Black Cumin (Nigella sativa) as a Healthy Feed Additive for Broiler Production: A Focused Review

Abstract

Following restrictions on antibiotic growth promoters in poultry production, there is growing interest in natural feed additives that support health and productivity. Among these, black cumin (Nigella sativa) has emerged as a promising candidate due to its antioxidant, antimicrobial, and immunomodulatory properties. Most studies report that black cumin, in the form of whole seeds, seed meal, or seed oil, improves body weight gain and feed conversion ratio, enhances antioxidant and immune status, and provides additional benefits on lipid profiles, liver enzymes, and cecal microbial balance. This review provides a focused synthesis of recent studies (2014–2025) on black cumin supplementation in broiler chickens, considering its various forms (whole seeds, seed meal, seed oil, and nano-formulations) and production contexts (healthy, heat-stressed, and disease-challenged birds). Specifically, this review compares responses across different forms and doses, evaluates effects on growth performance, immune function, gut health, antioxidant status, liver metabolism, and meat and carcass quality, and highlights inconsistencies among studies. Additionally, it identifies key research gaps to guide future investigations, including optimal dosing, long-term safety, and practical applications in commercial production. Overall, black cumin shows potential as a natural alternative to antibiotics, but further standardized, large-scale studies are needed to confirm its efficacy and feasibility in sustainable poultry farming.

1. Introduction

Poultry farming is a rapidly growing industry that provides high-quality protein at an economical cost [1]. Broiler performance has improved substantially through genetic modifications and optimized diet formulations [1]. In poultry nutrition, feed additives such as antibiotics, prebiotics, and probiotics are commonly used as growth promoters to enhance nutrient utilization and feed efficiency, with antibiotics traditionally being the most widely employed growth promoter [2].

For over 50 years, antibiotics have been used in livestock in the United States and other countries [3]. Historically, most were administered not to treat disease but for growth promotion and disease prevention, typically at subtherapeutic levels of dose [4]. Due to the link between antimicrobial resistance and antibiotic use, many countries now restrict antibiotics to treating sick animals [4]. The European Union banned nontherapeutic antibiotic use in animals in 2006, and the U.S. FDA introduced a voluntary reduction policy in 2012 to lower resistant organisms in the environment [4]. Therefore, ensuring the proper use of antimicrobials in veterinary medicine remains a key strategy in mitigating resistance [5]. Over the past two decades, nutritionists and pharmacists have developed replacements to maintain or enhance animal health and productivity [6]. In response to the growing concerns about antibiotic resistance, researchers have increasingly focused on natural growth promoters, including medicinal plants such as Nigella sativa [7], and phytogenic feed additives have emerged as promising alternatives to antibiotic growth promoters [8].

Nigella sativa, commonly known as black cumin, is an herbaceous plant (20–60 cm in height) widely recognized for its distinctive aroma and culinary uses, especially in the Mediterranean region, where it is predominantly cultivated. Beyond its culinary applications, black cumin seeds have long been valued for their medicinal properties across various cultures. Nigella sativa seeds contain a variety of bioactive compounds, particularly in the essential oil, including thymoquinone (27.8–57.0%), p-cymene (7.1–15.5%), carvacrol (5.8–11.6%), t-anethole (0.25–2.3%), 4-terpineol (2.0–6.6%), and longifolene (1.0–8.0%) [9]. Black cumin exhibits a broad spectrum of pharmacological activities, including analgesic, anti-inflammatory, antimicrobial, antidiabetic, anticancer, immune-modulatory, hepatoprotective, and renal-protective effects [7,10]. Additionally, black cumin seed oil is rich in unsaturated fatty acids, which may contribute to improving breast meat fatty acid profile and potential human health benefits [11].

Black cumin has shown promising effects on growth performance, immune function, gut health, inflammation, and meat quality in broiler chickens [12]. Specifically, it increases protein content [13], enhances sensory attributes such as tenderness and flavor [14], improves the unsaturated fatty acid profile [11], and reduces lipid oxidation in breast muscle [14]. Given broilers’ focus on rapid growth and high meat yield, they are particularly well-suited for dietary interventions that promote both health and productivity.

