Mitigation and animal response to water stress in small ruminants

Abstract

Water stress is usually related to heat stress and decreased feed intake; so its effect is difficult to separate. Small ruminants are able to better adapt to water stress than other species, especially breeds from regions under harsh conditions. Mitigation strategies to water stress will be needed to maintain animal production. Breeding strategies are difficult to implement, and omics technologies are approaches that can help us to unravel the biological mechanisms involved in water stress adaptation. Global climate change is a threat and a major challenge for livestock production because increasing temperatures and reduced water availability decrease forage quantity and quality. The effects of these climate changes are predicted to continue in forthcoming years, which highlight all the problems that water scarcity poses for small ruminant productivity, and for changes in animal physiological, immunological, and ethological aspects. Therefore, the future availability of animal products (e.g., milk, meat, fiber) will also be affected. Small ruminant management based on extensive or semi-extensive systems very much depends on environmental factors like precipitation and climatology. Moreover, water restriction or rationing policies can affect dairy or meat intensive small ruminant production. However, it is important to note that small ruminants can better tolerate water stress than large ruminants or monogastric species as the rumen has been reported to act as a water reservoir in well-adapted sheep (Silanikove, 1994). This water stress tolerance is closely related to breed, and adaptive and indigenous breeds from dry regions are more tolerant than selected breeds. Figure 1 shows a sheep flock of Rasa Aragonesa, a local breed, grazing stubbles in “Los Monegros” a dry region of Aragón (Spain). Sheep Flock of Rasa Aragonesa breed in “Los Monegros”, a dry region of Aragón, Spain. The water requirement of livestock depends on different factors, such as species, diet, size, activity, environmental temperature, and physiological status. Therefore, it is difficult to indicate a specific amount for each species. In a recent trial carried out at CITA Research Center, the average daily water intake of 40 empty Rasa Aragonesa ewes (60 kg of BW) was 2.18 l. These ewes were allocated in individual pens and fed with a total mixed ration under an average temperature of 22 ºC and relative humidity of 56%. The environmental temperature has an important effect on the water intake, in this line Li et al. (2000) observed that ewes drank twice more water under warm (24.8 ºC) than cold (0.4 ºC) temperatures. Under heat stress, crossbreed goats drunk on average 7.4 l (Kaliber et al., 2009) whereas this amount was higher, 15.3 l, in lactating Aardi goats (Alamer, 2009). Therefore, the temperature and lactation status increase the water requirement. It is worth noting that cattle need higher amounts than small ruminants, steers on average drunk 37 liters daily (Ahlberg et al., 2019). Water stress has been less studied in small ruminants than heat stress, which has been extensively investigated, and studies on mitigation and adaptation strategies to water stress are lacking. Within this framework, this paper aims to highlight the main responses and effects of water stress on small ruminants, and the possible strategies that small ruminants can use to mitigate or adapt to water stress. Water stress affects productive traits mainly due to reduced feed intake, which helps to decrease water loss related with feed digestion and metabolism. Additionally, ruminants are able to cumulate water in the forestomach to use as a reserve to face water shortages. Simultaneous to reduced intake, rumen digestive capacity is enhanced by increasing crude protein digestibility (Hussein et al., 2020), but lower dietary energy intake has been recorded. Thus, animals present fat mobilization characterized by increased concentrations of cholesterol and free fatty acids (FFA) in blood, which has been observed in sheep (Jaber et al., 2004) and goats (Kaliber et al., 2016). Evaporation is an important water loss process. It is directly related to metabolic rate and, therefore, the animal metabolic rate is decreased (i.e., heart rate, respiration rate, body temperature) to reduce water loss and to overcome decreased feed intake. Apart from the above-mentioned changes, animals acquire some thermoregulatory behavioral response by not only increasing duration of standing and lying, but also decreasing duration of walking and rumination time, as mechanisms to reduce consumed metabolic energy (Kaliber et al., 2016). These main effects are presented in Figure 2. Physiological changes in sheep and goats under water restriction. When animals suffer mild water restriction, besides the above mentioned adaptive responses, production traits can also be affected, such as reproduction efficiency, growth, and quality of milk and meat. Regarding reproduction, the effect of water restriction on male reproductive traits has been studied by Khnissi et al. (2016) with the Barbarine breed. Those authors showed that the rams which received water only every 4 d had reduced libido, decreased testosterone concentrations and a higher sperm concentration compared with the