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Thermotolerance in Hair Sheep and Sustainable Strategies for Heat Stress Mitigation

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Karen Mariela Valadez-García, Porfirio Nicolás-López, Ulises Macías-Cruz and Leonel Avendaño-Reyes

Submitted: 13 June 2026 Reviewed: 30 June 2026 Published: 18 August 2026

DOI: 10.5772/intechopen.1017009

Postmodern Livestock Management - Innovations and Sustainable Practices IntechOpen
Postmodern Livestock Management - Innovations and Sustainable Practices Edited by Akbar Nikkhah

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Postmodern Livestock Management - Innovations and Sustainable Practices [Working Title]

Dr. Akbar Nikkhah

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Abstract

In light of the expanding global population, increasing demand for meat, and the intensifying challenge of global warming, hair sheep offer a promising strategy to enhance food security due to their high feed efficiency and thermotolerance. The thermoresistance observed in hair sheep is attributed to specific phenotypic traits that facilitate efficient heat dissipation, as well as biological responses such as respiratory evaporation, increased insulin sensitivity, enhanced erythrocyte oxygen-carrying capacity, and prevention of tissue catabolism and oxidative damage. While these thermoregulatory and cytoprotective mechanisms effectively restore normothermia without compromising feed intake, carcass yield, or meat quality, hair sheep demonstrate increased energy expenditure for thermoregulation, reduced energy allocation to growth, and may experience oxidative stress. Consequently, mitigating heat stress (HS) in hair sheep necessitates an integrated approach that combines sustainable nutritional and management practices to reinforce thermoregulatory and antioxidant mechanisms, thereby improving thermoresistance and growth performance. Nutritional interventions to alleviate HS in sheep include adjusting feeding frequency and schedule, reducing dietary fiber, and incorporating additives that enhance dietary energy density, vitamins, minerals, and natural antioxidants. Management strategies involve providing shade, fans, and fresh water, managing flocks during the coolest periods of the day, and implementing silvopastoral systems. Nevertheless, further research is required on supplementation with plant-derived secondary metabolites, manipulation of the rumen environment, and the application of precision livestock tools in hair sheep raised in warm production systems. Accordingly, this chapter describes the mechanisms of thermoregulation in hair sheep and examines sustainable strategies and future perspectives for mitigating HS in this species.

Keywords

  • food safety
  • sheep meat
  • thermoregulation mechanisms
  • nutritional strategies for heat mitigation
  • nonnutritional strategies for heat mitigation

1. Introduction

Global livestock farming faces two major challenges: rising demand for animal protein and climate change. As a result, all countries require more efficient production systems [1]. These challenges are of global significance because they threaten the sustainability of food systems and directly impact the livelihoods and nutritional security of growing populations worldwide. In this sense, farmers and researchers are focused on identifying and implementing effective animal production strategies, such as selecting species and breeds that efficiently convert feed into meat and adapt to current climatic conditions [2]. Hair sheep are notable for their feeding efficiency and heat resistance. Their adaptability allows them to thrive in environments where other breeds may struggle, thereby supporting consistent meat production even under adverse conditions [3]. By providing sustainable protein sources in regions particularly vulnerable to environmental stress, hair sheep not only help address local food security issues but also support broader efforts to secure global protein supplies. Therefore, hair sheep represent a valuable genetic resource for efficient use of natural resources, with the potential to significantly enhance food security as livestock industries adapt to these worldwide challenges.

Compared to wool breeds and other domestic species, hair sheep are heat-resistant and can continue to grow and reproduce in the extreme conditions of arid and semi-arid zones [4]. This resilience stems from phenotypic, physiological, metabolic, and cellular adaptations that enhance tolerance to high temperatures [5–8]. Hair sheep primarily dissipate heat through increased respiration, which allows them to eliminate up to 70% of their body heat via evaporation. Under prolonged or extreme heat, they also make metabolic adjustments, such as reduced thyroid activity and increased tissue insulin sensitivity, without changing cortisol levels. Additional cellular adaptations include larger erythrocytes, greater oxygen-carrying capacity, and the release of chaperone heat shock protein (HSP) proteins [8], which help prevent tissue damage. These thermoregulatory mechanisms enable hair sheep to withstand high temperatures without reducing feed intake or significantly affecting productivity, carcass yield, or meat quality [6]. Strengthening these mechanisms will further improve the efficiency of hair sheep meat production under heat stress (HS).