This review focuses exclusively on broiler chickens, the fastest-growing segment of the poultry industry, with distinct nutritional and management needs compared to other poultry, such as layers. While several reviews have summarized phytogenic additives in poultry, few have focused on black cumin across its various forms (seed, oil, and nano-formulations) and under different production contexts (healthy, heat-stressed, and disease-challenged broilers). This review aims to provide a more integrated synthesis by (i) comparing responses across forms and doses, (ii) highlighting differences between normal and stress conditions, and (iii) outlining key research gaps to guide future studies.

To evaluate the potential of black cumin supplementation in broiler diets, this review synthesizes findings from recent studies published between 2014 and 2025. A comprehensive literature search was conducted using PubMed and Google Scholar, employing search strategies that included terms such as “Nigella sativa”, “black cumin”, “broiler”, “broiler chicken”, and “feed additive”. Only English-language original research articles were included, and reviews, conference abstracts, and non-peer-reviewed materials were excluded. While this review is not a fully systematic review in design, it applies consistent inclusion criteria to provide a focused and evidence-based synthesis. To facilitate analysis, studies are grouped according to key performance traits and physiological domains rather than a formal meta-analysis. Due to heterogeneity in study designs and limited standardized trials, this review employs a thematic narrative approach—grouping studies by key traits—rather than a formal systematic review or meta-analysis.

This review focuses on black cumin in various forms—whole seeds (ground or crushed), seed meal, seed oil, or essential oil—in healthy broiler chickens raised under standard or heat stress conditions, as well as in disease-challenged models. Studies involving mixed herbal formulations were excluded to avoid confounding effects.

This review aims to provide a focused and up-to-date synthesis of recent studies on black cumin (Nigella sativa) supplementation in broiler chickens. By emphasizing its effects on growth, immunity, gut health, antioxidant activity, and meat quality, this work addresses practical applications and identifies knowledge gaps, providing a targeted perspective that distinguishes it from broader reviews.

2. Effects of Black Cumin on Growth Performance and Feed Efficiency

Numerous studies have investigated the effects of Nigella sativa supplementation on broiler growth performance. Outcomes vary with form of supplementation (seed, meal, oil, nanoemulsion), inclusion level, broiler breed, and environmental conditions. Overall, the evidence suggests that N. sativa exerts dose-dependent and context-dependent effects, functioning more as a performance stabilizer under stress than a universal growth enhancer.

2.1. Effects Under Normal Rearing Conditions

Under standard conditions, moderate supplementation improves body weight gain BWG and feed conversion ratio (FCR), whereas excessive inclusion may reduce feed intake and growth efficiency. Supplementation with 1 and 2% Nigella sativa seeds significantly increased live body weight by week 6 [15]. Diets with 3% or 6% seed meal showed improved final body weight and BWG and FCR, with 3% showing the best response [16]. However, inclusion of 9% black cumin reduced growth, lower feed intake, and poorer feed efficiency, indicating benefits at moderate levels, but adverse effects at excessive inclusion.

Further supporting these findings, broilers supplemented with 0.5% and 1% black cumin seed oil exhibited greater weight gain in the starter (0–14) and finisher (29–42) phase compared to controls (p < 0.05), with FCR significantly decreased in the finisher phase at 1% [11]. Inclusion at 0.5%, 1%, and 1.5% levels during the grower and finisher phase (21–35) significantly increased live weights (p < 0.05) [1]. Growth benefits were most evident in later stages (31–45) with 0.5% and 1.5% oil, while feed intake and FCR remained unaffected [17]. Overall, 1% black cumin seed oil improved growth across 1–45, whereas 0.5%produced the highest production efficiency. At 0.1%, black cumin oil reduced feed intake, likely due to the bitterness, yet still enhanced BWG, final body weight, and FCR [18].

Some studies report phase-specific effects of black cumin on growth and intake. For example, feed intake significantly increased only between days 28–42, potentially attributable to black cumin’s aromatic compounds enhancing palatability [13]. Although there were no significant effects during the starter phase (0–21 days), performance improved significantly (p < 0.05) in the finisher phase (22–42 days) with 1 and 1.5% black cumin supplementation [8]. Similarly, inclusion of 1% and 1.5% black cumin initially caused slight body weight reduction at 14 days but ultimately improved body weight at day 45 across all levels (0.5%, 1% and 1.5%) (p < 0.05), likely due to enhanced nutrient digestibility [2]. Also, dietary inclusion of 0.5% Nigella sativa significantly increased feed intake during the starter phase (1–14 days), whereas 1% reduced it. Over the full trial, feed intake was significantly higher with 0.5% and 1.5% black cumin, but was unchanged with 1% (p < 0.05).

