Environmental Enrichment in Dairy Small Ruminants: A PRISMA-Based Review on Welfare Implications and Future Research Directions

Abstract

Background: Environmental enrichment is a promising strategy to improve the welfare of dairy goats and sheep. However, studies in this field remain scattered, and its effects on productivity are unclear. Objectives: To evaluate the effects of environmental enrichment on behavioral, physiological, and productive parameters in dairy goats and sheep. Data sources: Scopus and Web of Science were searched for studies published from 2010 to 2025. Study eligibility criteria: Experimental or observational peer-reviewed studies comparing enriched vs. non-enriched housing in dairy goats or sheep, reporting on welfare or productivity outcomes. Methods: This review followed PRISMA 2020 guidelines and the PICO framework. Two independent reviewers screened and extracted data. Risk of bias was assessed with the SYRCLE tool. Results: Thirteen studies were included, mostly with goats. Physical, sensory, and social enrichments showed benefits for behavior (e.g., activity, fewer stereotypies) and stress physiology. However, results varied by social rank, enrichment type, and physiological stage. Only three studies assessed productive parameters (weight gain in kids/lambs); none evaluated milk yield or quality. Limitations: Most studies had small samples and short durations. No meta-analysis was conducted due to heterogeneity. Conclusions: Environmental enrichment can benefit the welfare of dairy goats and sheep. However, evidence on productivity is scarce. Long-term studies are needed to evaluate its cost-effectiveness and potential impacts on milk yield and reproductive performance.

1. Introduction

Dairy small ruminants, such as goats and sheep, play a vital role in milk production across various regions of the world, especially in smallholder and extensive farming systems [1]. Despite their importance, the welfare of these animals has received relatively less attention compared to dairy cattle, whose management practices have been more extensively studied [2]. In natural environments, animals are exposed to a rich variety of stimuli that vary over time and space. This complexity favors the expression of species-specific behaviors and supports psychological well-being [3,4]. In contrast, intensive farming systems are primarily designed to meet basic physiological needs, such as food, water, and rest, often lacking the environmental stimuli necessary for behavioral and emotional fulfillment [5]. As a result, animals in such systems may be unable to express positive behaviors, such as social play, exploration, and environmental control. This deprivation can lead to boredom, frustration, and a general decline in quality of life [6,7].

Production systems for small ruminants vary widely, from pasture-based extensive models to semi-intensive and fully confined facilities. In more intensive systems, welfare concerns are heightened due to limited space, environmental monotony, and higher incidence of abnormal behaviors such as stereotypies and aggression [2,7]. The absence of adequate stimuli in these environments inhibits natural behaviors and may lead to chronic stress, with negative repercussions for health and productivity [4,5]. Environmental complexity is therefore a key factor in promoting positive welfare outcomes. Housing conditions can range from barren individual pens to enriched group environments that better accommodate natural behaviors [8]. In this context, environmental enrichment aims to meet both ethological and psychological needs by reducing stress and monotony associated with confinement, supporting neurological development, enhancing cognitive and emotional capacities, and promoting resilience by increasing the frequency of positive affective states [3,6].

Environmental enrichment refers to any modification in the animal’s environment that enhances its physical and psychological well-being by promoting the expression of species-specific behaviors [3,4,9]. Therefore, effective enrichment strategies must be grounded in a deep understanding of the species’ behavioral repertoire, cognitive abilities, and sensory preferences. These interventions may include manipulable objects (e.g., ropes, balls, or logs) [10,11], structural elements (e.g., elevated platforms, climbing structures) [11,12,13], sensory stimulation (e.g., tactile, olfactory or auditory stimuli) [9,14,15], feeding devices that prolong foraging behavior [16], and opportunities for positive social interactions. Additionally, human–animal interactions—especially those characterized by gentle handling—can enrich the social environment and enhance animal welfare outcomes [17,18].

Although both goats and sheep are small ruminants, they differ considerably in their behavioral tendencies and environmental needs, making it essential that the design of effective enrichment protocols considers species-specific behavioral traits. While both goats and sheep are social, grazing ruminants, their behavioral profiles differ markedly. Goats are more exploratory, agile, and motivated to interact with their surroundings. They exhibit strong preferences for climbing, jumping, and investigating novel objects, which reflect their ancestral adaptation to mountainous and variable terrain. In contrast, sheep are more neophobic and flock-oriented, typically avoiding novelty and relying more heavily on group cohesion and visual contact with conspecifics. They tend to benefit more from social stability and predictable environments [19,20,21,22]. These distinctions underscore the importance of tailoring enrichment approaches to the ethological needs of each species, rather than adopting a one-size-fits-all model.

From a productive standpoint, animal welfare is directly linked to zootechnical performance. Animals kept in enriched environments tend to exhibit lower physiological stress [9], better feed efficiency [23], and higher milk production and quality [15], as well as stronger immune responses [24] and improved maternal care [25,26]. However, studies specifically focused on environmental enrichment in dairy small ruminants remain scarce, revealing a significant gap in the scientific literature.

Given these considerations, environmental enrichment emerges as a promising strategy to improve both the welfare and productivity of dairy goats and sheep. Nonetheless, the scarcity of targeted studies underscores the need for a systematic review to consolidate existing knowledge, evaluate effective enrichment practices, and identify priority research gaps. Therefore, the aim of this review is to critically examine the scientific literature on environmental enrichment for dairy small ruminants, evaluating the types of enrichment employed, their impacts on behavioral and physiological welfare indicators, and their implications for zootechnical performance.

2. Methods

This systematic review was conducted in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines [27], and synthesizes experimental evidence from the past 15 years to assess the effects of environmental enrichment interventions on the welfare and productivity of dairy small ruminants. The protocol for this systematic review was preregistered on the Open Science Framework and is publicly available at https://doi.org/10.17605/OSF.IO/JNZFK (accessed on 4 July 2025).