The reduction in growth rate caused by HS in hair sheep highlights the need for technologies to mitigate its negative effects on meat production. Since feed intake remains stable at high temperatures, dietary adjustments for heat-stressed fattening sheep can address their increased maintenance nutritional needs [9]. Current research explores ways to improve growth and carcass traits in warm environments by increasing energy and protein density or by adding vitamins, minerals, or natural antioxidant supplements [9, 10]. Beyond nutrition, it is essential to prevent excessive HS by providing artificial or natural shade [11], establishing appropriate grazing and handling schedules, and ensuring comfortable, uncrowded spaces [12]. Effective management and feeding practices will enhance hair sheep’s ability to thermoregulate and maintain productivity under high temperatures. Consequently, integrating these strategies is crucial for sustaining efficient and resilient meat production in hair sheep facing challenging thermal conditions.

2. Hair sheep, facing global meat demand and climate change

Global patterns of population growth, urbanization, and increased purchasing power in developing countries have led to a marked increase in worldwide demand for meat [1]. As meat consumption is projected to grow by 47.9 million tons over the next decade, understanding how this demand will be met is increasingly critical. Annual per capita consumption is projected to increase by 0.9 kg per capita per year (edible retail weight equivalent) by 2034 [2]. To address this rising demand, more than two-thirds of additional meat production is expected to come from chicken (51%) and pork (28%), while beef and lamb will account for only 15% and 6%, respectively. Notably, global demand for lamb is projected to increase by 20% by 2029 compared with the current production of 9.9 million tons. The majority of this increase will be supplied by China, Australia, and New Zealand, currently the main producers of sheep meat, as well as by economically vulnerable countries in Asia and Africa [3]. Therefore, examining the adaptation of sheep production systems in these regions is essential to ensuring both food security and sustainable livestock development in the context of changing global and regional demand.

Furthermore, most of the world’s land area has arid bioclimatic conditions, a situation that is expected to worsen in the coming years. According to the current Köppen climate classification [13], approximately one-third of the Earth’s surface is arid, with the remainder classified as cold (25%), tropical (22%), temperate (16%), and polar (7%). However, this bioclimatic distribution is changing because of global warming. Specifically, the proportion of hot and dry regions is projected to increase this century due to elevated atmospheric greenhouse gas (GHG) concentrations, resulting in global warming [14]. Thus, under a high-GHG-emissions scenario, the global surface temperature could increase by 2 °C by 2040 and by up to 5 °C by 2100 compared with the 1850–1900 period [15]. As a result of these temperature increases, arid zones will expand by approximately 115 km2 per decade, and both high and low temperatures will intensify across all climatic regions [16].

Given this global scenario, although sheep and goat meat contribute the least to global production, they will remain the main sources of animal protein in marginalized environments. According to the latest official figures [3], the global sheep population is over 1.26 billion head, concentrated mainly in countries in Asia (43%) and Africa (33%), which are characterized by low development and a high prevalence of undernourishment (1–3). While this distribution limits the development of global sheep farming due to a lack of inputs and technology, for food-deficient countries, sheep will continue to be an alternative for combating hunger and generating income [17]. This is why, from the 1950s to the present, researchers and producers have focused on selecting native wool and hair sheep breeds, as well as Creole genotypes, which, due to their ability to adapt to different agroecological zones and production systems [18], guarantee meat production [2].

In the face of rising ambient temperatures, the heat resistance of hair sheep is of particular importance for meat production. Compared to medium and long-wool breeds from temperate climates, hair sheep and fine-wool producers exhibit a greater capacity to adapt to high temperatures due to the morphological characteristics of size, skin, and hair or wool covering that they have developed because of a process of natural and/or artificial selection [19]. Thus, because of their origin and adaptation to warm climates, hair sheep exhibit phenotypic characteristics such as a higher skin area-to-live-weight ratio, less subcutaneous fat, more sweat glands, and thinner skin [20]. Meanwhile, fine-wool sheep from arid or desert regions have also shown an ability to adapt to desert climatic conditions due to their smaller body size and shorter fleece length (<75 microns) and diameter (19 microns) compared to medium and long-wool breeds [21, 22]. Thus, these phenotypic characteristics reduce thermal insulation and make the thermoregulatory mechanisms of hair and fine-wool sheep more efficient, allowing them to grow and reproduce despite extreme climatic conditions [4, 5, 23]. Considering the above, the resilience of hair and fine-wool sheep breeds to increased ambient temperatures and arid environments underscores their importance for sustainable meat production in regions most vulnerable to climate change [24].

