [47]/twigs			Antioxidant, anti-inflammatory [47]
T-Cadinol	Sesquiterpenoid	5.49% [47]/twigs			Antioxidant [47], antimicrobial [47]
trans-β-Elemenone	Sesquiterpenoid	4.25% [47]/twigs			Antioxidant [47]
Cadalene	Sesquiterpene-derived compound	4.19% [47]/twigs			Antioxidant [47]
Coumarin acid	Phenylpropanoid	1.79% [45]; 6.43% [44]			Anticoagulant [44,45], antioxidant [44,45], anti-inflammatory [44,45]; hepatotoxic at high concentrations

) in rosemary, cinnamon, and clove essential oils further illustrate why chemical identity must be specified rather than inferred from botanical name.

In cinnamon oils, trans-cinnamaldehyde may range widely from approximately 4.07% to 91.09% [44,45,46,47,48,50,51,67,68,69,70,71], reflecting strong species-, organ-, and chemotype-dependent variation. Eugenol is also highly variable, occurring at approximately 4.60–78.00% in cinnamon oils [46,48,50,51,69] and 46.53–90.60% in clove oils [11,53,54,55,56,57,58,59], where it usually represents the dominant phenylpropanoid fraction. Other clove-associated constituents, including eugenyl acetate [54,55], β-caryophyllene [53,54,55,56,59,72], α-humulene [11,46,56,57], α-selinene [56], and α-terpinyl acetate [56], may further modify antimicrobial potency, antioxidant behavior, volatility, sensory intensity, and stability. Cinnamon oils may additionally contain cinnamyl acetate [44,45,48,70], benzyl- or sesquiterpene-associated fractions such as caryophyllene oxide, γ-eudesmol, T-cadinol, trans-β-elemenone, cadalene, δ-cadinene, linalool, geranial, camphor, α-pinene, limonene, p-cymene, α-humulene, and low concentrations of coumarin [14], with each profile implying a different biological exposure. REO is compositionally distinct from both cinnamon and clove because it is dominated mainly by monoterpene hydrocarbons and oxygenated monoterpenes. Reported constituents include 1,8-cineole [62,63,64,65], camphor [65,72,73,74], α-pinene, camphene, borneol, verbenone, geraniol, myrcene, α-terpineol, linalool, limonene, and p-cymene [63,69,75]. These compounds are generally associated with antioxidant, antimicrobial, and anti-inflammatory properties, but their activity depends on their relative abundance and on the surrounding chemical matrix. For example, 1,8-cineole has been reported at approximately 6.40–38.50% in rosemary oil [62,63,74,76,77], camphor at 10.97–31.90% [72,77,78], α-pinene at 7.10–34.34% [72,73,74,77,79], camphene at 4.18–9.60% [77,78], borneol at 4.08–12.20% [77], and verbenone at 7.63–15.44% [64,74]. By contrast, cinnamon and clove oils often contain higher proportions of phenylpropanoids such as cinnamaldehyde and eugenol, which confer stronger electrophilic or phenolic redox characteristics. Therefore, the biological activity of these oils cannot be explained by a single shared “essential oil” effect; rather, it reflects the balance among aldehydic, phenolic, monoterpenoid, and sesquiterpenoid constituents.

Overall, the reported compositional ranges for these compounds indicate that rosemary, cinnamon, and clove essential oils differ not only in their dominant molecules but also in the secondary constituents that shape antimicrobial spectrum, antioxidant capacity, anti-inflammatory potential, sensory profile, and safety considerations [12,14,80]. Trans-cinnamaldehyde, eugenol, cinnamyl acetate, eugenyl acetate, 1,8-cineole, camphor, α-pinene, β-caryophyllene, linalool, borneol, verbenone, p-cymene, α-humulene, and related minor compounds have all been associated with antioxidant and antimicrobial effects [81,82,83,84]. At the same time, some also show antifungal, anti-inflammatory, immunomodulatory, analgesic, antiparasitic, expectorant, or flavoring properties [85,86]. However, the presence of a compound does not guarantee equivalent biological activity across oils, as efficacy depends on concentration, interactions among constituents, formulation, route of exposure, and the biological compartment being targeted [35,87]. This reinforces the need for full compositional reporting in poultry studies, ideally including the major and minor constituents, their percentage ranges, botanical source, plant organ, extraction method, formulation, and storage conditions.

3. Chemical Diversity of Rosemary, Cinnamon, and Clove Essential Oils

3.1. Rosemary Essential Oil (REO): Composition/Chemotype Plasticity and Monoterpene-Rich Composition

Because EOs are chemically heterogeneous and their biological effects depend on chemotype, extraction, storage, and formulation, the next step is to examine each oil separately. REO exemplifies this principle, as its composition is highly variable yet remains broadly monoterpene-rich. The following section, therefore, focuses on rosemary essential oil as a case study of chemotype plasticity and composition-dependent activity in poultry. Rosemary essential oil is a monoterpene-rich volatile fraction commonly containing α-pinene, 1,8-cineole, camphor, borneol, verbenone, camphene, and bornyl acetate [7,8,65,79,88,89,90,91,92,93,94,95,96]. Cluster analyses across the literature and germplasm datasets identify multiple chemotypes, commonly centered on 1,8-cineole, verbenone, camphor, and α-pinene [8,88,89,94]. These profiles are not static. Genotype, domestication status, geography, climate, season, harvest time, organ selection, and extraction technology all alter the relative abundance of major volatiles [7,8,79,88,89,90,91,92,93,94,95]. Leaves, flowers, and mixed aerial tissues may also produce oils with distinct profiles of oxygenated monoterpenes and biological activities [63,79,89].

Extraction can amplify this variation. Hydrodistillation, steam distillation, microwave-assisted recovery, and solvent-based procedures differ in thermal exposure and constituent selectivity [93,94,97]. Seasonal-extraction comparisons have shown that the harvest period and distillation procedure may substantially alter the concentrations of camphor, α-pinene, camphene, and 1,8-cineole, as well as the antioxidant or anti-inflammatory activity measured in the corresponding assay [93]. These findings show that harvest period and extraction procedure can alter both composition and assay response, but they do not establish that oxygenated monoterpene enrichment invariably predicts superior biological activity. Even within a single genotype, harvest timing can drive measurable shifts in the relative abundance of 1,8-cineole, α-pinene, and camphor across monthly and diurnal scales [91,93,98]. Extraction adds a final layer of divergence, as hydrodistillation, steam distillation, microwave-assisted methods, and solvent-based approaches recover different volatile balances and bioactivity patterns. These differences matter because extraction conditions influence not only which constituents are recovered, but also their relative proportions, stability, and downstream biological effects. For example, more heat-intensive methods may favor certain volatiles while promoting losses of more labile compounds, whereas solvent-based or -assisted extraction approaches may recover a chemically distinct profile that is not directly comparable with a conventional distilled oil [8,92,99].