Using the PICO framework, the following research question was formulated: In dairy goats and sheep (Population), does environmental enrichment—including structural enrichment (e.g., toys, platforms, climbing objects), sensory enrichment (e.g., auditory stimuli like music, visual or olfactory stimuli), feeding enrichment (e.g., provision of forage or challenging foods that stimulate foraging behavior), social enrichment (e.g., increased social contact, stable groups), cognitive enrichment (e.g., food puzzles, training), and gentle handling (Intervention)—compared to conventional housing without enrichment (standard or barren environments) and minimal or aversive handling (Comparison), affect productive parameters (milk yield and quality, reproductive performance) or welfare indicators (natural behaviors, occurrence of abnormal/stereotypic behaviors, physiological stress markers, cortisol, oxidative metabolites, health, injury incidence, immune parameters, body condition score, among others) (Outcomes)?

2.1. Search Strategy (Databases, Descriptors, and Keywords)

A comprehensive literature search was conducted in two major databases, Scopus and Web of Science, to identify articles published between 2010 and 2025. These databases were selected for their broad indexing of peer-reviewed, high-impact journals, advanced search functionalities, and multidisciplinary coverage—key for retrieving relevant and high-quality studies.

To avoid selection bias, inclusion and exclusion criteria were defined before the literature search. The search focused on studies addressing environmental enrichment in dairy goats or sheep and used free-text terms combined with Boolean operators. Boolean operators (AND/OR) were employed to combine terms related to the population, intervention, and outcomes. Broad outcome-related terms (e.g., welfare, behavior, stress indicators, milk production) were included to refine the results, although the main filtering was applied during screening based on eligibility criteria.

Searches were performed in the title, abstract, and keyword fields. All search terms were in English (publications in other languages were excluded based on our criteria). Synonyms and spelling variations—including differences between British and American English (e.g., behavior vs. behaviour)—were considered. This strategy ensured the retrieval of relevant studies regardless of regional linguistic variations.

The search results were imported into a reference management tool (Mendeley), and duplicates were removed before screening. Filters were applied during the search when available: language, publication year, and relevant subject categories (animal science, veterinary medicine). Additionally, reference lists of selected articles were screened to identify further eligible studies.

Table 1. Search Terms and Strategy by Database.

Concept	Search Terms
Population	“dairy goats”, “dairy sheep”, “small ruminants”, “caprines”, “ovines” (Also the scientific names Capra aegagrus hircus and Ovis aries in some of the searches)
Intervention	“environmental enrichment”, “enrichment devices”, “sensory enrichment”, “social enrichment”, “feeding enrichment”, “cognitive enrichment”, “gentle handling”
Welfare Outcomes	“animal welfare”, “well-being”, “behavior”, “behaviour”, “stress indicators”, “cortisol”, “health”
Productivity Outcomes	“milk production”, “milk yield”, “productivity”, “milk quality”, “milk composition”

details the specific search strategies used for each database.

2.2. Eligibility Criteria

2.2.1. Inclusion Criteria

Studies were included if they met the following criteria: (a) published within the last 15 years (2010–2025), to capture current research, as the search was conducted in 2025; (b) published in English, to ensure reliable interpretation of methodology and results; (c) peer-reviewed works, including articles in scientific journals, peer-reviewed conference proceedings, or book chapters; (d) comparative experimental or observational designs explicitly assessing environmental enrichment versus a non-enriched control group, measuring animal welfare variables (behavior, stress physiology, health) and/or productive outcomes (milk yield and quality); (e) focused on dairy small ruminants, including goats or sheep in lactation or dry periods, or closely related models (e.g., growing kids/lambs under dairy systems or males of dairy breeds), as long as relevant outcomes were measured (e.g., post-weaning weight gain related to future milk production).

2.2.2. Exclusion Criteria

The following were excluded: (a) studies outside the defined time range or not published in English; (b) review articles (used as theoretical background but not considered primary studies in the systematic review); (c) studies without a clear control group or that did not assess environmental enrichment (e.g., studies focused solely on nutritional enrichment without environmental relevance, or management practices not related to enrichment); (d) studies focused on other species, unless separate results for goats or sheep were presented, which did not occur during screening; (e) non-peer-reviewed grey literature (technical reports, unpublished theses, popular science articles, etc.), except when strictly necessary and highly relevant (none were ultimately included); (f) duplicates of already included studies (in case of overlapping records across databases, only one entry was kept).

2.3. Study Selection and Data Extraction (PRISMA Protocol)

The initial search strategy, combining only the intervention-related terms (“environmental enrichment” OR “enrichment devices” OR “sensory enrichment” OR “social enrichment” OR “feeding enrichment”), generated a large volume of references. After combining with population-related terms (“dairy goats” OR “dairy sheep” OR “small ruminants” OR caprines OR ovines), the search was significantly refined. Finally, by combining intervention, population, and outcome-related terms (welfare and productivity), only articles relevant to the study were retrieved (

Table 2. Quantification of articles based on basic and combined descriptors, searched on the Scopus and Web of Science platforms from 2010 to 2025.