3. Thermoregulatory responses of hair sheep under HS

Sheep are homeothermic animals, meaning they must maintain a constant internal temperature (38.3–39.9 °C) for adequate physiological functioning [25]. To achieve this, sheep must remain within their thermoneutral zone (TZ), which is an ambient temperature range in which they can balance heat production and loss with the lowest energy expenditure [26]. In general, the TZ for sheep is 12–25 °C [10]; however, age, physiological state, production level, genotype, and wool/hair characteristics affect their thermal tolerance threshold [27]. Given their genotype, hair sheep show greater thermoresistance, allowing them to extend their TZ by 15–30 °C [4]. When the temperature is within these limits, the animals are in a thermoneutral environment that allows them to maintain normothermia [28]. Under these thermoneutral conditions, sheep maintain a balance between heat loss and gain through radiation, conduction, and convection [25]. Thus, through these nonevaporative mechanisms, sheep exchange heat with the environment without resorting to water production or evaporation, nor any extra energy expenditure [6]. However, if environmental conditions exceed their upper thermoneutral limit, sheep activate additional and more efficient mechanisms to maintain their internal body temperature (Figure 1).

Increased ambient temperature is detected by cutaneous thermoreceptors, which signal to the central nervous system [29]. As a first response, catecholamines (adrenaline and noradrenaline) are released from the adrenal medulla, thereby promoting the redistribution of blood flow to the periphery to activate nonevaporative heat loss [30]. Because of this redistribution of blood flow, cutaneous radiation becomes the primary pathway for heat dissipation, particularly in highly vascularized anatomical regions and in animals with a greater skin surface area per kilogram of body weight [6, 31, 32]. However, if high temperatures persist or intensify, the thermal gradient between the animal’s skin and the environment decreases, and with it, the efficiency of nonevaporative mechanisms [5]. In response to this, evaporative heat loss, i.e., respiratory evaporation and sweating, is employed. Additionally, metabolic and cellular adjustments are utilized [33].

Figure 1.

Thermoregulation mechanisms of hair sheep in thermoneutral and heat-stress environments.

Under severe HS, hair sheep activate additional physiological thermoregulatory mechanisms. When nonevaporative heat dissipation becomes insufficient, evaporative mechanisms are triggered, primarily through a substantial increase in respiratory rate, which can reach up to six times the normal range [5]. Accelerated breathing, or panting, facilitates the elimination of warm exhaled air as water vapor, enabling the release of up to 70% of body heat [34]. However, this process presents two major risks: dehydration and acidosis, defined as a decrease in blood pH. Dehydration results from excessive loss of electrolytes that regulate fluid balance, such as sodium, chloride, and potassium. Acidosis is linked to increased carbon dioxide exhalation, which is essential for bicarbonate formation, the body’s primary buffer of acidic compounds [35]. To mitigate these risks, hair sheep demonstrate adaptive heterothermy, which allows them to increase their respiratory rate until the temperature gradient with the environment is reduced. During periods of peak solar radiation, sheep tolerate increased body heat load, and as ambient temperatures decline in the afternoon and evening, they exhibit the highest respiratory rates to dissipate accumulated heat [4]. By maintaining elevated respiratory rates for shorter durations, the risks of dehydration, alkalosis, and excessive energy expenditure are minimized [27]. Additionally, sheep adapted to warm climates reduce water loss in feces and urine, increase water intake, and enhance renal reabsorption of osmotically active electrolytes to further prevent dehydration [36].