Although some studies reported no significant effects of black cumin on growth performance at low or high inclusion levels [19], others showed greater benefits at moderate to higher inclusion rates. One study found improvements in body weight (p < 0.05), especially with 40 and 60 g/kg of seed meal [14]. All tested levels (20, 40, and 60 g/kg) also significantly improved FCR and reduced mortality.

Under normal conditions, black cumin’s benefits are dose-dependent. Variation among studies reflects differences in supplementation form, inclusion level, and broiler strain.

2.2. Effects Under Heat Stress Conditions

The benefits of black cumin are more pronounced under heat stress. Heat stress reduced BWG and feed intake, while increasing FCR and mortality. Supplementation with black cumin seed powder (5 and 15 g/kg) mitigated these effects, improving BWG and FCR compared with the heat-stressed control (p < 0.01) [20]. Feed consumption was highest at 5 and 15 g/kg, whereas the 10 g/kg group achieved the best FCR and lowest mortality compared to the heat stress group, likely due to improved digestive function and immune modulation. Similarly, 1 and 2% inclusion levels increased final body weight and weight gain under heat stress, while feed intake and FCR decreased [12]. A nanoemulsion of Nigella sativa oil (Nano-NS, 30–50 mg/kg) enhanced the bioavailability of bioactives such as thymoquinone and caryophyllene in heat-stressed broiler birds [21]. Nano-NS at all stages (30, 40, and 50 mg/kg) improved BWG and FCR.

The consistent improvements under heat stress suggest that black cumin acts as a protective agent, helping birds maintain performance by improving digestive efficiency and supporting antioxidant defenses. This indicates its role is more of a stress mitigator than a universal growth promoter.

2.3. Therapeutic Benefits Under Pathogen and Toxin Challenge

Nigella sativa’s growth-promoting effects are more pronounced under infectious or toxic challenges. In a trial with healthy broilers, supplementation with N. sativa oil (1, 2, and 5 mL/kg) did not significantly affect feed efficiency or weight gain [22]. However, under Clostridium perfringens challenge, black cumin oil—particularly at 2 mL/kg—enhanced feed intake compared to infected, untreated controls, while FCR and BWG did not change significantly.

Evidence from seed-based supplementation is more variable. Some studies reported no significant effect of 5% black cumin seeds on necrotic enteritis [23], while others showed a clear benefit. Inclusion of 5% black cumin seed significantly reduced necrotic enteritis lesion scores and mortality rates compared to the untreated positive control group, although the results did not surpass those achieved with antibiotic treatment (bacitracin methylene disalicylate) [22]. These benefits were likely linked to bioactive compounds in black cumin seed oil, particularly thymoquinone, which appeared more effective against a less virulent Clostridium perfringens strain (Cp#6). In addition to its antimicrobial activity, black cumin seed oil improved growth performance, as evidenced by increased BWG and better feed conversion. These findings support the potential use of black cumin seed oil as a natural feed additive to help manage necrotic enteritis and promote overall broiler health.

Dietary inclusion of Nigella sativa seed at 50 g/kg mitigated liver damage caused by aflatoxin exposure in broiler chickens [24]. Supplementation enhanced hepatic expression of aldo-keto reductase family 7 member A2, an enzyme involved in detoxification, restored levels of nuclear factor erythroid 2-related factor 2, a key regulator for antioxidant responses, and reduced caspase-3 activity, a marker of apoptosis. These effects collectively contributed to improved detoxification capacity, stronger antioxidant defense, and reduced hepatocyte apoptosis, suggesting a hepatoprotective effect.

Protective effects were also evident in bacterial challenge models. Broilers supplemented with 2% N. sativa powder showed a lower FCR over the overall growth period and markedly reduced fecal Escherichia coli counts, while body weight gain and final body weight were not significantly affected [25]. Likewise, 2% N. sativa powder improved feed intake, weight gain, and FCR in broilers challenged with Pasteurella multocida, compared with the infected unsupplemented control, although performance did not reach the level of uninfected birds [26].