Database	Descriptors and Boolean Operators	Number of Studies
Scopus	TITLE-ABS-KEY (“environmental enrichment” OR “enrichment devices” OR “sensory enrichment” OR “social enrichment” OR “feeding enrichment”)	5838
	TITLE-ABS-KEY ((“environmental enrichment” OR “enrichment devices” OR “sensory enrichment” OR “social enrichment” OR “feeding enrichment” OR “cognitive enrichment” OR “gentle handling”) AND (“dairy goats” OR “dairy sheep” OR “small ruminants” OR caprines OR ovines))	9
	TITLE-ABS-KEY ((“environmental enrichment” OR “enrichment devices” OR “sensory enrichment” OR “social enrichment” OR “feeding enrichment” OR “cognitive enrichment” OR “gentle handling”) AND (“dairy goats” OR “dairy sheep” OR “small ruminants” OR caprines OR ovines) AND (“animal welfare” OR well-being OR behavior OR “stress indicators” OR cortisol OR health))	7
	TITLE-ABS-KEY ((“environmental enrichment” OR “enrichment devices” OR “sensory enrichment” OR “social enrichment” OR “feeding enrichment” OR “cognitive enrichment” OR “gentle handling”) AND (“dairy goats” OR “dairy sheep” OR “small ruminants” OR caprines OR ovines) AND (“milk production” OR “milk yield” OR productivity OR “milk quality” OR “milk composition”))	2
Web of Science	TITLE-ABS-KEY (“environmental enrichment” OR “enrichment devices” OR “sensory enrichment” OR “social enrichment” OR “feeding enrichment” OR “cognitive enrichment” OR “gentle handling”)	6205
	TITLE-ABS-KEY ((“environmental enrichment” OR “enrichment devices” OR “sensory enrichment” OR “social enrichment” OR “feeding enrichment” OR “cognitive enrichment” OR “gentle handling”) AND (“dairy goats” OR “dairy sheep” OR “small ruminants” OR caprines OR ovines))	15
	TITLE-ABS-KEY ((“environmental enrichment” OR “enrichment devices” OR “sensory enrichment” OR “social enrichment” OR “feeding enrichment” OR “cognitive enrichment” OR “gentle handling”) AND (“dairy goats” OR “dairy sheep” OR “small ruminants” OR caprines OR ovines) AND (“animal welfare” OR well-being OR behavior OR “stress indicators” OR cortisol OR health))	13
	TITLE-ABS-KEY ((“environmental enrichment” OR “enrichment devices” OR “sensory enrichment” OR “social enrichment” OR “feeding enrichment” OR “cognitive enrichment” OR “gentle handling”) AND (“dairy goats” OR “dairy sheep” OR “small ruminants” OR caprines OR ovines) AND (“milk production” OR “milk yield” OR productivity OR “milk quality” OR “milk composition”))	2

).

As a starting point for the identification phase, the combination of terms related to the intervention and the population was used, resulting in 24 articles (Scopus, n = 9; Web of Science, n = 15). After removing duplicates (records retrieved from both databases), 18 unique references remained for evaluation. Next, a screening of titles and abstracts was carried out, and ten studies were excluded at this stage for not meeting the inclusion criteria. Thus, eight full texts were assessed for eligibility, and all met the inclusion criteria (

Table 3. Studies included in the systematic review on environmental enrichment in dairy goats and sheep, with main characteristics and findings (ordered by year of publication).

Authors (Year)	Country	Species (Subjects)	Type of Enrichment	Variables Evaluated	Main Results
Coulon et al. (2011) [17]	Norway	Pregnant Norwegian-Dala ewes and their lambs. (n = 23 ewes, 23 lambs) Duration—5-week ewe treatment exposure; 3-day lamb testing at 25–34 days old.	Social enrichment—gentle vs. aversive handling during gestation.	Heart rate variability, fear responses, and cognitive performance in lambs after birth.	Aversive handling of pregnant ewes led to more passive and fearful behavior in their lambs, and lower vagal tone, without affecting their cognitive performance.
Bøe et al. (2012) [28]	Norway	Lactating Norwegian goats (n = 82) Duration—23 days of enclosure access, 19 with enrichment.	Physical enrichment—outdoor access and additional enrichment (e.g., branches).	Space use, resting behavior, and activity.	Goats preferred the outdoor enclosure for activity, with branches serving as attractive enrichment. Social activity decreased, but aggression increased—possibly due to resource defense or more play-fighting in the enriched space.
Miranda-de Lama et al. (2013) [16]	Mexico	Lactating Saanen goats (n = 24) Duration—80 days to assess dominance status; 33-day study: 17 days with enrichment, 16 days with handling tests.	Physical and nutritional enrichment—food presentation, physical barriers, and elevated areas.	Reactivity behaviors (distance to handler, reactivity to capture and physical restraint) and plasma cortisol.	Environmental enrichment increased cortisol levels and influenced goats’ behavior during handling by enhancing reactivity, vigilance, and aggressiveness, particularly in relation to social rank.
Rosas-Trigueros et al. (2017) [10]	Mexico	Male French-Alpine suckling kids (n = 20) Duration—41 to 44 days (until animals reached ~10 kg body weight).	Physical enrichment—elevated sacks of henequen, trunks, tires and coconuts.	Adrenal glands histology, plasma cortisol, weight gain.	No significant differences were found in cortisol levels or weight gain between groups. However, histological differences in adrenal zones suggested increased adrenal activity in animals from non-enriched environments.
Gomes et al. (2018) [11]	Brazil	Lactating Saanen goats (n = 12) Duration—10-day experimental period, preceded by 7-day pre-experimental phase.	Physical enrichment—Hanging and floor PET bottles filled with corn (visual and auditory stimuli), fixed wall brushes, suspended tire, and a tree trunk for climbing.	Natural behaviors, social interactions, stereotypies, aggression, object use.	Enriched goats were more active and exhibited fewer stereotypies. Although fights were more frequent in enriched pens due to object competition, goats engaged more in self-grooming. The suspended tire and tree trunk were the most used objects, especially for bipedal postures.
Nascimento et al. (2022) [14]	Brazil	Lactating Saanen goats (n = 12) Duration—78 days total: 3-day control + five 15-day enrichment phases.	Physical and sensorial enrichment—music; PET bottles with corn; tires; logs of wood.	Thermoregulatory (body temperature, respiratory rate), behavioral responses.	Environmental enrichment improves thermoregulatory and behavioral responses, especially with multiple objects offered simultaneously.
Wein et al. (2024) [9]	Israel	Lactating and dry Saanen x Nubian goats (n = 24) Duration—30-day adaptation + 2 × 10-day treatment periods (cross-over design).	Physical enrichment—static scratch brushes and wooden stage.	Stress-related indicators (cortisol, serotonin, oxytocin, oxidative stress markers, pro-inflammatory cytokines).	Environmental enrichment with scratch brushes benefited dry goats by reducing stress and inflammation but had adverse effects in lactating goats, increasing stress markers. Enrichment strategies should consider the animals’ physiological stage.
Cowie (2025) [12]	New Zealand	East Friesian Lacaune dairy ewe lambs (n = 54) Duration—7 days of exposure to enrichment or control during the first week of artificial rearing.	Physical enrichment –balls, ropes, bottles, bath puffs, strings, chairs, tables and platforms.	Weight gain	Providing physical enrichment with varied objects improved weight gain in precociously weaned lambs, suggesting that such intervention can reduce stress and support welfare during the initial phase of artificial rearing.