If hyperthermic conditions intensify or persist, hair sheep further adapt by modifying postabsorptive metabolism, enhancing erythrocyte oxygen-carrying capacity, and activating cytoprotective pathways. A well-documented metabolic response in heat-stressed hair sheep is the reduction of thyroid hormone production, which decreases thermogenic effects [5, 27]. Activation of heat-dissipation pathways increases tissue demand for glucose and oxygen (O2). In response, hair sheep enhance insulin sensitivity, facilitating cellular glucose uptake and maintaining basal cortisol levels, thereby preventing tissue catabolism [8]. Additionally, in the presence of erythrocyte lysis associated with HS [31], these breeds increase erythrocyte size and hemoglobin concentration to sustain a constant O2 supply to cells. At the cellular level, hair sheep upregulate inducible HSPs to minimize cell damage and improve thermotolerance [37]. For example, higher HSP70 expression has been linked to greater mononuclear cell viability and reduced thermoregulation time (RT) in heat-stressed Pelibuey sheep [38]. Similarly, comparisons among Nigerian hair sheep breeds revealed that those with higher serum HSP70 concentrations exhibited lower RT, indicating superior thermoregulatory capacity [39]. Collectively, increased respiratory evaporation, enhanced insulin sensitivity, and improved erythrocyte oxygen-carrying capacity, along with prevention of tissue catabolism and oxidative damage, constitute the primary mechanisms conferring heat resistance in hair sheep. Therefore, implementing strategies that support these mechanisms is essential for maintaining or increasing sheep productivity under HS conditions.

4. HS effects on the meat production of hair sheep

High temperatures present both direct and indirect challenges to sheep meat production [10]. Direct effects include decreased feed intake, impaired rumen function, compromised immune responses, and increased susceptibility to pathogens and emerging diseases associated with climate change [25]. Indirectly, elevated temperatures reduce feed and water availability due to rainfall shortages, droughts, and diminished crop yields. Collectively, these thermal and nutritional stresses decrease animal welfare and limit nutrient availability for essential biological functions in sheep [35]. This results in lower fertility and growth rates, ultimately reducing meat production [40]. The severity of these negative impacts varies according to the adaptive capacity of each breed [23]. Notably, in hair sheep, HS does not significantly impair growth or productivity [4].

During the fattening period, high temperatures reduce growth rate and feed efficiency in hair sheep, although feed intake remains unaffected. In Dorper × Katahdin lambs, studies have reported decreases exceeding 25% in daily weight gain and feed efficiency, which are linked to a 32% increase in maintenance energy expenditure [7, 27]. Conversely, research on Dorper lambs [41, 42] and their crosses with Katahdin [7] and Pelibuey [43] indicates that HS does not impact dry matter intake in hair breeds, likely due to their acclimatization to warm environments. Notably, maintenance of feed intake under HS provides a significant energetic advantage, supporting thermoregulation and, to a lesser extent, ongoing growth [8].

Maintaining feed intake levels prevents hair sheep from mobilizing adipose and muscle tissue and, conversely, allows them to maintain an environment of slow anabolism and postabsorptive metabolism, which is reflected in continuous weight gain and the maintenance of carcass attributes [5–7, 41]. In general, short-term (14 days) or prolonged (>30 days) exposure of hair lambs to EC does not affect carcass weight, performance, conformation, or body fat deposition [7, 40, 43]. Contrary to expectations, Macías-Cruz et al. (2013; 2020) reported a 5% increase in hot carcass yield and a 35% increase in ribeye area in hair sheep lambs under environmental EC, effects that may have been mediated by an increase in insulin sensitivity and cortisol resistance in skeletal muscle [7, 8]. Regarding fat deposition, EC does not affect total internal fat in hair sheep, but it does redistribute fat, increasing it in the renal-pelvic region (KPH) and decreasing it in the omental region [7]. The authors suggested that the lower amount of omental fat may be an adaptation to dissipate heat generated by ruminal activity, while the increased KPH fat, given its high vascularization, ensures rapid energy availability in case of nutritional deficiency.

In general, stress (thermal and nonthermal) has been associated with a high incidence of dark, firm, and dry meat in sheep due to the depletion of muscle glycogen reserves during fattening and, consequently, a final pH ≥6 in the meat [40, 44]. However, data available to date on meat from hair sheep breeds demonstrate that, although stress decreases water-holding capacity and increases final pH, luminosity, hue, color intensity, saturation, and shearing effort, these attributes remain within reference values without compromising quality [7, 40]. In fact, high values of color parameters indicate brighter, more appealing meat for consumers. According to Macías-Cruz et al. [7], this may be associated with the thermoresistance of these breeds and a possible increase in type IIa muscle fibers, which are characterized by lower susceptibility to HS, high myoglobin content, good aerobic activity, and high glycogen content. However, this latter hypothesis still requires confirmation.