The relationship between rosemary composition and function is therefore conditional. Oils enriched in oxygenated monoterpenes frequently show substantial antimicrobial activity, yet the magnitude of the response depends on the microorganism, concentration, assay system, food or biological matrix, and accompanying constituents [79,89,91,95,97,99]. Most major rosemary volatiles are less effective direct hydrogen donors than phenolic compounds such as eugenol. In vitro, their activity is more closely associated with membrane partitioning, altered permeability, ion imbalance, and context-dependent effects on microbial or host signaling. A strict distinction must also be maintained between REO and non-volatile rosemary extracts. The essential oil is dominated by volatile mono- and sesquiterpenes, whereas many solvent or standardised rosemary extracts contain substantial concentrations of the phenolic diterpenes carnosic acid and carnosol [2,30,31]. These compounds account for much of the strong chain-breaking antioxidant activity conventionally attributed to rosemary extracts, yet they are not representative markers of the distilled volatile fraction. This creates both an opportunity and a challenge: rosemary powder, phenolic extract, free REO, and encapsulated REO offer a range of related botanical preparations that can be tailored to different poultry applications, but they also constitute distinct forms of evidence that cannot be treated as interchangeable. REO therefore illustrates how chemotype, extraction method, and formulation can be leveraged to optimise biological activity, while also highlighting the need for careful standardisation and interpretation [35,80,90]. In live birds, the same balance of opportunity and challenge is even more pronounced for cinnamon, where common-name labelling can obscure major differences in species, plant organ, and dominant chemical constituents [14,100]. The next section therefore turns to cinnamon essential oil as a case study of species- and organ-dependent phenylpropanoid diversity in poultry research.

3.2. Cinnamon (CinEO): Species- and Organ-Dependent Phenylpropanoid Profiles

Cinnamon provides the clearest example of why common-name labelling is chemically insufficient. In feed-additive discourse, “cinnamon” may refer to multiple Cinnamomum species, including C. verum/C. zeylanicum, C. cassia, C. loureiroi, and C. burmannii, each with distinct volatile profiles [42,101,102,103,104]. Chemical identity is further determined by the organ used for extraction. Bark, leaf, root, fruit, and flower oils from the same species may differ markedly in their dominant constituents. Across commercial and cultivated Cinnamomum verum leaf samples, major constituents include eugenol, benzyl benzoate, (E)-cinnamyl acetate, and (E)-cinnamaldehyde, indicating multiple benzenoid/phenylpropanoid chemotypes despite limited chloroplast divergence [10]. Bark oils are frequently rich in (E)-cinnamaldehyde, whereas leaf oils may contain greater proportions of eugenol, benzyl benzoate, cinnamyl acetate, linalool, camphor, or mixed phenylpropanoid–terpenoid profiles [9,42,105]. More broadly, leaf oils of C. cassia, C. loureiroi, C. burmannii, and related taxa are often cinnamaldehyde-rich, whereas C. verum leaf oils are often, though not uniformly, relatively enriched in eugenol and other benzenoid/phenylpropanoid constituents [10,42,101,102,103,104].

Comparative work shows that organ choice and species identity jointly structure chemotype, with markedly different dominant molecules reported across leaves, stem bark, and root bark [9]. These shifts are mechanistically consequential because they reconfigure the balance among electrophilic, phenolic, and terpenoid compounds, thereby altering the antimicrobial spectrum, antioxidant behavior, sensory profile, and likely tolerability [9,14,105,106]. Substantial diversification also occurs within individual species. Without direct connection and evidence in poultry, C. osmophloeum leaf oils have been classified into cinnamaldehyde-, cinnamyl acetate-, linalool-, camphor-, and mixed chemotypes, with corresponding differences in antifungal and antioxidant activity [33,107]. Surveys of C. bodinieri, C. camphora, and C. burmanni likewise reveal extensive chemotype radiation linked to geography and environment, with only partial phylogenetic constraint [108,109,110]. In C. verum bark, chemotype structure may also appear as quantitative mosaics rather than sharply discrete classes, with (E)-cinnamaldehyde remaining dominant but strongly patterned relationships evident among cinnamyl acetate, eugenol, benzyl benzoate, linalool, and β-caryophyllene [105]. Developmental stage adds another layer, as leaf ontogeny and oil-cell density influence both yield and constituent balance [101,111].

This distinction is evident in poultry research. Preliminary findings show that dietary cinnamaldehyde has been associated with improvements in body weight and feed efficiency, and with changes in intestinal microbial composition, including increased relative abundances of Faecalibacterium and Lactobacillus in some experiments [52]. Recent phytochemical characterisation of commercial cinnamon bark oil also indicates that activity is not explained by cinnamaldehyde concentration alone [112]. Minor constituents may alter membrane partitioning, volatility, sensory properties, chemical stability, and interactions among antimicrobial and redox pathways. Reporting the nominal percentage of cinnamaldehyde is therefore useful but insufficient for complete chemical characterisation. Collectively, these data indicate that cinnamon essential oils constitute a family of chemically distinct interventions rather than a single class of ingredients. For poultry studies, the preparation should be described according to species, plant organ, full major-constituent profile, cinnamaldehyde concentration, carrier, and formulation. A broiler trial using purified cinnamaldehyde, a cinnamaldehyde-rich bark oil, and eugenol-rich leaf oil, or a multi-oil blend does not test the same chemical exposure, even when each intervention is discussed under the broader category of cinnamon-derived phytogenics [32,34,113].

3.3. Clove (ClEO): Eugenol Dominance Without Chemical Uniformity

ClEO is chemically more concentrated around one major constituent than most rosemary or cinnamon oils. Eugenol is typically the largest fraction, accompanied by eugenyl acetate, β-caryophyllene, α-humulene, and smaller amounts of other volatile compounds [2,11,12]. This recurring composition supports describing ClEO as an eugenol-dominant phenylpropanoid oil. It does not, however, imply that all clove oils are chemically identical. Quantitative variation in eugenyl acetate and sesquiterpenes may alter volatility, pungency, oxidative stability, antimicrobial potency, and sensory acceptability [11,12,114,115]. Extraction and processing account for a significant portion of this variation. Hydrodistillation, steam distillation, microwave-assisted extraction, ultrasound-assisted extraction, and supercritical CO₂ recovery differ in selectivity and thermal exposure, and may shift the balance among eugenol, eugenyl acetate, and less-volatile sesquiterpenes [11]. Hydrolysis during extraction or storage may further alter the relationship between eugenol and its esterified forms. Consequently, an oil described as eugenol-rich still requires direct compositional analysis.

Mechanistically, eugenol combines a lipophilic aromatic structure with a phenolic hydroxyl group. This enables it to partition into microbial membranes while also donating hydrogen to radical species [115,116]. Its antimicrobial effects include altered membrane fluidity, leakage of cellular contents, disruption of ion homeostasis, interference with energy metabolism, and inhibition of biofilm-associated behavior [117,118,119]. Its phenolic structure also provides a plausible basis for antioxidant and anti-inflammatory activity [120,121,122]. Nevertheless, the activity of ClEO cannot be attributed solely to eugenol, as eugenyl acetate, β-caryophyllene, and other constituents may modify potency, spectrum, volatility, and cellular interactions [2,11,115]. This broader evidence is supported by eugenol-rich oils from other taxa, such as Ocimum gratissimum, in which very different mono- and sesquiterpene backgrounds generate distinct pharmacological signatures despite a shared dominant phenylpropanoid [123]. Within Syzygium aromaticum itself, intraspecific variation in eugenyl acetate and sesquiterpene balance remains less systematically resolved than in cinnamon or rosemary, suggesting that clove compositional diversity remains under-characterised rather than absent [11].