). However, an additional five studies were included after a complementary search conducted in the same two databases (Scopus and Web of Science). These studies addressed interventions such as the use of partition walls or gentle handling, which are consistent with the concept of environmental enrichment. Additionally, some relevant studies involving dairy breed lambs were not retrieved in the initial search because they used the term lambs instead of sheep or ewes in the title, abstract, or keywords. As a result, these studies were not previously retrieved based on the search descriptors but were included in the results and discussion due to their relevance to the topic (

Table 4. Additional studies included in the systematic review on environmental enrichment in dairy goats and sheep, with main characteristics and findings (ordered by year of publication).

Authors (Year)	Country	Species (Subjects)	Type of Enrichment	Variables Evaluated	Main Results
Ehrlenbruch et al. (2010) [29]	Norway	Pregnant Norwegian goats (n = 24) Duration—4-week trial with 3-day habituation in a Latin Square rotation.	Physical enrichment—additional walls in the resting area.	Resting behavior, general activity, preference for wall contact, social interactions.	Additional walls in the resting area increased goats’ use of wall support during rest but did not affect total resting time or aggressiveness.
Baxter et al. (2016) [18]	United Kingdom	Primiparous pregnant Saanen × Toggenburg goats and their kids (n = 40 goats; 76 kids) Duration—71-day study: 5-week handling period (days 80–115 of gestation), 35 days until kidding, and 1-day postnatal monitoring.	Social enrichment—gentle, aversive or minimal handling during gestation.	Placental morphology, goats and kids’ behaviors, salivary cortisol, faecal glucocorticoid metabolites and colostrum quality.	Aversive handling during gestation increased maternal stress in goats, caused fetal loss, impaired placental quality, and reduced maternal care after birth. Their offspring showed delayed development, taking longer to stand, suckle, and begin playing.
Oesterwind et al. (2016) [13]	Germany	5 weeks old Nigerian Dwarf goats (n = 34) Duration—71-day study: 6-week shaping phase followed by 3 cognitive enrichment tasks (14 days each).	Physical and cognitive enrichment—straw, climbing rack, round feeder, hayrack, learning device dispensing water rewards.	Learning performance, fear tests, salivary cortisol.	The combination of structural and cognitive enrichment improved performance in learning tasks and promoted positive behaviors in novel or challenging situations, without affecting salivary cortisol levels.
Kakarash et al. (2021) [30]	Iraq	Meriz goats (without mention of the physiological stage) (n = 16) Duration—20-day study: 5-day pre-experimental period for ethogram creation, followed by 15-day behavioral evaluation.	Physical enrichment—canopy, brush, tire, trunk of tree, and plastic PET bottle suspended and freely move on the floor.	Behavior, frequency of interaction, daily spent time on objects.	Environmental enrichment significantly improved goats’ behavior and welfare, also reducing stereotypic behaviors by increasing the average time spent interacting with enrichment objects.
Cowie (2024) [31]	New Zealand	East Friesian Lacaune dairy ewe lambs (n = 114) Duration—21 days of exposure to treatment.	Social enrichment—quiet human company.	Mortality, weight gain.	Human social contact reduced mortality but had no effect on growth performance.

, Figure 1).

For each included study, the following data were systematically extracted: author(s), year, country of origin, species and animal category (goat/sheep breed, lactation or growth stage), type of environmental enrichment tested, main variables evaluated (behavioral, physiological, productive), and key findings related to the effects of enrichment.

Additionally, the methodological quality of the included studies was assessed using the SYRCLE’s Risk of Bias tool (Systematic Review Centre for Laboratory Animal Experimentation), which is specifically designed for laboratory/experimental animal studies and adapted from systematic reviews in the health field. The assessed domains included generation of the randomization sequence (random allocation of animals to enrichment and control groups), blinding of outcome assessors, selective outcome reporting, among others.

Overall, the methodological quality of the studies ranged from moderate to good. Most experiments employed controlled designs; however, none explicitly reported the use of blinding procedures or truly random allocation of individuals, introducing a certain degree of uncertainty. Furthermore, many studies used relatively small sample sizes (often fewer than 20 animals per group), which is common in research involving medium- and large-sized animals, but requires caution when interpreting the results due to the potential for low statistical power.

Despite these limitations, all included studies were published in peer-reviewed scientific journals and presented designs compatible with the proposed objectives (e.g., use of concurrent control groups and standardized measurement of welfare and productivity indicators), ensuring an acceptable level of evidence for the present synthesis.

3. Results

Summary of Included Studies

Of the 13 studies included, 10 focused on goats (Capra hircus), highlighting a more developed body of literature on environmental enrichment in this species compared to dairy sheep. Of the three studies involving sheep, only one included ewes; however, even in this case, the primary focus was on the lambs, evaluating the effects of environmental enrichment during gestation on the offspring rather than on the ewes themselves [17]. The other two studies were conducted directly with dairy lambs [12,31], indicating a significant research gap regarding environmental enrichment in dairy sheep. This may be partly due to the fact that a significant portion of sheep milk production occurs in extensive or pastoral systems, where the concept of environmental enrichment is less commonly applied or studied.

