Environmental Enrichment in Dairy Small Ruminants: A PRISMA-Based Review on Welfare Implications and Future Research Directions
Abstract
1. Introduction
2. Methods
2.1. Search Strategy (Databases, Descriptors, and Keywords)
2.2. Eligibility Criteria
2.2.1. Inclusion Criteria
2.2.2. Exclusion Criteria
2.3. Study Selection and Data Extraction (PRISMA Protocol)
3. Results
Summary of Included Studies
4. Discussion
4.1. Effects of Environmental Enrichment—Narrative Synthesis of Results
4.1.1. Impacts on Welfare Parameters
4.1.2. Impacts on Productive Parameters
4.2. Critical Discussion of Evidence
- 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
- 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
- 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
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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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” |
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 |
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. |
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. |
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Caldara, F.R.; Buchini, J.L.C.; Garcia, R.G. Environmental Enrichment in Dairy Small Ruminants: A PRISMA-Based Review on Welfare Implications and Future Research Directions. Dairy 2025, 6, 42. https://doi.org/10.3390/dairy6040042
Caldara FR, Buchini JLC, Garcia RG. Environmental Enrichment in Dairy Small Ruminants: A PRISMA-Based Review on Welfare Implications and Future Research Directions. Dairy. 2025; 6(4):42. https://doi.org/10.3390/dairy6040042
Chicago/Turabian StyleCaldara, Fabiana Ribeiro, Jéssica Lucilene Cantarini Buchini, and Rodrigo Garófallo Garcia. 2025. "Environmental Enrichment in Dairy Small Ruminants: A PRISMA-Based Review on Welfare Implications and Future Research Directions" Dairy 6, no. 4: 42. https://doi.org/10.3390/dairy6040042
APA StyleCaldara, F. R., Buchini, J. L. C., & Garcia, R. G. (2025). Environmental Enrichment in Dairy Small Ruminants: A PRISMA-Based Review on Welfare Implications and Future Research Directions. Dairy, 6(4), 42. https://doi.org/10.3390/dairy6040042