3.4. Comparative Summary and Implications

Comparatively, REO is the most chemically plastic but also the most clearly structured around monoterpene-rich profiles, making its effects highly dependent on chemotype and extraction history. Formulation is especially important for ClEO because eugenol-rich oils are volatile, intensely flavored, and poorly dispersible in aqueous systems [12,124,125]. Emulsification and encapsulation may improve dispersion, limit rapid volatilisation, reduce immediate sensory exposure, and alter release within the gastrointestinal tract or at the surface of poultry products [12,31,114]. Although evidence in broilers is limited, an emulsified CEO preparation at 300 mg/kg produced greater changes in body weight gain, feed conversion, antioxidant status, and intestinal microbiota than a non-emulsified treatment at the same nominal concentration; however, more research is needed to confirm this pattern [126]. Across meat and food systems, clove EO also improves oxidative stability, color retention, and shelf life [12,125]. However, these benefits should still be interpreted through a chemistry-aware framework, because the efficacy of a eugenol-dominant oil is not determined by eugenol alone, but by the compositionally defined system in which eugenol is embedded [2,11,12,106,114,115,116]. Taken together, these oils support a comparative conclusion: rosemary, cinnamon, and clove should be discussed as distinct, chemistry-defined interventions, with rosemary best suited to chemotype-based comparison, cinnamon to species- and organ-specific comparison, and clove to formulation- and minor-constituent-sensitive comparison. The next section shifts from composition to mechanism, showing how rosemary, cinnamon, and clove oils differ in their direct antimicrobial effects as concentration and route of exposure change.

4. From Direct Microbial Injury to Ecological Modulation: Concentration and Exposure Define the Mechanism

EOs can influence poultry-associated microorganisms through several mechanisms, but these mechanisms do not operate with equal importance at every concentration or in every biological compartment. At inhibitory and bactericidal concentrations, disruption of the bacterial envelope and loss of energetic homeostasis usually dominate [127,128]. At lower, growth-permissive concentrations, selected constituents may interfere with adhesion, motility, secretion systems, quorum sensing, or biofilm development [81,129,130]. During dietary exposure, the response becomes more complex because the intestinal environment modifies the concentration and persistence of active compounds [131]. At the same time, the host simultaneously alters mucus production, epithelial permeability, inflammation, nutrient flow, and the microbial habitat [60,132]. These compositional differences matter because they shape how each oil behaves mechanistically. Rosemary oils, which are typically dominated by monoterpenes, tend to act primarily through membrane partitioning, altered permeability, and ionic imbalance [81,127]. Cinnamon oils, especially cinnamaldehyde-rich preparations, add an electrophilic aldehyde function that can intensify envelope disruption and interfere with proteins and energy metabolism [128]. Clove oils, by contrast, are centered on eugenol, whose phenolic hydroxyl group supports both membrane-active and redox-related effects [129,130]. As a result, the same botanical label can imply very different antimicrobial, antioxidant, and sensory profiles, depending on the species, plant organ, and formulation. The next section therefore examines how these chemical differences translate into direct antimicrobial effects and, at lower exposure levels, broader ecological modulation in poultry systems. Figure 2 summarises the main composition-dependent mechanisms through which rosemary, cinnamon, and clove essential oils may influence poultry-associated microorganisms and host-relevant biological processes.

The direct antimicrobial activity of REO is primarily attributed to lipophilic monoterpenes, including 1,8-cineole, α-pinene, and borneol [133]. These compounds partition into the lipid phase of the cytoplasmic membrane (Figure 3) and may also disturb the outer membrane of Gram-negative bacteria [134,135]. Increased membrane disorder is followed by leakage of intracellular material, altered ion transport, impairment of respiratory processes, and loss of cellular energy [136,137]. In contrast, alginate coatings containing rosemary oil inhibited Listeria monocytogenes and the refrigerated spoilage microbiota [138,139]. These experiments demonstrate antimicrobial activity under direct-contact conditions, where the oil is retained near the bacterial surface. They do not establish that equivalent concentrations are achieved in the avian gastrointestinal tract. In vitro studies further report membrane damage, intracellular leakage, ATP depletion, and dose-dependent lysis in rosemary-treated bacterial systems [133]. In the cited in vitro studies, inhibitory or bactericidal activity against Salmonella and Escherichia coli occurred within the low-mg/mL range, and reductions on poultry-associated surfaces are often measurable but incomplete [133,138,139].

The antibacterial activity of cinnamaldehyde-rich CinEO is characterised by rapid disturbance of the bacterial envelope. In E. coli, exposure to cinnamaldehyde (CA) results in increased conductivity, leakage of cellular material, membrane wrinkling, separation of the inner membrane from the cell wall, and structural rupture at inhibitory concentrations [14,140,141]. In poultry-derived avian pathogenic E. coli isolates, reported CinEO MICs range from approximately 0.2 to 0.8 µL/mL, while CA prolongs the lag phase, increases membrane permeability, and reduces adhesion [14,142]. CA differs from rosemary monoterpenes in that its α,β-unsaturated aldehyde group also enables electrophilic interactions with cellular proteins. Membrane damage may therefore be accompanied by interference with transport proteins, respiratory enzymes, glucose utilisation, and ATP-generating pathways [14,134,143]. In Salmonella Enteritidis, cinnamon oil increased reactive oxygen species, lipid peroxidation, and protein oxidation and altered the abundance of outer membrane proteins such as OmpF, OmpA, and OmpX [14,141]. These multi-target effects disrupt nutrient transport, respiratory function, and ATP-dependent processes, thereby driving metabolic collapse rather than simple membrane leakage [14,134,141]. Cinnamaldehyde-rich treatments have also affected anaerobic respiratory pathways, type III secretion-associated processes, and cellular energy metabolism [134,143,144]. Susceptibility nevertheless varies among organisms. In a cooked-chicken model, inhibition of Clostridium perfringens required greater exposure than that reported for avian E. coli. However, differences in assay conditions and food matrices prevent a direct comparison of potency [142,145]. Differences in envelope structure, stress tolerance, growth conditions, and matrix composition therefore shape the observed response (Figure 4).

The contrast between in vitro and in vivo findings shows that dietary trans-cinnamaldehyde failed to reduce cecal Campylobacter jejuni in broilers despite marked activity against the same organism under laboratory conditions [146]. This does not contradict the membrane mechanism. It indicates that the active concentration achieved in the cecum, the duration of contact, digesta binding, microbial competition, and local physiology differed from those in the controlled in vitro system. Cinnamon oil is therefore a potent direct antimicrobial under sufficient contact exposure, but its in vivo performance cannot be predicted from MIC values alone. Chemical profile, protection during feed processing, release site, and effective luminal concentration are likely to determine whether the membrane-active potential is expressed in the bird.

Clove essential oil (ClEO) is dominated by eugenol, a phenolic phenylpropanoid that combines membrane affinity with hydrogen-donating redox activity [115,147,148]. Eugenol enters the phospholipid bilayer, increases membrane disorder and permeability, and promotes leakage of K⁺, ATP, and other intracellular constituents [148]. Disruption of the membrane potential and ion gradients compromises the proton-motive force, ATP synthesis, energy-dependent transport, and respiratory activity [148]. In experimental systems, eugenol exposure causes leakage of periplasmic markers, depletion of intracellular reducing equivalents, and severe morphological damage, while SEM observations confirm major cell distortion in exposed bacteria [115,147] (Figure 5). Downstream of this initial membrane hit, ClEO drives broader metabolic collapse. The loss of membrane potential and proton-motive force impairs respiration and central energy metabolism, while ROS overproduction amplifies damage through lipid peroxidation, protein oxidation, and DNA damage [148]. Eugenol-rich systems can increase intracellular reactive oxygen species, promote lipid and protein oxidation, impair enzymes associated with energy metabolism, and weaken ATP-dependent stress responses [148,149]. The magnitude of the response depends on bacterial envelope architecture. Staphylococcus aureus is often more susceptible than E. coli, consistent with the protective role of the Gram-negative outer membrane [115]. Lower concentrations may restrict growth, whereas higher concentrations can produce bactericidal damage. This concentration dependence matters because effects observed near or above the MIC should not be described as selective virulence attenuation unless bacterial growth has been performed at subinhibitory concentrations, which ensures bacterial survival and allows for further biological investigation.