Of the thirteen articles found over a 15-year period, three were published in the last year (2024–2025), reflecting a growing concern for the psychological and behavioral welfare of dairy small ruminants, a topic that has gained more visibility only in recent years.

Most experiments were of short duration, typically ranging from 7 to 10 days, e.g., [11,12] to a few weeks, e.g., [10,14,17,28,29]. The populations studied were also diverse, reflecting the broad range of species and productive categories evaluated. Of the ten studies conducted with goats, five involved the Saanen breed [11,14,24] or its crossbreeds [9,18], while the remaining studies focused on other dairy breeds, such as Norwegian [28,29], Meriz [30], Nigerian Dwarf [13], and Alpine [10]. The predominance of the Saanen breed may be explained by its wide global distribution and frequent use in intensive dairy production systems, making it a preferred model in studies requiring greater environmental control. Although Alpine goats are also widely used for dairy purposes and are known for high yields and adaptability, they appear less frequently in such studies. This may be related to the greater variability in the management systems under which they are raised, making standardization more difficult in experimental protocols. In contrast, breeds such as Norwegian, Meriz, and Nigerian are more geographically restricted and are generally kept in traditional or small-scale systems, which may also contribute to their lower representation in the scientific literature on environmental enrichment strategies.

The types of environmental enrichment evaluated in the studies fell into well-defined categories commonly described in the literature: physical or structural enrichment (e.g., manipulable objects, rubber brushes, tires, branches, climbing platforms, and access to outdoor paddocks); sensory enrichment (e.g., auditory stimulation with music or sounds); social enrichment (focused on positive human contact); and cognitive enrichment (learning devices dispensing water rewards) [13]. Three studies evaluated human–animal interactions (gentle, neutral, or aversive), considered important within the social and behavioral domains. Notably, two of these studies involved pregnant females—one with goats, assessing both maternal and offspring responses [18], and another with ewes, focusing on lamb cognitive development [17]. The third study evaluated dairy lambs in terms of mortality and performance outcomes [31].

Across the studies reviewed, physical enrichment was the most frequently employed strategy (n = 10), followed by social (n = 3), sensory (n = 1), nutritional (n = 1), and cognitive (n = 1). Some studies tested more than one type of enrichment in combination, aiming to enhance the animals’ overall stimulation and welfare. Nearly all studies assessed outcomes related to animal welfare, such as behavior (n = 9). Behavioral indicators included locomotor activity, environmental exploration, social interaction, and responses in human approach tests. Physiological measures were also widely used, with cortisol being the most frequent biomarker [9,10,13,16,18], alongside others like oxidative stress markers and pro-inflammatory cytokines [9], respiratory and heart rates, body temperature [14,17], and adrenal gland histology [10].

Three studies assessed performance outcomes, all involving lambs or kids, focusing on weight gain. No studies directly measured fertility rates or reproductive performance in females, likely due to the short duration of most trials. However, one study did evaluate placental morphology and fetal losses in pregnant goats, which are indirectly related to reproductive performance [18]. This lone study found that evaluated milk production in goats was excluded in the screening phase due to multiple inconsistencies throughout the text, including contradictions between reported results and the authors’ conclusions.

Several studies also reported significant positive behavioral effects associated with enrichment. In a study with lactating Saanen goats, ref. [11] observed that animals housed in an enriched environment (e.g., PET bottles with corn, climbing trunks, tires, and brushes) exhibited greater activity, natural postures (such as bipedal stance), and fewer stereotypies. Similarly, [30] documented active interaction with enrichment items (tires and tree trunks) in Meriz goats, resulting in a reduction in repetitive behaviors. Young Nigerian Dwarf goats exposed to both structural and cognitive enrichment performed better in learning tasks and exhibited greater exploratory behavior in unfamiliar environments, indicating enhanced adaptive capacity [13].

As for physiological responses to enrichment, results varied according to species and physiological stage. For instance, ref. [9] found that fixed brushes reduced cortisol, serotonin, and inflammatory markers in dry goats but paradoxically increased stress indicators in lactating goats. Moreover, studies involving human–animal interaction provided further insight into stress regulation. Aversive handling during gestation in goats led to fetal loss, reduced placental quality, elevated salivary cortisol, impaired maternal behavior, and developmental delays in the offspring [18]. In line with these findings, ref. [17] demonstrated that lambs born to aversively handled pregnant ewes were more passive and had reduced vagal tone, although their cognitive performance remained unaffected.

Additionally, one study evaluated thermoregulatory responses and positive behaviors, observing reduced respiratory rate and body temperature in lactating goats that had access to environmental enrichment [14]. Lastly, only one study [12] directly evaluated the impact of enrichment on growth performance, reporting that precociously weaned dairy lambs housed with diverse physical enrichment items (such as balls, ropes, platforms, and bottles) showed significantly greater weight gain during their first week of artificial rearing.

4. Discussion

4.1. Effects of Environmental Enrichment—Narrative Synthesis of Results

4.1.1. Impacts on Welfare Parameters

Overall, the results were partially divergent, appearing to depend on factors such as the animal’s position within the social hierarchy (social rank), physiological stage, and type of enrichment. While some studies reported behavioral improvements—such as increased activity levels and reduced stereotypies [11,14,28,30]—others observed heightened aggressiveness, reactivity, and vigilance in relation to a handler [16], as well as increased aggression among goats due to competition over enrichment items [11,28]. This finding highlights the importance of careful planning regarding the number of enrichment items available relative to the number of animals, as well as appropriate grouping based on social hierarchy, particularly considering dominant and submissive individuals. For example, ref. [28] observed an average of 23 aggressive interactions over a 5-h period among goats in an enriched outdoor enclosure where approximately four to five branches were provided daily for 82 animals—a ratio of about one branch for every 16 to 20 goats. Although the study did not compare different object-to-animal ratios, the relatively low number of enrichment items may have contributed to the competition and aggressive behavior observed. However, most reviewed studies do not report the proportion or quantity of enrichment items provided in relation to the number of animals, which limits interpretation and could represent valuable information for guiding the development of effective enrichment programs.