Taken together, the studies demonstrate that high temperatures do not negatively affect meat production in hair sheep. While HS reduces daily weight gain and feed efficiency due to lower energy availability for growth, this is partially offset by the maintenance of feed intake and adjustments in postabsorptive metabolism (i.e., increased insulin sensitivity and cortisol resistance) [7, 8]. Therefore, establishing strategies to reinforce these responses will improve the efficiency of hair sheep for meat production under HS.

5. Nutritional sustainable strategies for mitigating HS in hair sheep

The reduction in growth rate due to HS in hair sheep presents an opportunity to develop technologies that partially or fully mitigate its negative effects on sheep meat production. Because feed intake is not affected by high temperatures, manipulating the diet of heat-stressed fattening sheep could be a mitigation strategy to meet additional nutritional maintenance needs. Accordingly, a wide variety of studies are currently being conducted to improve the growth and carcass characteristics of fattening sheep in warm environments by increasing energy and protein density or by including dietary additives [9, 10].

5.1 Modifications in feeding management

Simple, cost-effective adjustments to feeding programs can reduce the body heat load in sheep and improve energy availability for growth [44–46]. Under extreme heat, sheep generally decrease feed intake and spend more time lying down during periods of peak solar radiation. However, hair sheep breeds compensate for this reduction by significantly increasing feed intake at night and in the early morning, resulting in an average daily intake comparable to that under normal conditions [47]. In this context, providing high-quality feed during cooler periods of the day or increasing feeding frequency can help reduce metabolic heat generated by feed intake during the hottest hours [48]. For example, Chagas et al. [46] found that in Santa Inés lambs, feed intake and feed conversion ratio decreased when feeding was shifted to the afternoon, with better outcomes at 6:00 PM compared to 3:00 PM. Similarly, Abozed et al. [49] reported that lambs in arid Egyptian conditions fed three times daily (8:00 AM, 1:00 PM, and 6:00 PM) exhibited higher average daily gain and a lower feed conversion ratio compared to those fed twice daily (8:00 AM and 1:00 PM). In addition, management practices that support higher feed intake in hot environments include placing feeders and waterers in shaded areas and providing dietary supplements and high-quality water [9].

5.2 Nutritional modification of the diet

Increasing dietary energy density is a consistent strategy for mitigating HS in fattening sheep. These animals require additional available energy for maintenance, which is typically derived from dietary energy allocated to growth or from the catabolism of fat or muscle tissue [50]. Traditionally, increasing the inclusion of fermentable carbohydrates has been used to raise the energy density of fattening diets [8]. However, such diets can elevate endogenous heat production and increase the risk of rumen disorders [9]. For this reason, supplementation with alternative energy sources and gluconeogenic compounds is being evaluated for lambs under HS. Halakoo et al. [51] demonstrated that, in heat-stressed wool lambs, dietary addition of bypass fat, beef tallow, or canola oil reduces feed conversion ratio and increases serum glucose concentration. Additionally, the inclusion of gluconeogenic precursors increases feed intake and decreases feed conversion ratio in Afshari lambs exposed to HS [50]. Recent findings [52] indicate that, in Dorper x Katahdin lambs exposed to outdoor HS, supplementation with thiamine diphosphate, a glucogenic cofactor derived from vitamin B1, improves dietary energy efficiency for growth and carcass mass deposition in ewe lambs but not in males. Thiamine also increases heat loss through the body surface, regardless of gender.

In addition to increasing energy intake, other dietary adjustments for heat-stressed sheep include reducing fiber intake to minimize the internal heat generated by digestion. Sheep fed high-fiber diets exhibit greater metabolic heat production associated with higher levels of ruminal acetate [9]. On the other hand, if energy is limited, a protein inclusion percentage similar to or higher than that provided under normal conditions increases maintenance energy expenditure to eliminate excess nitrogen as urea [8]. Therefore, lambs subjected to extreme conditions should consume diets with a low percentage of neutral detergent fiber and ensure higher energy density rather than a higher protein intake [25, 35]. However, under these environmental conditions, the fiber requirements and protein-to-energy ratio of these breeds have not yet been established.

Mineral supplementation is another critical consideration in diets for heat-stressed sheep [53]. Increased respiratory rate for thermoregulation and, to a lesser extent, sweating can alter mineral levels in these animals [54]. Therefore, diets should include mineral supplements to prevent acid–base imbalance and reduce the risk of respiratory alkalosis. In this regard, research in ruminants indicates that dietary electrolytes benefit animals under HS conditions [55–57]. The inclusion of electrolytes helps restore acid-base balance disrupted by hyperthermia [8] and increases both dry matter intake and ruminal pH by enhancing ruminal stability through their buffering capacity [54, 58]. However, the available information on this topic remains limited for hair sheep.