Broiler studies provide evidence that eugenol-containing interventions can reduce the burden of intestinal pathogens. Dietary eugenol decreased Salmonella Typhimurium invasion and associated intestinal injury, while clove-containing EO mixtures reduced pre-cecal E. coli and Clostridium counts [61,150]. These in vivo responses are consistent with direct antimicrobial pressure, but they do not demonstrate that membrane collapse occurred via the same sequence observed in simplified laboratory systems [61,151]. At the same time, the actual effect size remains context-dependent because pH, bile, feed matrix, pathogen load, and formulation determine how much of the eugenol-rich fraction reaches the target site in active form. Under direct-contact conditions, ClEO induces membrane destabilisation, followed by loss of proton-motive force and broader energetic and oxidative injury [151,152,153]. Expression of this sequence in the avian intestine depends on the concentration and persistence of the active eugenol-rich fraction [61,115,147,148,149,150].

Across the three oils, direct bacterial killing is therefore most securely demonstrated under in vitro or food-contact conditions. Rosemary monoterpenes produce broad membrane perturbation, cinnamaldehyde combines envelope injury with electrophilic and metabolic interference, and eugenol links membrane disruption to redox and energetic damage [81,127,128,152]. Translation to the avian intestine depends on whether the relevant concentration is maintained at the target site [131,154]. The mechanisms described above explain how rosemary, cinnamon, and clove essential oils can suppress microorganisms with sufficient exposure. Still, they do not address a second major issue in the poultry literature: whether in vivo improvements translate into postmortem meat preservation. Because the intestinal environment, formulation, and target site differ so profoundly from the conditions governing meat storage, antimicrobial activity in the bird cannot be automatically translated into shelf-life effects. The next section, therefore, examines chemical non-equivalence and the limits of inferring postmortem meat stability from in vivo antioxidant status.

5. Chemical Non-Equivalence and the Limits of Inferring Postmortem Meat Stability from In Vivo Antioxidant Status

At the first level, a botanical name does not define a uniform intervention. Cinnamon oil may originate from bark or leaf and can differ substantially in the relative abundance of cinnamaldehyde, eugenol, cinnamyl acetate, benzyl benzoate, and other constituents [9,10,14,105]. Rosemary oils vary according to genotype, geographical origin, season, plant organ, and extraction method, producing cineole-, camphor-, verbenone-, or α-pinene-dominated profiles [7,8,65,88,89,93,113]. Although clove oil is generally characterised by a high eugenol content, extraction conditions, eugenyl acetate concentration, sesquiterpene composition, and subsequent processing can still alter its biological properties [11,114,115,116]. Consequently, oils carrying the same botanical label may differ in antimicrobial activity, antioxidant behavior, volatility, stability, sensory intensity, and interactions with biological membranes [92]. The problem extends beyond chemical composition alone. Extraction procedures, storage conditions, feed manufacture, carrier materials, and formulation technologies can alter the chemical profile that ultimately reaches the bird [155]. A GC–MS profile obtained immediately after extraction does not necessarily reflect the composition remaining after storage, feed mixing, pelleting, or gastrointestinal passage [155,156].

Formulation further complicates interpretation. EOs are volatile, lipophilic compounds whose effective exposure depends not only on the amount added to the diet but also on the route of delivery. Encapsulation, nanoencapsulation, emulsification, and related technologies can modify stability, release characteristics, and interaction with the gastrointestinal environment [14,43,126,157]. For example, nano-protected rosemary oil produced stronger physiological and intestinal responses than the corresponding free oil [157]. In contrast, encapsulated blends containing cinnamon, thyme, and clove oils generated greater improvements in performance and antioxidant-related parameters than non-encapsulated formulations [26]. Many poultry studies evaluate serum or plasma markers such as superoxide dismutase, glutathione peroxidase, catalase, total antioxidant capacity, reduced glutathione, or malondialdehyde [158,159]. While these measurements provide valuable information on the physiological redox status of the live bird, they do not directly demonstrate meat preservation after slaughter. The assumption that improved systemic antioxidant status automatically improves meat stability is attractive but biologically incomplete.

Slaughter represents a major biochemical transition rather than a continuation of the physiological state measured in vivo. Once circulation ceases, oxygen distribution changes, pH declines, mitochondrial regulation is progressively lost, cellular membranes become destabilised, and heme-associated iron becomes increasingly available to participate in oxidative reactions [113,160,161]. Subsequent deterioration is influenced by storage temperature, packaging atmosphere, light exposure, microbial contamination, processing conditions, freeze–thaw cycles, cooking, and product handling. These postmortem processes operate within a fundamentally different biological environment from that represented by blood antioxidant measurements collected before slaughter [162,163]. As a result, an essential oil treatment may improve circulating antioxidant indices without producing measurable improvements in meat preservation [164,165]. Conversely, a treatment may exert relatively modest effects on systemic antioxidant markers yet still influence postmortem stability by altering muscle composition, endogenous antioxidant reserves, membrane integrity, or other factors relevant to deterioration [163]. We view evidence of antioxidant activity in vivo as mechanistic support rather than direct proof of postmortem protection.

The distinction becomes evident when examining the available evidence for rosemary, cinnamon, and clove. Rosemary provides some of the strongest indications that dietary supplementation can influence postmortem quality, but even here the response is not universal. Yesilbag et al. [166] evaluated rosemary leaves and rosemary oil and measured both physiological and meat-quality parameters, thereby linking dietary exposure more directly to postmortem outcomes than studies restricted to blood biomarkers. Similarly, Adil et al. [35] reported reductions in breast-meat lipid deterioration indices following dietary supplementation with rosemary oil, particularly with nanoencapsulated formulations. However, Gumus and Gelen [167] observed reductions in TBARS in drumstick meat, but not consistently in breast meat or across all quality parameters. These findings suggest that dietary rosemary can influence postmortem stability under specific conditions. Yet, the magnitude and expression of the response depend on formulation, muscle type, storage conditions, and the parameter measured. A similar pattern emerges for cinnamon. Dietary cinnamon-derived products frequently improve antioxidant status, intestinal morphology, microbial populations, or metabolic traits in live birds. However, these physiological responses do not automatically demonstrate enhanced preservation of stored meat. Evidence for postmortem effects is strongest when meat itself is evaluated during storage [163], which showed improvements in oxidative stability and water-loss characteristics in stored breast muscle and affected the meat-quality traits [156]. Nevertheless, these findings remain more limited than the extensive evidence demonstrating preservation when cinnamon oil is applied directly through coatings, films, or active packaging systems [168,169,170,171]. Direct application places active compounds at the site of deterioration, whereas dietary supplementation requires successful transfer through digestion, absorption, metabolism, and tissue distribution before any postmortem effect can be observed.

6. Carcass Composition and Yield: Dietary Route as the Primary Evidence Class

Carcass traits and postmortem meat-quality traits should not be interpreted within the same causal frame. Carcass yield is generated before slaughter through growth efficiency, nutrient partitioning, organ development, intestinal function, inflammatory tone, and metabolic status. By contrast, lipid oxidation, nitrogenous spoilage, microbial growth, pH drift, water loss, and sensory deterioration develop after slaughter within the muscle matrix, the coating layer, the packaging headspace, or the processed product [172,173]. This route separation prevents a common overinterpretation in the phytogenic-feed literature: an essential oil that improves live-bird physiology does not necessarily improve stored meat, and a coating that preserves meat surface quality is irrelevant to carcass accretion. Carcass-related evidence for REO, CinEO, and ClEO should therefore be judged by biological proximity to pre-slaughter outcomes, including dressing percentage, breast yield, thigh yield, abdominal fat, organ weights, feed efficiency, nutrient utilisation, and intestinal function.