Collectively, these findings suggest that the growth-promoting effects of N. sativa are limited in healthy flocks but become more evident under stress conditions, where supplementation helps mitigate performance losses associated with pathogens or toxins and may serve as a natural alternative to antibiotic growth promoters.

2.4. Mechanistic Insights and Performance Variability Analysis

The growth-promoting effects of Nigella sativa are attributed to its bioactive constituents. Ethyl ether extracts of black cumin have been linked to enhanced weight gain [1,13], while the antioxidant properties of seed meal act as natural growth promoters, further boosting performance [1]. Thymoquinone, the primary active compound of black cumin, comprising approximately 60–80% of the essential oil (0.5–1.6% of the seed), is believed to play a central role in these effects [14]. Furthermore, black cumin seed oil increases the energy density of broiler diets, which may contribute to improved growth and performance outcomes [11]. Essential oil components such as anethole may stimulate the secretion of digestive enzymes and bile acids, thereby enhancing nutrient absorption [20]. Notably, phytosterol compounds in black cumin have been shown to inhibit micelle formation by affecting bile acid absorption, potentially improving metabolic efficiency [27].

While black cumin shows promising mechanisms for enhancing performance, in vivo responses remain inconsistent. Under standard commercial rearing conditions without intentional heat stress, feeding Cobb chickens 10% black cumin seed meal for 35 days showed no significant differences in body weight compared to controls [28]. This highlights the influence of factors such as experimental design (open housing [28]), breed, diet, or management conditions. Similarly, a trial conducted during the summer/monsoon season in Nagaland, India, found no significant effects on average body weight, feed intake, FCR, or carcass yield [29].

Variations in outcomes across studies may partly result from differences in broiler breed, black cumin forms, and dosages. For example, studies using Ross-308 (e.g., [11,14]) or Cobb strains (e.g., [28,30]) showed different responses, suggesting breed-specific differences in feed efficiency or tolerance to phytogenic compounds. Performance results also varied depending on forms, ground seeds, seed meal, or seed oil, with evidence indicating that seed oil may improve production efficiency more consistently at moderate doses. Dose-dependent effects were observed, with excessive supplementation (e.g., 8–16%) often negatively impacting feed conversion or growth [19], whereas supplementation at 1–2% generally enhanced performance [15]. These findings highlight the importance of considering formulation strategies, strain-specific responses, and optimal inclusion rates when evaluating black cumin’s role in broiler production.

3. Effects of Black Cumin on Immune Function and Blood Chemistry

3.1. Immune Modulation

Black cumin exerts notable effects on both immune responses in broilers, particularly on antibody titers and leukocyte profile. Several studies report consistently enhanced immune function at moderate levels of supplementation. For example, 1% black cumin seeds in Ross-308 significantly increased Newcastle disease (ND) antibody titers compared to the vaccinated control, whereas higher levels (16%) suppressed immune responses, indicating a dose-dependent effect [19]. In Vencobb-400 broilers supplemented with ground seeds, ND virus-specific antibody titers were particularly increased (p < 0.001) by day 35 [13].

Supplementation with 1.5% Nigella sativa oil in Arbor Acres broiler birds enhanced antibody responses to ND and Infectious Bursal Disease (IBD), suggesting improved immune responsiveness [17]. Lower inclusion level (0.5% and 1.0%) significantly improved IBD antibody titers but did not affect ND titers. In Ross-308 broilers supplemented with black cumin seed meal, immunoglobulin G and M increased at all levels (20, 40, and 60 g/kg), whereas immunoglobulin A levels and lymphocyte counts were elevated at only 60 g/kg; black cumin also decreased heterophil counts and the heterophil-to-lymphocyte ratio at 60 g/kg, reflecting a significant improvement in immune status (p < 0.05) [14]. Nigella sativa meal also positively influenced organ development related to immunity and digestion in broilers [16]. The bursa of Fabricius weight increased significantly at 3% and 6% but not at 9%, while all levels increased gizzard weight, suggesting better digestive capacity. Chickens fed Nano-NS at 40 and 50 mg/kg showed significantly decreased serum IL-6 and TNF-α, increased IgG and IgA, and higher thymus and bursa weight, whereas IL-10, IgM, and spleen weight were unaffected [21].

Black cumin improves humoral and cellular immunity in a dose- and form-dependent manner, with nanoemulsion forms enhancing bioavailability and immune outcomes at lower doses.