5.3 Antioxidant supplementation

HS promotes oxidative stress; that is, it generates excessive amounts of reactive oxygen species and reduces antioxidant defenses in organisms. Therefore, dietary supplementation or direct intramuscular administration of antioxidants can improve growth in heat-stressed lambs [59]. Currently, there is evidence of improved growth, metabolism, and thermoregulation capacity resulting from the inclusion of vitamins and minerals with antioxidant activity in the diet or their intramuscular administration in sheep.

Several authors have proposed that dietary supplementation with vitamin E and selenium improves thermoregulation capacity [59–63]. This, in turn, enhances antioxidant capacity and boosts metabolism [64–68]. Together, they help reduce the oxidative stress index and increase the cellular antioxidant response [69]. Additionally, in skeletal muscle, both antioxidants modulate the expression of HSP70, proinflammatory cytokines, and the transcription factor NF-κB, thereby decreasing the oxidative damage caused by EC in swine [70].

In the search for sustainable alternatives, some phytochemicals and herbs have attracted interest for their potential to enhance sheep production in warm environments, owing to their potent antioxidant activity [71] and effects on feed intake and digestibility [54]. Accordingly, studies in heat-stressed lambs have shown that phenolic compounds and carotenoids improve production parameters due to their reducing power and ability to stimulate antioxidant enzyme responses [72, 73]. In Awassi lambs exposed to high temperatures (38.5 °C), supplementation with 1.0 and 7.0 g of naringin increased average daily gain, feed efficiency, and final live weight, which was attributed to greater activity of the superoxide dismutase and glutathione peroxidase enzymes, as well as higher serum concentrations of albumin and immunoglobulins [74]. Similar enzymatic, immunological, and growth results were reported in heat-stressed lambs supplemented with turmeric extract, a compound rich in phenols [73].

Also, tannin supplementation in Ujumqin lambs during the summer improved the overall antioxidant response and increased average daily gain (13%) and feed efficiency (14%) in liver and muscle tissue [72]. Both tannins and the carotenoid lycopene have proven effective in preventing lipid peroxidation and maintaining color stability in the fresh meat of wool lambs exposed to HS [72, 74, 75]. In heat-stressed Dorper × Katahdin lambs, the phenolic compound ferulic acid enhanced feedlot performance under extreme HS and increased internal fat reserves and muscle mass deposition in muscles involved in breathing by preventing protein oxidation [76]. Taken together, these results demonstrate that dietary supplementation with antioxidant phytochemicals is a sound nutritional strategy for improving lamb meat production under HS; however, no information on this topic was found for heat-stressed hair lambs.

6. Alternative nonnutritional approaches to mitigate HS in hair sheep

In addition to nutritional interventions, implementing appropriate facility and management strategies can effectively reduce the body heat load in hair sheep. The most basic form of protection for animals raised outdoors is the provision of shade structures to shield them against solar radiation. However, shade should not completely cover the lamb feedlot, as partial coverage facilitates the dissipation of heat accumulated during the day and released at night [11]. The orientation of the shade, particularly in an east-west direction, is also important because it maintains the shadow beneath the roof during the hottest midday hours [77]. Another sustainable approach involves the use of silvopastoral systems. Recent studies [12] have demonstrated that sheep managed within silvopastoral systems in semi-arid regions experience lower black globe humidity index values and ambient temperatures, which correspond to reduced sheep respiratory rates and rectal temperatures.

Ventilation is also essential for facilitating thermal exchange between the animal’s body surface and the environment. Evidence indicates that, under outdoor HS, lambs cooled by fans during the warmest hours of the day exhibit smaller increases in respiratory rate and rectal temperature. These physiological benefits are associated with a 15% increase in average daily gain [78]. Additional strategies include providing ad libitum access to clean, fresh water and scheduling management practices, such as moving, transporting, or working animals, exclusively during the coolest hours of the day to minimize physical stress.