Among rosemary essential oil studies in broilers, the most carcass-specific evidence comes from the nanoencapsulated REO trial of Adil et al. (Figure 6), because growth performance, nutrient digestibility, carcass traits, meat quality, and growth- and inflammation-related gene expression were measured within the same experimental design [35]. Dietary supplementation with 200 mg/kg nanoencapsulated REO increased pre-slaughter live weight, dressing percentage, breast yield, and thigh yield, while reducing abdominal fat relative to the unsupplemented control. Numerically, dressing percentage increased from 70.36% to 72.49%, breast yield from 18.03% to 21.49%, thigh yield from 8.98% to 10.49%, and abdominal fat decreased from 1.24% to 1.14% of live weight [35]. These carcass responses coincided with improved feed conversion, dry matter and crude protein digestibility, upregulation of MUC2, PepT1, and IL-10 transcripts, and downregulation of TNF-α transcript expression. The response, therefore, does not establish a direct anabolic effect of rosemary volatiles on muscle deposition. A more defensible interpretation is that nanoencapsulation likely increased the apparent biological efficacy of REO, thereby supporting nutrient utilisation, barrier function, and inflammatory control, with secondary effects on breast and thigh yields. However, the study design does not permit a direct comparison between free and nano-encapsulated forms at identical delivered concentrations [35].

Earlier evidence from broiler studies supports this formulation-sensitive interpretation. Yesilbag et al. reported that dietary rosemary volatile oil at 100–200 mg/kg affected live-weight gain, feed efficiency, and carcass yield more clearly than dried rosemary leaves, suggesting that the concentrated volatile fraction may exert stronger biological activity than the whole botanical matrix [166]. Mathlouthi et al. provide growth-efficiency evidence rather than direct carcass-partitioning evidence: REO at 100 mg/kg improved body weight, body-weight gain, and gain: feed to a level comparable with oregano EO, the rosemary–oregano combination, and avilamycin [174]. A related nano-protected REO study further supports the gut–metabolic mechanism by reporting improvements in lipid profile, immune-antioxidant status, cecal microbiota, villus height, and villus height-to-crypt depth ratio (VH:CD ratio), but it should not be used as primary evidence for carcass composition [157]. Similarly, Cetin et al. reported that 300 mg/kg rosemary EO improved final body weight, whereas combined oregano–rosemary EO improved body-weight gain, feed conversion ratio, and cecal microbial balance by reducing coliforms and clostridia and increasing lactobacilli [175].

For cinnamon-derived interventions, current evidence does not support a simple or universal carcass-yield-promoting effect of CinEO or CA in healthy broilers. In one of the clearest direct cinnamon-oil trials, Symeon et al. reported that dietary Cinnamomum zeylanicum oil at 0.5 or 1.0 mL/kg did not significantly affect body weight, feed intake, feed conversion ratio, internal organ weights, carcass yield, breast percentage, or leg percentage [165]. This null response indicates that cinnamon oil, under non-challenged conditions, does not necessarily redirect nutrient use toward carcass deposition. Gomathi et al. similarly observed no significant carcass response when cinnamon oil was combined with sodium butyrate, whereas Yang et al. showed that encapsulated CA mainly improved intestinal morphology, nutrient digestibility, transporter-related gene expression, gut microbial composition, and meat tenderness-related traits rather than establishing CA as a direct carcass-yield enhancer [156,176].

This interpretation is reinforced by Saied et al., whose cinnamon oil was chemically dominated by CA, which accounted for 77.16% of the oil, with eugenol accounting for 1.86% [177]. In that study, cinnamon-oil supplementation increased slaughter body weight, particularly at 500 mg/kg, but carcass percentage remained statistically unchanged, dressing percentage only approached significance, and gizzard percentage was the only carcass-related variable significantly affected. This pattern suggests that cinnamon oil may improve live growth or digestive activity without producing a proportional improvement in carcass yield. The gizzard response is also consistent with a digestive-function component rather than a direct anabolic effect on breast or carcass tissue [177].

Additional cinnamon-oil-based phytobiotic studies strengthen the proposed gut–metabolic pathway, although carcass outcomes were secondary or incompletely characterised in these experiments. Krauze et al. reported that a phytobiotic containing cinnamon oil administered in drinking water improved intestinal microbiology and histology while reducing MDA, lipid hydroperoxides, cholesterol, triacylglycerols, non-esterified fatty acids, and IL-6, indicating broad metabolic and redox modulation rather than a direct carcass-deposition mechanism [178]. In a larger follow-up trial, a cinnamon-oil/citric-acid phytobiotic improved final body weight and FCR, particularly at 0.25 mL/L, while also improving intestinal morphometry, microbiome balance, lipid metabolism, immune status, and antioxidant capacity. These findings strengthen the view that cinnamon-oil preparations may improve the biological efficiency of the living bird, but the response is expressed primarily through gut function, inflammatory tone, lipid metabolism, and oxidative stability rather than through consistent increases in dressing percentage or breast yield [32].

The strongest positive carcass evidence appears under pathological or inflammatory challenge rather than under normal physiological conditions. In broilers experimentally infected with Eimeria tenella, Qaid et al. showed that dietary cinnamon bark powder mitigated challenge-associated impairment in growth, carcass characteristics, and breast-meat quality relative to infected untreated birds [179]. Because Qaid et al. used cinnamon bark powder in an Eimeria tenella challenge, the study should be interpreted as evidence of cinnamon-derived stress resilience rather than direct evidence of CinEO carcass effects. What appears as carcass improvement may therefore be a secondary consequence of reduced intestinal damage, lower metabolic disruption, and preserved feed utilisation during challenge. This stress-resilience interpretation is further supported by Kang et al., who validated an encapsulated CinEO product under commercial broiler conditions and reported improved jejunal VH:CD ratio, reduced faecal oocyst counts, and lower necrotic-enteritis incidence and mortality during an outbreak, although final body weight did not differ significantly among treatments [180].

Clove-derived interventions require similar evidence-class separation. Dietary clove seed or powder, dietary clove oil, isolated eugenol, clove extract, ClEO nanoemulsions or coatings, ClEO-containing blends, and active packaging systems differ in chemistry, dose, route of exposure, tissue contact, and proximity to the postmortem deterioration site. Only the dietary categories are directly relevant to carcass composition and yield. The most direct carcass-focused broiler study is that of Suliman et al., because it measured carcass characteristics and body composition alongside meat-quality traits rather than inferring carcass value from live weight alone [181]. Dietary inclusion of clove seed (Syzygium aromaticum) powder at 1–6% in Ross 308 broilers did not significantly affect dressing percentage or absolute carcass component yields, despite a linear decrease in final body weight at higher inclusion levels [181]. Suliman et al. also reported increased relative weights of the gizzard and heart at low clove inclusion levels (1–2%), which may reflect digestive organ adaptation to clove bioactives rather than an improvement in marketable carcass composition [181].