3.2. Hematological Parameters

Beyond immune modulation, black cumin also influences hematological profiles in broilers. High inclusion levels (up to 16%) elevated red blood cell (RBC) counts, packed cell volume (PCV), and hemoglobin (Hb), while reducing white blood cell (WBC) and lymphocyte counts [19]. In contrast, some studies reported increases in both WBC and lymphocytes at 60 g/kg [14]. These discrepancies may reflect differences in experimental design, housing, or the forms of black cumin used, such as seed meal [14], versus whole seeds [19].

Additionally, broilers fed diets containing 2% Nigella sativa had significantly elevated serum globulin levels, supporting enhanced immune function [15]. These findings align with other reports of immune-modulatory effects, though the exact responses appear dose- and form-dependent. Moderate supplementation (3% and 6%) significantly reduced serum total cholesterol and low-density lipoprotein (LDL) while increasing high-density lipoprotein (HDL), whereas higher inclusion (9%) lowered total cholesterol and LDL but did not affect HDL, indicating moderate supplementation is most effective [16]. Similarly, nano-NS at 50 mg/kg significantly increased serum HDL and decreased LDL and total cholesterol [21]. All levels of black cumin seed supplementation (1%, 2%, and 3%) increased both LDL and HDL cholesterol levels and decreased plasma cholesterol levels in broilers compared to the control group [29].

Moderate doses enhance immune-supportive hematology and improve lipid profiles and liver function, while excessive levels may have suppressive or undesirable metabolic effects.

3.3. Liver Enzyme and Metabolic Health

In terms of liver enzymes and functions, moderate supplementation (up to 2%) improved blood albumin, total protein, glucose, calcium, phosphorus, and alanine aminotransferase (ALT) levels [19]. In contrast, higher inclusion levels (4–16%) reduced these parameters but significantly lowered cholesterol, triglycerides, alkaline phosphatase (ALP), and aspartate aminotransferase (AST), indicating a dose-dependent effect. Similarly, dietary black cumin seed powder supplementation at all levels (5,10, and 15 g/kg) reduced heat stress-induced elevation in key blood enzymes (ALT, AST, ALP) and lipid levels (triglycerides, cholesterol), suggesting a protective effect on metabolic health [20]. Broilers with 3% and 6% black cumin had increased serum albumin levels, indicating enhanced liver function and protein metabolism, whereas benefits were absent at 9%, highlighting the importance of optimal dosing [16].

In another study, supplementation at 40 and 60 g/kg increased RBC counts, hemoglobin, and hematocrit while lowering serum ALP [14]. In Vencobb broilers, black cumin seed powder elevated serum protein levels (p < 0.05) and reduced triglycerides and cholesterol [8]. The cholesterol-lowering effects may be attributed to its phytochemical composition, particularly its sterol content. Compounds such as β-sitosterol have been shown to inhibit dietary cholesterol absorption [8,27,31].

3.4. Contradictory Findings and Potential Explanations

It is important to note, however, that not all studies observed changes in blood chemistry. Some reported no significant differences in hematological or biochemical parameters following black cumin supplementation; the variability in outcomes is likely influenced by factors such as dosage, bird strain, and environmental conditions.

While globulin levels increased with 2% Nigella sativa, indicating enhanced immunity, triglyceride levels peaked at 3%, potentially reflecting undesirable metabolic effects [15]. This underscores the need for caution at higher inclusion levels.

Understanding dose, form, strain, and environmental context is essential for optimizing the immune and metabolic benefits of black cumin in broilers.

4. Effect of Black Cumin on Gut Health and Microbiome

Black cumin improves intestinal morphology and microbial balance, supporting nutrient absorption and health, though effects depend on form and inclusion level.

4.1. Improvement in Intestinal Morphology

Several studies have highlighted the positive effects of black cumin on gut morphology and microbial balance in broilers. For example, broilers supplemented with black cumin showed improvement in intestinal structure, particularly in the jejunum (villus height, villus area, and villus height to crypt ratio)—the main site of nutrient absorption [30]. Villus area increased across all inclusion levels (5, 10, 15, and 20 g/kg), with 10 g/kg supplementation producing a significantly improved villus height-to-crypt depth ratio (p ≤ 0.05). In the ileum, villus height was significantly increased at 20 g/kg (p ≤ 0.05).