7. Perspectives on hair sheep production

Oxidative stress and inflammation resulting from HS can damage critical cell types, particularly blood, rumen, and intestinal cells. Consequently, supplementation with secondary metabolites or herbal compounds is increasingly recognized as an effective strategy to improve health status and growth in heat-stressed sheep by supporting the function of blood and rumen cells [73, 79]. Additionally, certain plant-derived secondary metabolites activate growth-promoting pathways. For instance, the phenolic compound ferulic acid has been shown to enhance muscle deposition in pigs under thermoneutral conditions and in hair cattle and sheep exposed to HS, potentially through a β-adrenergic effect [80] and activation of the Sirt/AMPK/PGC-α pathway in oxidative muscle fibers [81]. Other natural compounds may also modulate energy metabolism and stimulate growth by enhancing insulin sensitivity [82], increasing resistance to muscle fatigue, and upregulating the expression of genes associated with myogenesis, growth (Igf1r), and antioxidant response (Nrf2) [83, 84] during fattening and postslaughter periods [85, 86]. Collectively, these findings underscore the potential of investigating herbal products and their metabolites as a promising research direction for identifying natural compounds that enhance muscle deposition and improve meat quality in hair sheep under environmental HS.

Greater attention must be directed toward specific aspects of ruminal function and the ecosystem in heat-stressed hair sheep. Although heat-stressed hair sheep do not alter their feed intake [7], the effects of elevated temperatures on feed fermentation and the absorption of volatile fatty acids in the rumen remain unclear. HS is associated with reduced rumen motility and increased intraruminal temperature, which results in lower volatile fatty acid production and a decreased acetate-to-propionate ratio [9, 35]. However, these effects have not been investigated in heat-stressed hair lambs. Monitoring ruminal temperature and motility in heat-stressed hair sheep will enable researchers to assess the impact of high ambient temperatures on ruminal function and to identify dietary ingredients that regulate intestinal transit and supply the additional 32% energy required for thermoregulation [8, 9] without causing excessive ruminal heat. In addition, microbiota control is a critical component of ruminal microbiota management. Livestock production is both a major contributor to and a victim of global warming, since domestic animals, particularly ruminants, emit significant methane, a GHG associated with HS [14]. Therefore, microbiome interventions, such as feed additives, microbiome engineering, and fermentation modulation, that reduce enteric methane emissions and improve feed efficiency are necessary in heat-stressed sheep [87–89].

Digital technologies and data analytics are transforming livestock production. Precision livestock farming incorporates information technology to continuously monitor and manage livestock, thereby enhancing animal health, welfare, and productivity [90]. Given these advantages, precision livestock farming tools offer significant support for livestock production systems facing HS [91]. Current applications include monitoring bioclimatic conditions such as temperature, humidity, and radiation. The scope of precision livestock farming could be expanded to include body sensors, such as ruminal boluses, rumination collars, and thermal imaging cameras, as well as behavioral sensors, which are valuable for identifying heat-resistant animals [92]. Precision livestock farming also enables greater environmental control by regulating cooling systems, including ventilation, shading, and intelligent misting, and activating them only under critical conditions. In intensive and technologically advanced production systems, these applications are essential for optimizing resource use, particularly through automated drinking and feeding systems [93]. Overall, precision livestock farming is poised to play a pivotal role in physiological and productive monitoring, efficient resource management, and informed decision-making within production systems operating under adverse weather conditions.

8. Conclusions

Hair sheep are projected to become one of the most viable species for meat production within sustainable agricultural systems. In response to increasing global demand and the challenges posed by climate change, the livestock sector must enhance meat production through strategies that are environmentally, economically, and socially sustainable. Compared with other breeds and wool sheep, hair sheep are expected to play a more significant role due to their capacity to activate physiological, metabolic, and cellular thermoregulatory mechanisms that support growth and reproduction in regions with extreme climates. As a result, these breeds represent a valuable genetic resource for the efficient use of natural resources, while also contributing to the profitability of production systems and ensuring a stable meat supply. To realize this potential, it is essential to further strengthen thermoregulatory mechanisms in hair sheep, meet their macro and micronutrient requirements, and mitigate the adverse biological effects of HS through practical, sustainable management strategies.

Conflict of Interest

The authors declare no conflict of interest.

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Karen Mariela Valadez-García, Porfirio Nicolás-López, Ulises Macías-Cruz and Leonel Avendaño-Reyes

Submitted: 13 June 2026 Reviewed: 30 June 2026 Published: 18 August 2026

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