Our interpretation is that across the three oils, the carcass evidence suggests a possible pattern. REO provides the clearest carcass-specific dietary signal when nanoencapsulated and linked to improved nutrient utilisation. CinEO/CA responses are more often expressed through gut–metabolic efficiency or challenge resilience than through consistent carcass repartitioning. ClEO/eugenol evidence remains conditional and depends strongly on diet context, botanical form, and whether the intervention is clove seed, clove oil, or isolated eugenol. The discussion therefore shifts from carcass accretion to meat deterioration, where dietary and postharvest interventions act at different stages of the production continuum. Carcass composition provides the clearest evidence for dietary effects before slaughter, but it does not capture what happens once the bird has been processed into meat. The next stage of the review, therefore, turns to lipid oxidation and spoilage chemistry, where the relevant question is not whether an essential oil improved live-bird performance, but whether it can slow deterioration in the meat matrix itself. This shift is important because the mechanisms driving carcass yield and postmortem shelf life are biologically distinct, even when they arise from the same dietary intervention.

7. Lipid Oxidation and Spoilage Chemistry: Dietary and Postharvest Routes Must Be Separated

Lipid oxidation and spoilage chemistry require a route-based interpretation. Dietary EO supplementation can influence the bird prior to slaughter by modulating antioxidant reserves, lipid metabolism, inflammatory burden, gut function, and the muscle’s intrinsic susceptibility to deterioration [34,35,60]. Postharvest systems act at a different biological level. Coatings, films, nanoemulsions, dipping treatments, modified-atmosphere packaging (MAP), active packaging, and incorporation into processed products deliver volatile or phenolic compounds directly to the meat surface, packaging headspace, or comminuted matrix [173,182]. This distinction matters because hydroperoxide formation, aldehyde accumulation, exudate-driven microbial growth, TVB-N development, pH drift, and sensory deterioration occur after slaughter, under storage conditions that are only partly shaped by the live bird (Figure 7).

For REO, the most convincing recent dietary evidence comes from Adil et al., who evaluated several indices of lipid deterioration in broiler breast meat rather than relying on TBARS alone [35]. In broilers fed free or nanoencapsulated REO, breast-meat TBARS, FFA, and PV were reduced, with the most consistent responses observed in the nanoencapsulated groups. At day 0 of storage, REO_N100 and REO_N200 reduced all three markers compared with the control, whereas at day 5, REO_F200, REO_N100, and REO_N200 maintained lower TBARS, FFA, and PV values [35]. Importantly, pH at 0 and 24 h after slaughter remained unchanged despite reductions in lipid-deterioration markers and improvements in water-related traits. Thus, the REO response should be interpreted as improved oxidative stability rather than as direct modulation of postmortem glycolysis [35]. Earlier dietary work by Yesilbag et al. remains useful as foundational evidence in broilers. That study compared dried rosemary leaves, rosemary volatile oil, and α-tocopherol acetate in broiler diets while measuring performance, meat pH, color, TBA/MDA values, sensory traits, and bacterial counts [166].

Rosemary volatile oil was supplied at 100, 150, and 200 mg/kg, and TBA analyses were performed on breast meat during refrigerated storage after slaughter. Meat from birds fed rosemary or rosemary volatile oil showed lower TBA/MDA values than meat from birds receiving α-tocopherol acetate alone, indicating that rosemary-derived dietary supplementation can improve postmortem oxidative stability in broiler breast meat [166]. However, the pH response should remain mechanistically separate from lipid oxidation. Differences in breast or thigh pH most likely reflect postmortem metabolic and microbial conditions rather than a direct antioxidant effect. The dietary REO evidence is supportive but not uniform. Gumus and Gelen reported that 100 or 200 mg/kg dietary REO did not significantly affect breast-meat TBARS, whereas drumstick TBARS were reduced on days 0, 2, and 4, and the pH of breast and drumstick meat was not significantly altered [167]. This muscle-specific response is biologically plausible because drumstick meat contains more heme pigments, mitochondrial residues, and lipid-associated pro-oxidant systems than breast meat. Rosemary powder evidence from Rostami et al. also supports an antioxidant direction, because rosemary powder combined with vitamin E reduced MDA accumulation in chilled broiler breast meat during storage [183]. Nevertheless, this should be labelled as rosemary powder evidence rather than direct REO evidence, because powder, extract, and essential oil differ in chemical composition, release kinetics, tissue exposure, and expected biological activity.

Li et al. extended this logic to non-contact preservation under MAP (modified-atmosphere packaging) [184]. They developed a solid spice essential-oil preservative containing rosemary and cinnamon EOs at a 1:1 ratio and combined it with MAP composed of 30% CO₂ and 70% N₂ to preserve chilled chicken breast [184]. Compared with MAP alone, the combined EO–MAP system reduced TVB-N, total viable count, and TBARS by 16.19%, 32.21%, and 21.28%, respectively, after 14 days of storage, and extended shelf life by approximately 13 days compared with air-packaged controls [184]. Because the preservative combined rosemary and cinnamon EOs, the study provides evidence for a mixed-oil headspace system rather than for REO in isolation [184]. Other postharvest REO systems define the same boundary. Fiore et al. developed PLA-based active films coated with chitosan or chitosan/caseinate enriched with 1–2% REO for fresh minced chicken breast, and the REO-containing films reduced MDA accumulation, supporting active packaging as a targeted strategy for controlling lipid oxidation at the meat surface [185]. Kahraman et al. provide a useful caution for free REO: in poultry fillets, 0.2% REO was the highest sensorially acceptable concentration; at this level, it did not reduce Salmonella Typhimurium or Listeria monocytogenes, but it reduced TBA/MDA accumulation when combined with MAP [186]. Because pH was unchanged, the study supports REO + MAP as a lipid-oxidation control strategy rather than a broad antimicrobial or pH-modifying intervention. Santi et al. also showed that chicken breast treated with 1% REO plus scCO₂MAP had extended microbial shelf life without significant changes in pH or water activity, suggesting that REO-based preservation can improve microbial stability without destabilizing basic physicochemical traits [187].

Processed poultry products provide matrix-specific REO evidence. Ghasemi et al. evaluated chicken nuggets formulated with 600 ppm rosemary, marjoram, clove, or sage EO and stored at −18 °C for three months [188]. The strength of this study is its simultaneous measurement of PV and TBARS/MDA, separating primary hydroperoxide formation from secondary aldehyde accumulation. Rosemary oil-treated nuggets showed the lowest MDA concentration and peroxide value after frozen storage, reaching 1.05 mg MDA/kg and 2.82 meq/kg, respectively [188]. The incorporation of EOs did not significantly alter nugget proximate composition, and rosemary-treated samples remained sensorially acceptable, supporting REO as a natural antioxidant in processed poultry matrices. Abbasi et al. used REO as a partial or total nitrite substitute in chicken sausages and reported that 120 ppm REO decreased lipid oxidation and increased sausage pH, while partial replacement of nitrite with REO helped preserve product quality [189]. In chicken meatballs, rosemary preparations also reduced lipid oxidation, although ethanol extracts performed better than REO, suggesting that phenolic-rich rosemary extracts may outperform volatile oils in some cooked or comminuted poultry systems [190]. A similar extract-based antioxidant pattern has been reported in poultry pâté [191]. Rosemary extracts are generally richer in phenolic diterpenes, whereas REO is dominated by volatile monoterpenes. Consequently, findings from rosemary extract have limited transferability to REO, and vice versa. Rosemary preparations differ in their dominant chemistry. Extracts are typically enriched in phenolic diterpenes such as carnosic acid and carnosol, whereas REO is dominated by volatile monoterpenes, including 1,8-cineole, α-pinene, and camphor. Their antioxidant activity consequently depends on different patterns of retention, dispersion, release, and interaction with the poultry matrix [190,192,193].