Black cumin also reduced villus width, crypt depth, and villus surface area in the ileum, with a tendency toward reduced villus height [13]. These changes indicate notable morphological changes in the region. Duodenal and jejunal morphology was unaffected—except for a trend toward a reduced villus height-to-crypt depth ratio in the duodenum. These results suggest that while black cumin selectively influences ileal structure, its impact on the morphology of the upper small intestine is minimal. Overall, these findings support the potential safe and selective antimicrobial effects of black cumin’s bioactive compounds; further studies are needed to validate these effects.

Black cumin selectively enhances ileal and jejunal structure, supporting nutrient absorption while minimizing adverse intestinal remodeling.

4.2. Modulation of Microbiota

Supplementation at 20 g/kg black cumin significantly promoted the growth of beneficial bacteria like Lactobacillus in the ileum, where lower levels (5, 10, and 15 g/kg) did not show consistent effects [30]. Coliform counts were largely unaffected, indicating selective enhancement of beneficial bacteria without disrupting overall microbial balance.

In a six-week experiment, dietary black cumin seed meal at 40 and 60 g/kg markedly reduced harmful microbial populations in the cecum, including coliforms and Escherichia coli (p < 0.05), while all tested levels (20, 40, 60 g/kg) significantly reduced cecal yeast and mold counts (p < 0.05) [14]. Lactobacillus abundance remained unaffected, suggesting a selective antimicrobial effect that targets harmful microbes while sparing beneficial ones. Nano-NS supplementation at 50 mg/kg significantly increased Lactobacillus, decreased E. coli, and slightly reduced C. perfringens, with 40 mg/kg also effective in Lactobacillus and E. coli [21]. Similarly, black cumin-supplemented groups reduced Salmonella spp. without affecting E. coli, Lactobacillus spp., and Clostridium spp. (p = 0.04) [13], further supporting its selective antimicrobial action.

4.3. Variable Responses Based on Form and Inclusion Level

Some studies report differential effects of black cumin. Supplementation with 10% seed meal in Cobb broiler chicks significantly reduced cecal microbial populations, including both beneficial and harmful bacteria such as Enterobacteriaceae and Escherichia coli, while other taxa (e.g., Clostridioides difficile, Roseburia, and Streptococcus) were unaffected at day 35 [28]. Black cumin oil supplementation has also been shown to reduce the ileal total bacterial count, coliforms, E. coli, and Salmonella, demonstrating its potential as a natural alternative to antibiotics for enhancing growth and poultry health [32].

Black cumin functions as a precision feed additive, stabilizing performance and health through dose- and form-specific strategies while supporting growth, immunity, and gut integrity.

5. Black Cumin on Antioxidant and Anti-Inflammatory Properties

5.1. Enhancement of Antioxidant Status

Black cumin supplementation enhances antioxidant status in broilers. Broilers supplemented with 60 g/kg of black cumin showed elevated levels of key antioxidant enzymes—glutathione peroxidase (GSH-Px), total superoxide dismutase (T-SOD), and catalase (CAT) in the serum, along with reduced malondialdehyde (MDA) levels in the liver [14]. Supplementation with 40 or 60 g/kg also significantly increased GSH-Px in the liver and breast meat and T-SOD in the liver (p < 0.05).

Consistently, black cumin reduced MDA levels compared to controls, indicating reduced lipid peroxidation, while enhancing SOD and GSH-Px activities, suggesting enhanced neutralization of reactive oxygen species [12]. Nano-NS supplementation significantly increased SOD and decreased MDA, without affecting glucose or triglycerides [21]. Similarly, black cumin seed oil at 0.5%, 1.0%, and 1.5% significantly increased SOD activity, while 1.5% also enhanced glutathione (GSH), and 1.0% improved GH-Px and glutathione reductase (GRx) activities, indicating dose-dependent enhancement of antioxidant enzymes, particularly under heat stress conditions [17]. Additionally, black cumin seed supplementation improved antioxidant status in broiler serum, contributing to overall health [13].