The quality of interaction between humans and dairy small ruminants was directly addressed in some studies, revealing that positive handling practices can function as relevant forms of social enrichment. For example, in the study by [16], Saanen goats kept in enriched environments exhibited differentiated responses to handling, with behavioral variations according to social dominance: dominant animals were more evasive and vigilant, while subordinate ones displayed greater aggression. Cortisol concentrations in these groups ranged from 2.3 to 4.8 µg/dL, with dominant animals exhibiting the highest values. The increase in cortisol observed in these animals, although initially interpreted as a stress signal, was discussed by the authors as a possible indicator of arousal or alertness rather than suffering. Meanwhile, ref. [17] demonstrated that gentle handling of pregnant ewes resulted in offspring with lower reactivity and better adaptive behavior after birth, suggesting transgenerational positive effects of a good human–animal relationship. Complementarily, ref. [31] showed that social human contact with orphaned lambs reduced mortality and improved behavioral parameters, reinforcing that consistent and positive human interactions can serve as a relevant enrichment pathway—especially in intensive or artificial management conditions.

Several included studies indicated positive effects of environmental enrichment on physiological stress indicators, although with variations across categories and contexts. In the study conducted by [9], non-lactating goats subjected to physical and sensory enrichment showed significant reductions in markers of oxidative stress and inflammation—such as advanced glycation end products (AGE) and transferrin—as well as hormonal changes indicative of improved well-being, including a 35% increase in serotonin levels (from 150 to 203 ng/mL) and a 42% decrease in AGE levels after 21 days of enrichment. Interestingly, the same protocol applied to lactating goats resulted in opposite responses: elevations in oxytocin and activation of immune pathways suggested that, in this group, enrichment was interpreted more as a strong physiological stimulus than as stress relief. Similarly, in [16], although higher cortisol levels were observed in enriched groups, the authors interpreted these findings as reflective of heightened vigilance or social arousal (especially in dominant animals), not necessarily negative stress. Finally, the study by [10] provided histological evidence of a 22% reduction in adrenal cortex thickness in animals exposed to physical enrichment, suggesting decreased chronic stress despite the absence of changes in fecal cortisol levels. Taken together, the findings reinforce that environmental enrichment can attenuate physiological stress indicators, particularly in conditions of sensory deprivation, although effects may be modulated by factors such as productive stage, type of stimulus, and social context.

One of the most relevant findings in the climatic context was reported by [14], who evaluated dairy goats in the Brazilian semi-arid region exposed to physical enrichments (tires, logs, shaded structures) and sensory stimuli (ambient music). Enriched goats exhibited reduced respiratory rates and body temperatures, suggesting improved thermoregulation and greater ability to cope with heat stress. Mean rectal temperature was reduced from 39.4 °C to 38.7 °C, and respiratory rate dropped from 120 to 85 breaths per minute in enriched animals. These positive physiological effects may reflect both a direct reduction in stress, promoted by a more comfortable and stimulating environment, and adaptive behavioral changes, such as a preference for ventilated areas or more efficient use of space. The results show that simple, low-cost enrichments can significantly contribute to thermal regulation and welfare in hot climates, presenting a promising strategy to mitigate the negative impacts of heat in intensive production systems.

4.1.2. Impacts on Productive Parameters

None of the studies included in this review directly evaluated milk yield or quality in either goats or sheep. Only one study assessed colostrum quality, but it did not report significant effects of environmental enrichment [18]. Additionally, ref [9] demonstrated changes in hormones associated with lactation, such as oxytocin, but did not directly measure productive parameters, limiting inference about real impacts on yield.

No studies involving females directly assessed conception rate, return to estrus, or inter-kidding intervals—parameters that are essential indicators of welfare, as they reflect physiological balance and reproductive success. This highlights an important gap for future research. However, the study by [18] reported findings indirectly related to reproductive performance, as aversive handling during gestation increased maternal stress in goats, caused fetal loss, impaired placental quality, and reduced maternal care after birth. Specifically, 15% of does subjected to rough handling experienced fetal loss, whereas no cases were observed in the positively handled group.

Regarding weight gain, the studies that addressed this variable provided more promising results, especially with suckling lambs or animals under artificial rearing conditions. Ref. [12]. showed that artificially fed dairy lambs exhibited greater growth when housed in enriched environments with platforms and physical stimuli, compared to lambs reared without environmental enrichment. The average daily weight gain was 165 g/day in enriched lambs versus 125 g/day in the control group, over a 45-day period. The results indicate that physical enrichment may enhance physical development by mitigating stress and stimulating natural activity patterns. In contrast, ref. [10] evaluated kids exposed to physical enrichment using elevated sacks of henequen, trunks, tires, and coconuts, and found no significant differences in final weight but reported physiological signs of reduced chronic stress, such as less adrenal gland hypertrophy, which could favor long-term performance.