Jimoh et al. provide more direct dietary-to-meat evidence because they evaluated oxidative behavior in stored Pectoralis major, not only in serum or liver markers [163]. In that study, oral supplementation with Cinnamomum zeylanicum EO was associated with reduced lipid peroxidation and improved antioxidant-enzyme behavior during storage, supporting the possibility that pre-slaughter CinEO exposure may improve postmortem oxidative stability when the meat itself is assessed during storage [163]. Other dietary studies better support a gut–redox mechanism than direct meat preservation. Encapsulated CA at 100 mg/kg produced only a tendency toward higher 24 h meat pH, with all pH values remaining within the normal range; clearer responses were associated with intestinal morphology, nutrient digestibility, microbiota, and reduced Warner–Bratzler shear force rather than major shifts in postmortem acidification [156]. Similarly, graded CinEO supplementation affected immune response, liver MDA, intestinal morphology, and cecal microbial ecology, while 400 mg/kg CinEO improved oxidative-stress-related indices, immune response, and intestinal morphology without adverse histological effects [194].

Postharvest ClEO and clove-extract systems show a more consistent oxidative-stability signal. In chicken fillets, ClEO-loaded nanoemulsion coatings reduced PV and TBA/TBARS-type oxidation indices, lowered TVB-N, and inhibited total viable and psychrophilic bacterial growth [173]. In that study, the oil was eugenol-dominant, with eugenol at 88.38% and β-caryophyllene at 6.01%, and the 1% ClEO nanoemulsion was selected as the optimal treatment within that experimental design. In chicken meatballs, nanoencapsulated clove oil reduced TBARS and retarded redness loss while suppressing microbial counts [182]. In broiler fillets challenged with decontamination treatments, clove oil performed worse than peroxyacetic acid for immediate bacterial suppression but improved oxidative stability and appearance relative to harsher oxidising sanitisers [195,196]. Together, these studies suggest that the available evidence supports the antioxidant activity of clove-derived preparations at the meat surface.

Processed poultry systems provide additional matrix-specific evidence. In fresh chicken sausages, 0.25% clove oil produced lower TBARS, higher total phenolic content, higher DPPH activity, and lower microbial counts than the control, extending shelf life by approximately 4–5 days [197]. In vacuum-packaged chicken sausages stored at −18 ± 2 °C for 45 days, EO-treated products had lower pH and TBARS than controls, and clove-oil-containing treatments showed one of the slowest increases in lipid oxidation [198]. In EO blends, the B-2 combination containing clove oil, holy basil oil, and thyme oil produced the best oxidative-stability response among the tested blends [198,199,200]. In alginate coatings, clove EO combined with lemon verbena EO and MAP produced the lowest TBA value after 15 days; the clove oil in this system was eugenol-rich, with eugenol representing 79.4% of identified compounds, followed by β-caryophyllene and eugenol acetate [199]. In chicken nuggets stored at −18 °C for three months, 600 ppm ClEO reduced peroxide development and TBARS accumulation; by day 90, clove-treated nuggets had one of the lowest TBARS values, close to rosemary-treated nuggets [188].

Overall, the evidence for lipid oxidation and spoilage indicates that REO, CinEO, and ClEO occupy distinct evidence profiles rather than a single antioxidant hierarchy [167,173,182,201]. REO has support across dietary and postharvest routes, CinEO is particularly well-represented in structured delivery systems, and ClEO/eugenol has the clearest phenolic chain-breaking rationale [173,201,202,203]. CinEO appears especially consistent in coatings, films, nanoemulsions, and active packaging, whereas dietary evidence mainly supports upstream gut–redox modulation unless the meat is assessed directly over storage [168]. ClEO/eugenol has the clearest phenolic antioxidant rationale and strong evidence for postharvest preservation, but dietary carryover into poultry muscle remains unproven [173,182,202]. Across all three oils, the most defensible conclusion is route-specific: dietary supplementation may lower intrinsic susceptibility before slaughter, whereas postharvest delivery systems more directly control oxidation, spoilage chemistry, and sensory deterioration at the site where meat deterioration begins [167,173,201,203]. The route-based distinction between dietary supplementation and postharvest application also helps explain why meat-quality traits such as water-holding capacity and tenderness do not always correlate simply with lipid oxidation [204]. Even when an essential oil reduces peroxide or TBARS values, the effects on texture depend on how effectively the treatment preserves muscle structure, protein functionality, and water retention during storage [182,204,205]. The next section, therefore, focuses on water-holding capacity, drip loss, texture, and tenderness as secondary outcomes of oxidative and structural preservation.

8. Water-Holding Capacity, Drip Loss, Texture, and Tenderness: Secondary Effects of Oxidative and Structural Preservation

Water-holding capacity, drip loss, cooking loss, shear force, and tenderness are structural attributes of meat quality rather than direct measures of antioxidant protection (Figure 8). They reflect the combined consequences of postmortem pH decline, myofibrillar protein denaturation, membrane integrity, proteolysis, sarcomere structure, fiber type, cooking-induced shrinkage, and the analytical method used to quantify water retention [204,206,207]. This distinction matters because an essential oil may reduce TBARS or peroxide values without improving tenderness, and reduced drip loss does not necessarily indicate direct modification of myofibrillar proteolysis [206,207].

Within this framework, the REO evidence for WHC and texture is narrower than its evidence for lipid-oxidation control. The clearest dietary support comes from Adil et al., where nanoencapsulated REO improved WHC and reduced drip loss without altering pH at 0 or 24 h after slaughter [35]. This pattern points away from altered postmortem acidification and toward secondary preservation of membrane or myofibrillar integrity. In the same study, WHC increased from 54.17% in the control to 56.41% in REO_N200, drip loss decreased from 3.11% to 2.85%, and extract release volume increased from 25.17% to 29.37% [35]. These changes are useful, but they should be described as modest, formulation-dependent improvements in water-related quality rather than as evidence that REO directly improves tenderness. The broader rosemary literature supports this cautious interpretation. Gumus and Gelen supplemented broiler diets with 100 or 200 mg/kg REO but measured water activity rather than classical WHC, drip loss, cooking loss, or shear force; their findings therefore support discussion of microbial and oxidative stability, but not direct claims about improved water retention or tenderness [167]. Studies of rosemary extract and powder broaden the evidence base for rosemary, whereas REO-specific conclusions depend on experiments with the volatile oil itself. Liu et al. reported that dietary rosemary extract reduced cooking loss in broiler breast muscle, whereas WHC and shear force did not change significantly [208]. Wang et al. measured cooking loss, shear force, and drip loss in broilers fed rosemary powder, but most indices of water retention and tenderness remained unchanged [209]. Together, these findings indicate that rosemary-derived preparations may protect selected physical meat-quality traits under certain conditions, but the response depends on the chemical form, delivery route, and the specific trait examined.

Processed poultry products provide a separate matrix-dependent line of evidence. In chicken burgers, chitosan coatings containing free or nanoliposomal REO affected hardness and slowed physicochemical and sensory deterioration during refrigerated storage, with the strongest preservation effect reported for the 2% chitosan + REO nanoliposome treatment [210]. Sutha et al. evaluated the effect of REO in chicken nuggets and found no significant effects on pH, emulsion stability, product yield, or shear force, although 0.10% REO improved flavor and overall acceptability [211]. Importantly, because comminution, formulation, coating structure, fat distribution, and cooking alter water mobility and texture, findings from processed poultry products have limited transferability to intact fresh broiler breast muscle. Overall, REO should be described as a formulation-sensitive antioxidant with potential secondary effects on water retention, rather than as a proven tenderising agent.