5.2. Reduction in Inflammatory Responses

Black cumin seed supplementation exhibits anti-inflammatory effects in broilers. Heat stress significantly increased pro-inflammatory cytokines (IL-6, TNF-α) and decreased anti-inflammatory IL-10 in both serum and liver of broilers. Supplementation with 15 g/kg mitigated these effects under heat stress: significantly increasing IL-10 and decreasing IL-6 and TNF-α in serum, while in the liver, IL-10 increased significantly, but IL-6 and TNF-α were not significantly altered [20]. These results indicate dose-dependent immunomodulatory effects, particularly in heat-stress–induced birds. These birds also exhibited enhanced antioxidant enzyme activity (GPx, SOD, and CAT) and reduced MDA levels in the serum, liver, and spleen, while TNF-α and IL-6 showed no significant changes.

The anti-inflammatory properties of black cumin are attributed mainly to thymoquinone, one of the principal constituents of its seed.

6. Effects of Black Cumin on Meat and Carcass Quality

6.1. Meat Quality Improvements

Several studies have examined the impact of black cumin seed (Nigella sativa) supplementation on the meat of broiler chickens. Broilers supplemented with 60 g/kg of black cumin seed meal showed significantly higher breast meat pH and dry matter content compared to controls [14]. Supplementation at 40 and 60 g/kg also increased crude protein, ash, and total volatile base nitrogen levels in breast meat, while all supplementation levels significantly reduced breast meat lipid content (p < 0.05). Additionally, black cumin increased the yellowness in breast meat at all doses, likely due to natural pigments or antioxidants. Broilers fed 40 and 60 g/kg also showed reduced lightness, more reddish color, and better sensory qualities such as juiciness, tenderness, taste, and aroma compared to the control (p < 0.05). Similarly, black cumin supplementation raised meat pH, which is associated with better tenderness [12]. It also increased redness and yellowness and reduced lightness in meat color, attributed to black cumin’s antioxidant properties that help preserve muscle pigments. Similarly, dietary black cumin seed oil significantly improved the fatty acid profile of breast meat by reducing saturated fatty acids and increasing unsaturated fatty acids [11].

6.2. Carcass Composition and Fat Reduction

Several studies have reported reductions in abdominal fat and carcass lipid content with black cumin supplementation. Supplementation at 1.0% and 1.5% significantly reduced abdominal fat percentage, carcass fat, and meat cholesterol levels, although meat yield and dressing percentage were unaffected [8]. At 1.5%, breast meat and drumstick percentages increased significantly (p < 0.05), while skin percentage and abdominal fat decreased, with no changes in average live weight, dressing yield, and organ weights [1]. Supplementation at 15 and 20 g/kg diets significantly improved carcass dressing percentage at 27 days, while no effect was observed at 47 days [30]. Similarly, black cumin oil supplementation resulted in the highest dressing percentage among the treatments [18]. Nano-NS at 40 and 50 mg/kg increased dressing percentage, although other carcass traits remained unaffected [21].

Reductions in liver and abdominal weights were observed at 28 days, with no changes in other organs. By day 45, supplementation at 0.5, 1, and 1.5% increased carcass weight percentage, while the Bursa of Fabricius and heart weight increased only at 1% and 1.5%, and proventriculus weight improved at 1.5% [2]. Black cumin seeds enhanced protein deposition, especially in thigh muscles, potentially reflecting improved intestinal protein utilization [13].

Black cumin seed oil, rich in unsaturated fatty acids, contributes to healthier meat by increasing beneficial fatty acids in breast meat [11]. Dietary black cumin seed meal also significantly reduces MDA and lipid peroxidation levels in breast muscle, likely by mitigating endogenous lipid oxidation [14]. The supplementation demonstrates a lipolytic effect, shown by significant reductions in abdominal fat and higher yields of breast and drumstick meat, contributing to overall live weight and slaughter weight gains [1]. Lastly, the essential oil of black cumin seed, containing approximately 60% thymoquinone alongside carvone, anethole, carvacrol, and 4-terpineol, exhibits potent antioxidant activity and stimulates digestive enzyme secretion in the intestinal mucosa and pancreas [8,31].

Black cumin supplementation enhances meat quality, improves carcass composition, reduces fat deposition, and protects against lipid oxidation, particularly at moderate doses and in bioavailable forms, making it a valuable natural feed additive.