4.2. Critical Discussion of Evidence

The findings presented above must be interpreted in light of certain methodological and contextual considerations:

• Study Heterogeneity: The studies included in this review show considerable heterogeneity regarding species (goats vs. sheep), breeds, production systems, and types of enrichment evaluated. This diversity limits direct comparability between studies and constrains the possibility of robust, quantitative synthesis. Different enrichment modalities act through distinct mechanisms—for example, auditory stimuli, such as music, influence sensory and emotional pathways [32], whereas physical enrichments, like climbing structures, promote motor and occupational activity. In a study conducted in the Brazilian semi-arid region [14], physical objects had a more pronounced effect on reducing heat stress than music alone, although the latter also contributed to lower surface temperatures. These findings suggest that enrichment effects are stimulus-specific, and that combined approaches, integrating physical, sensory, and social stimuli, tend to produce more comprehensive and consistent welfare responses.
• Individual and Category Differences: The effectiveness of environmental enrichment may significantly depend on the physiological or productive category of the animals. The study by [9] highlighted this variation by comparing lactating and dry goats exposed to the same enrichment protocol. While dry goats showed clearly positive responses—including a 27% decrease in advanced glycation end-products (AGEs), increased serum serotonin levels by 1.8-fold, and improved immune parameters—lactating goats exhibited less favorable or even opposite effects, with increases of up to 15% in cortisol and 22% in oxytocin concentrations. This difference may be related to the high metabolic demands of lactation, which limit animals’ ability to interact with or benefit from additional environmental stimuli. Animals at peak production tend to prioritize feeding and resting behaviors and may show reduced responsiveness to enrichment, or even negative reactions if it interferes with their routine. Conversely, categories such as dry, young, or growing goats have shown greater engagement with physical and sensory enrichments. These findings underscore the importance of tailoring enrichment type and intensity to the productive phase and behavioral needs of each group, to avoid disruption of productive management and to maximize welfare gains.
• Cost vs. Benefit: Despite the animal welfare benefits observed in the included studies, the cost–benefit ratio of environmental enrichment remains a challenge, especially from the producer’s perspective. None of the studies directly evaluated milk production, which is a central focus in dairy farming systems, making it difficult to estimate the economic viability of such interventions. Although environmental enrichment promotes health and positive behavior, it does not always translate into immediate economic returns, which may discourage its adoption by producers in intensive systems. However, the observed 21.3% increase in weight gain during the first week of artificial rearing in enriched dairy lambs (mean: 1.19 kg vs. 0.98 kg in controls), as reported by [12], should be taken into account, as these animals represent future breeding stock and their early development may have long-term impacts on productivity.
• Quality of the Evidence: The quality of the available evidence regarding the effects of environmental enrichment in dairy small ruminants presents important limitations that must be considered when interpreting results. Many of the studies included in this review used relatively small sample sizes (ranging from 12 to 40 animals) or short experimental duration (as short as 7 days and generally not exceeding 45 days), which can limit the detection of subtle or delayed effects. For example, it is widely acknowledged that cortisol has high individual variability, requiring larger samples and more frequent measurements to detect modest physiological changes statistically. In addition, the short duration of some trials limits the ability to assess cumulative effects, such as impact on the full lactation cycle.
• Limitations in Measuring Positive Welfare: Despite methodological advances, the direct measurement of positive welfare remains limited in studies on dairy small ruminants. Most of the research analyzed in this review focused on indicators of stress or the absence of suffering, such as cortisol levels, respiratory rate, or the occurrence of abnormal behaviors. Few studies included variables that reflect positive emotional states or behavioral satisfaction. However, the validation and standardization of specific indicators of positive welfare, such as play, preference for interaction, voluntary use of enrichment objects, or comfort behaviors, are still in their infancy in small ruminants. For instance, only two studies [11,13] reported play behavior or object manipulation frequency, with enriched animals showing up to 3-fold higher exploratory interactions. The lack of consistent protocols makes it difficult to compare studies and reduces sensitivity to detect more subtle emotional benefits. Therefore, future research should focus on developing robust and standardized tools for assessing positive welfare, incorporating, whenever possible, affective, voluntary-choice, and behavioral motivation variables.

4.3. Research Gaps

Several research gaps and opportunities emerged throughout the review:

• Environmental Enrichment in Dairy Sheep: Among the studies analyzed, there is a markedly smaller number of works (n = 3) dedicated specifically to dairy sheep compared to goats. This gap limits the direct applicability of findings, as sheep differ behaviorally from goats: they tend to be more neophobic, less active explorers, and more group-dependent [22]. Thus, extrapolating results from goats to sheep must be done cautiously. Although studies such as [12,17,31] included sheep, the focus was mainly on lambs rather than lactating adult ewes. Future research must therefore specifically address the behavior, physiology, and productive performance of dairy sheep, especially in semi-intensive systems typical of the Mediterranean and South America. Potential approaches include offering manipulable materials in milking pens, shelter structures with thermal and social relevance, or enriched feeding practices during lactation. Expanding this field will support the development of truly species-adapted welfare strategies.
• Long-Term Effects: Most studies in this review evaluated the effects of environmental enrichment over short durations. While some of these experiments demonstrated behavioral and physiological welfare benefits, there remains a significant gap regarding the impacts of long-term enrichment applied continuously throughout a full lactation or over multiple production cycles. No study followed animals over a complete lactation period (generally 150–300 days). Key questions remain unanswered: Would animals in enriched environments show a lower incidence of metabolic diseases? Would they have greater productive longevity? Would reproductive performance improve over subsequent cycles? Such data are crucial to support decisions on the cost-effectiveness of adopting enrichment strategies in commercial production systems.
• Cognitive and Social Enrichment: Despite the diversity of environmental enrichment strategies tested, such as manipulable objects, outdoor access, and sensory stimuli, none of the 13 studies specifically assessed the effects of complex cognitive enrichment, such as the use of food puzzles, learning tasks, or positive reinforcement training. Given goats’ well-documented cognitive abilities [21], this type of stimulation could be a promising way to promote positive emotional states, reduce frustration, and increase environmental engagement, as already demonstrated in other species, particularly in zoo contexts [33,34]. Similarly, social enrichment strategies were rarely addressed in the reviewed studies. Some, such as [12,30], mentioned human social contact or artificial feeding of lambs, but did not delve into structured conspecific social interactions (e.g., stable pairings, time with the mother, or group compatibility). Since both goats and sheep are highly social species, future studies could explore whether social management adjustments, such as creating harmonious groups or supporting stable bonds, can help reduce stress and improve environmental adaptation. Therefore, cognitive and social enrichments remain underexplored areas with great potential to broaden welfare approaches for dairy small ruminants.
• Measures of Positive Welfare: Most of the studies analyzed in this review focused on the reduction of negative welfare indicators. However, a growing trend in animal welfare science proposes a broader focus, one that goes beyond the mitigation of suffering and includes the active promotion of positive emotional states, such as pleasure, contentment, and engagement [35,36,37]. Although some studies indirectly described behaviors compatible with positive welfare, no study directly measured specific indicators of positive emotions, such as vocalizations associated with pleasure, frequency of spontaneous play (“happy hops”), or responses in cognitive bias tests (which assess the tendency to interpret ambiguous stimuli optimistically or pessimistically). The systematic inclusion of these indicators in future studies would allow for a more complete assessment of the effects of environmental enrichment, capturing not only the absence of suffering, but the active presence of well-being. This would represent an important advance in the measurement of animal quality of life, especially in species such as goats and sheep, whose emotional expressiveness may be underestimated by traditional methods.
• Relationship with Zootechnical Parameters: This review makes it clear that relevant gaps remain in the systematic measurement of zootechnical indicators directly related to environmental enrichment. None of the included studies analyzed metrics such as feed conversion, metabolic efficiency, or detailed milk profile (fatty acids, total solids, somatic cell count), which limits understanding of potential indirect productive gains. Considering that chronic stress—often measured by cortisol levels—can affect metabolism and milk quality [38], it would be plausible to assume that enriched animals, by presenting less stress, have a more favorable compositional profile. However, none of the studies directly investigated this hypothesis. This gap represents a promising opportunity for future research that integrates welfare indicators with physical–chemical analyses of milk and zootechnical performance, aiming to connect emotional health, productive physiology, and final product quality.
• Design of Ideal Enrichments: The review also highlights a significant space for innovation in the design and validation of enrichments adaptable to the reality of commercial systems. Only 3 studies out of 13 (23%) described detailed physical or engineering attributes of the enrichment objects used. Developing enriching feeding strategies, such as fiber dispensers or non-caloric treats between milkings, may help stimulate natural behaviors—including rumination—by keeping animals engaged during idle periods, while maintaining their nutritional balance. Such interventions could reduce boredom, stimulate foraging behavior, and improve the overall housing environment. However, this type of approach is still rare in the experimental studies included. The engineering of practical solutions focused on welfare and economic applicability represents an important frontier between science and innovation in the management of dairy goats and sheep.

4.4. Practical Implications and Final Recommendations

Based on the evidence synthesized in this review, a series of practical recommendations can be outlined for producers, technicians, and policy makers, considering both the direct benefits and the limitations observed in the evaluated studies.

• Selection of Safe and Suitable Enrichments: The choice of materials and how they are implemented in the environment should prioritize safety and functionality. The poorly designed enrichments can pose risks, such as udder injuries or traumatic mastitis. It is therefore recommended to start with controlled trials and gradually adjust according to animal response. Body brushes fixed in strategic locations are especially promising, both due to spontaneous acceptance and their beneficial effects on stress markers. Loose objects, such as tires or balls, should be well secured and monitored for hygiene and wear.
• Tailoring by Animal Category: Response to enrichment varies according to physiological stage. Lactating goats, for example, may benefit from gentler, localized stimuli (such as brushes in waiting areas), so as not to interfere with rumination or the milking routine. Animals outside lactation, kids, or growing young animals tend to respond positively to more varied enrichments, such as toys, climbing structures, or light feeding challenges that foster cognitive and motor development.
• Training and Socialization: The integration between environmental enrichment and humane handling is fundamental. Studies indicate that without positive interaction with caregivers, animals may develop avoidance behavior even in enriched environments. Habituation programs and simple positive reinforcement (such as associating caregivers with rewards or carrying out handling calmly and predictably) can be seen as forms of cognitive and social enrichment, improving the human–animal relationship and facilitating procedures such as milking.
• Monitor Long-Term Productive Effects: It is advisable that producers and technical institutions systematically monitor the effects of enrichment over complete productive cycles. The hypothesis that enriched animals show greater productive longevity, lower disease incidence, and better reproductive performance should be investigated in long-term studies, including integrated economic assessments. The collection of such data can provide robust support to justify enrichment as a strategic investment.
• Policies and Welfare Certifications: The consolidation of environmental enrichment as a recommended—or even mandatory—practice can be reinforced by public policies and certification programs. Initiatives such as animal welfare labels can include minimum environmental stimulation requirements (e.g., access to yards, presence of manipulable objects, opportunities for socialization). Regulation based on scientific evidence contributes to the harmonization of productivity, ethics, and sustainability, responding to society’s demands for more responsible production systems.

5. Conclusions

This systematic review highlights the growing scientific interest in the effects of environmental enrichment on the welfare of dairy small ruminants, particularly in the last five years. The analyzed studies demonstrate that physical, cognitive, and social enrichment strategies can positively influence behavioral responses, learning capacity, and stress regulation. However, the findings are not always consistent. Factors such as social hierarchy, physiological stage, and the type and distribution of enrichment elements appear to modulate the outcomes. While several studies reported reduced stereotypies and increased activity levels, others noted undesirable increases in aggressiveness and vigilance, particularly under competitive conditions or among dominant individuals. Furthermore, although none of the studies directly measured fertility rates or milk production—key indicators for assessing economic viability—some findings, such as improved weight gain in dairy lambs and reduced fetal viability under aversive handling, provide indirect evidence of potential long-term impacts on productivity. These results reinforce the relevance of including behavioral parameters in the assessment of animal welfare but also point to important gaps, particularly regarding reproductive performance and cost-effectiveness. Future research should prioritize longer-term trials that integrate performance and economic indicators to better inform the practical application of enrichment strategies in dairy production systems.