The physical meat-quality response to cinnamon-derived additives likewise varies by trait assessed. Gomathi et al. found no significant effect of dietary cinnamon oil combined with sodium butyrate on pH, WHC, shear force, or cooking loss [176]. Huang et al. likewise showed that CA alone did not reduce drip loss in broiler breast meat, with clearer improvements associated with vitamin C or the combined cinnamaldehyde–vitamin C strategy [212]. By contrast, Yang et al. reported that encapsulated CA reduced Warner–Bratzler shear force, particularly at 100 mg/kg, where WBSF decreased from 1.95 kg in the negative control to 1.33 kg [156]. This supports a possible tenderness-related response but cooking loss and drip loss were not significantly improved in the same study. The interpretation should therefore be specific: encapsulated CA may influence shear force under certain dietary conditions, but it does not consistently improve all determinants of water loss.

Jimoh et al. provide dietary-to-meat evidence from a comparative spice-essential-oil experiment that included Cinnamomum zeylanicum [163]. In that study, broilers orally supplemented with CinEO produced breast meat with lower cooking loss and the lowest drip loss among treatments; control meat had cooking loss of 34.17% and drip loss of 4.50%, whereas the CinEO group had cooking loss of 24.17% and drip loss of 1.50% [163]. This links pre-slaughter CinEO exposure with measurable changes in postmortem water loss. Even here, however, the conclusion should remain restrained: the result supports storage-context preservation of water-related quality, not a universal effect of CinEO on intrinsic WHC in fresh broiler muscle. A plausible mechanism is that reduced lipid peroxidation and improved antioxidant-enzyme activities helped preserve membrane and myofibrillar integrity during storage, thereby limiting exudate formation and cooking loss [163]. Older non-broiler evidence from Japanese quail provides useful context but remains secondary because species and production conditions differ [213]. CA-containing phytogenic blends add mechanistic but not compound-specific support. İpçak and Alçiçek tested CA, carvacrol, capsicum oleoresin, and their mixture in broiler diets and directly measured thawing loss, cooking loss, WHC, toughness, and firmness [214]. CA improved thawing loss in leg meat, whereas the combined phytogenic treatment improved cooking loss and sensory traits such as tenderness and juiciness, indicating a formulation- and muscle-dependent response. Mullenix et al. evaluated a microencapsulated phyto/phycogenic blend containing thymol, CA, and eugenol and measured breast fillet pH, drip loss, colour, and sensory texture, but found no significant differences in drip loss or sensory texture [215].

For clove-derived interventions, the physical meat-quality evidence is more limited and more dose-sensitive than the oxidation evidence. Suliman et al. reported improved WHC and lower shear force in broilers fed 1–2% clove seed powder compared with controls [181]. This suggests a possible improvement in water retention and tenderness-related traits at low inclusion levels. Because the intervention used whole clove seed powder, the findings are specific to that botanical matrix and dose range and do not isolate an effect of ClEO. Dietary eugenol altered pH and color but did not improve drip loss, cooking loss, or WHC [216]. In chicken meatballs preserved with nanoencapsulated ClEO, microbial and oxidative stability improved while WHC and texture were essentially maintained rather than transformed [182].

Protein oxidation is a major unresolved link between lipid oxidation and texture in the literature. Even when lipid oxidation is controlled, myofibrillar protein oxidation can reduce solubility, alter gelation, impair water binding, and modify tenderness. Poultry-specific storage studies show that breast and thigh proteins undergo oxidation-related changes during storage [217]. Yet most poultry/clove studies still rely on TBA/TBARS, PV, pH, TVB-N, and microbial counts, with little integration of protein carbonyls, sulfhydryl depletion, myofibrillar fragmentation, proteolytic status, or microstructural imaging [173,182,218]. This gap matters because it remains unclear whether clove preserves texture by stabilising proteins, limiting membrane oxidation, slowing microbial spoilage, modifying postmortem metabolism, or simply delaying sensory rejection through aroma and flavour effects. Current clove studies document selected tenderness-related responses, but the contributions of protein oxidation, proteolysis, membrane preservation, and muscle microstructure remain unresolved [217].

Across REO, CinEO, and ClEO, the physical meat-quality evidence is less consistent than the lipid-oxidation evidence. REO has the clearest dietary signal when nanoencapsulated, but the magnitude of WHC and drip-loss improvement remains modest and formulation-dependent. CinEO/CA shows selected improvements in cooking loss, drip loss, or shear force, particularly when delivered through coatings, films, microcapsules, or mixed phytogenic systems. Still, responses are not uniform across dietary trials. ClEO/eugenol shows conditional effects on water retention and texture, with stronger support for maintaining quality during storage than for directly improving intrinsic tenderness. Therefore, water-loss and texture outcomes should be discussed as secondary, matrix-sensitive consequences of structural preservation rather than as primary EO targets.

9. Conclusions

In conclusion, purified or synthetically produced compounds corresponding to major essential-oil constituents represent valuable complementary feed-additive options because they provide defined composition, improved standardisation, and clearer alignment with quality-control and regulatory expectations. However, this review emphasises that natural essential oils should not be interpreted simply as carriers of a single dominant molecule. Their biological behavior in poultry systems is shaped by the combined influence of major and minor constituents, chemotype, botanical source, extraction history, storage, formulation, dose, and route of exposure. Therefore, rosemary, cinnamon, and clove essential oils should be evaluated as chemically complex, composition-dependent interventions rather than interchangeable phytogenic additives. Rosemary, cinnamon, and clove essential oils should be regarded as chemically distinct, formulation-sensitive interventions rather than interchangeable phytogenic additives. Their biological effects in poultry depend on botanical source, chemotype, extraction method, storage history, dose, formulation, and route of exposure. Across the poultry literature, the strongest and most consistent evidence for these oils concerns gut function, microbial modulation, oxidative balance, and postharvest preservation, though even here the effects are context-dependent. Dietary supplementation may improve intestinal morphology, inflammatory status, nutrient utilisation, and, in some cases, carcass traits or meat storage stability. Postharvest applications are generally more reproducible because the active compounds are delivered directly to the meat surface, packaging system, or product matrix where deterioration occurs. Overall, the literature supports route- and chemistry-specific interpretation of essential oil effects in poultry. Dietary use should be evaluated primarily for live-bird performance, gut health, and pre-slaughter physiological effects. In contrast, postharvest use should be assessed using direct meat-quality and shelf-life endpoints. This review also highlights major limitations in the current evidence base. Although rosemary, cinnamon, and clove essential oils are widely discussed as promising poultry interventions, studies are difficult to compare because they often use chemically non-equivalent preparations that differ in botanical source, chemotype, extraction method, storage, formulation, dose, and route of exposure. Apparent inconsistencies may therefore reflect differences between interventions rather than true biological disagreement. Evidence is further limited by heterogeneous experimental designs, variable dose reporting, unequal study quality, and frequent failure to distinguish free oils from protected formulations or dietary supplementation from postharvest use. Many studies also assess isolated endpoints rather than integrating chemical composition, biological compartment, and storage conditions, which limits mechanistic interpretation. In vivo antioxidant changes should not be overinterpreted as proof of postmortem meat protection, since these are biologically distinct processes. Future studies should standardise GC–MS profiling, report chemotype, plant organ, extraction, storage, formulation, and dose, compare free and protected formulations directly, and include paired measurements of antioxidant status, protein oxidation, microstructure, storage, dose–response, and release kinetics.