7. Limitations

Although numerous studies highlight the positive effects of black cumin (Nigella sativa) supplementation on broiler chicken performance, several limitations must be noted. First, this review focuses exclusively on broiler chickens and does not include studies on layer hens or other poultry species, so the conclusions should not be generalized to all chickens. Moreover, the number of peer-reviewed studies available is relatively limited, restricting the depth of analysis in each functional category. There is also considerable heterogeneity among the reviewed studies in terms of supplementation form (e.g., whole seed, seed oil, ground seed, or meal), dosage levels, duration of supplementation, and experimental conditions. This variability complicates direct comparisons and limits the ability to draw definitive conclusions on specific criteria. For instance, while some studies used common commercial strains like Ross-308 or Cobb-500, others lacked breed specification or used less common strains, possibly influencing physiological responses and performance outcomes.

In addition, high levels of black cumin seed meal may change the nutrient profile of the diet, potentially affecting protein and energy balance if not properly formulated; this factor was not consistently reported or controlled across studies. Many studies were conducted using a limited number of commercial broiler breeds, which may reduce statistical power and increase variability or bias in outcomes. Furthermore, despite the promising findings, the overall number of high-quality, peer-reviewed studies remains limited, particularly studies involving long-term supplementation or large-scale trials under commercial production conditions. Finally, some studies report inconsistent or non-significant results, underscoring the need for standardized protocols, larger sample sizes, and independent replication to improve reproducibility and confidence in the conclusions.

Table 1. Key characteristics of studies investigating the effects of black cumin (Nigella sativa) supplementation in broiler chickens. The table summarizes the breed or strain, the number of birds used, the form of black cumin administered (e.g., seeds, seed meal, seed powder, oil), and the duration of each experiment.

Study	Breed/Strain	Number of Birds	Forms of Black Cumin	Duration of the Experiment (Days)
Abdollahi et al. [30]	Cobb 500	420	Grounded seeds	49
Talebi et al. [19]	Ross-308	160	Seeds	42
Fathi et al. [14]	Ross-308	400	Black cumin seed meal	42
Kumar et al. [13]	Vencobb-400	360	Grounded seeds	42
Demirci et al. [11]	Ross-308	108	Seeds oil	42
Jahan et al. [1]	Cobb 500	144	Black cumin seed meal	35
Attia and Al-Harthi [17]	Arbor Acres	175	Seed oil	45
Fathi et al. [20]	Ross-308	500	Seed powder	42
Singh and Kumar [8]	Vencobb	150	Seed powder	42
Hassan and Mandour [2]	Arbor Acres	140	Seeds	45
Rahman and Kim [12]	Not mentioned	200	Seeds	35
Zaazaa et al. [28]	Cobb	600	Black cumin seed meal	35
Devi et al. [29]	Cobb 400	120	Seed powder	42
El-kashef [16]	Hubbard	120	Black cumin seed meal	42
Qader et al. [15]	Ross-308	240	seeds	42
Ragab et al. [18]	Cobb 500	140	Cold-pressed seed oil	38
Manjunatha et al. [22]	Cobb 500	384 (Trial 1), 320 (Trial 2)	Seeds oil	28
Manjunatha et al. [23]	Cobb 500	384	Seeds	28
Elbaz et al. [21]	Ross-308	375	Nano-NS	35
Ates et al. [24]	Ross	100	seeds	28
Haq et al. [25]	Ross-500	400	Seed powder	35
Raheem et al. [26]	Arbor Acres	100	Seed powder	49

Note: All studies included day-old chicks at the start of the experiments.

summarizes key characteristics of the studies investigating black cumin (Nigella sativa) supplementation in broiler chickens, including breed or strain, sample size, form of black cumin used, and duration of the experiments. These variables highlight the diversity in experimental designs, which contributes to the variability of reported outcomes.

8. Conclusions

Black cumin (Nigella sativa) supplementation offers multiple benefits for broiler chickens, including improved growth performance, feed efficiency, immune responses, and meat quality. These benefits make black cumin a compelling alternative to synthetic growth promoters and antibiotics, aligning with sustainable and residue-free poultry production. The main findings of this review paper are summarized in Figure 1, highlighting the key impacts of black cumin supplementation in broiler chickens. However, the variability in study designs, broiler genotypes, supplementation forms, and dosages highlight the need for more standardized and large-scale in-depth research. Future investigations should also assess the long-term safety, economic feasibility, and practical application of black cumin under commercial production conditions with particular emphasis on breed comparisons, dosage optimization, and cost–benefit analyses to fully establish its role and feasibility in sustainable poultry farming.