control rams, but no effects on semen traits were noted. In females, delayed follicular growth, a decrease in estrus response, estrus duration and estradiol in plasma, and increased progesterone have been reported (Naqvi et al., 2017). These outcomes are usually associated with reduced feed intake, which means that it is not simple to separate both effects of reduced water and feed intake on these traits. It is worth noting that some breeds are well-adapted to water deprivation during pregnancy and water deprivation does not alter lambing. Yetisgin and Sen (2020) worked with Awassi ewes and revealed that 50% water restriction reduces body weight (BW), placental weight, and number of cotyledons in pregnant ewes, and birth weights in lambs, but parturition in ewes is successful. This was possible thanks to placental and cotyledon efficiency, which augmented in restricted ewes by the ability to maintain pregnancy in water shortage circumstances. The main effects on reproductivity traits due water restriction are presented in Figure 3. Effects on reproductivity traits in sheep under water restriction conditions. Researchers have paid considerable attention to the effect of water shortage during critical production periods, such as growing and lactating periods, including nutrition status, weight gain, meat quality, and milk secretion decreases with water restriction. Severe water shortage reduces BW upon slaughter, and hot and cold carcass yields, which can affect physio-chemical characteristics, mineral content and the fatty acid profile of meat, whereas dehydration and stress can darken meat color and decrease tenderness (Dos Santos et al., 2019; Akinmoladun et al., 2020; Araujo et al., 2022). Nevertheless, moderate water intake restrictions (up to 33% to 40% of voluntary intake or for 24 h) seem tolerated by Nadji or Santa Inês sheep breeds without compromising their production performance. This scenario suggests the possibility of implementing watering conservation strategies during water scarcity periods or as a resource-conservation measure for desert environments without endangering meat production in some breeds (Dos Santos et al., 2019; Araujo et al., 2022). Regarding milk production, water shortage is usually associated with decreased milk yields. This reduction is because of slower mammary blood flow due to dehydration (Alamer, 2009). Reduced milk production in sheep and goats is usually accompanied by an increased in lactose, fat, and mineral salts concentration in milk (Casamassima et al., 2018), although decreased lactose concentrations have been reported in water-restricted sheep due to lactose secretion inhibition induced by cortisol (D’Ambrosio et al., 2018). As other production traits, milk production very much depends on resilience of the breed to water shortage. It has been shown that Aardi goats are very capable of withstanding water restrictions by economizing body water and striking new water balances with a 50% of water restriction, this adaptive response would allow dams to maximize lactation performance under water (and heat) stress conditions (Alamer, 2009). Conversely, lack of drinking water can significantly affect milk production levels in high production breeds that are poorly-adapted to water stress, like Lacaune dairy sheep, with tolerance to approximate water restrictions of up to 20% (Casamassima et al., 2018). Water economy entails major physiological changes in ruminants. When normal physiological limits are exceeded by water restriction, hormonal dynamics are altered to minimize water loss and to maintain osmotic balances in the internal milieu (Jaber et al., 2004). Stress can modify certain blood parameters, such as blood osmolarity, blood cell concentration, or hormone concentration. With plasma osmolality, an increase in sodium (Na+; Jaber et al., 2004; Kaliber et al., 2016) and chloride (Cl−) concentrations (Jaber et al., 2004), and a decline in potassium (K+) concentrations have been observed in sheep and goats with water restrictions, which cause blood hyperosmolality. Na+ and Cl− (the predominant cation and anion) are the primary factors that determine extracellular fluid (ECF) osmolality in blood and are implicated in acid-base metabolism. To maintain an Na+ and Cl− balance in body fluids, different small ruminant breeds increase renal retention due to the influence of aldosterone and arginine-vasopressin (Jaber et al., 2013). These two hormones are implicated in the control of the body fluid balance with water restriction, including renal excretion (Hamadeh et al., 2006; Ghanem et al., 2008), which decreases urine flow and volume (Jaber et al., 2013). Jaber et al. (2004) and Kaliber et al. (2016) report increased creatinine and urea in blood when sheep and goats were affected by water restriction, which can be partially a consequence of the re-absorption of these compounds, plus a reduced urine flow rate, and can also be due to the endogenous nitrogen source, which is related to proteolysis as a response to the protein/nitrogen intake deficiency observed when small ruminants are deprived of water. Potassium excretion through urine increases given its negative correlation with Na+, and blood K+ decreases, which are related to its intra-erythrocytic diffusion (Jaber et al., 2004) Regarding hematology variables, water stress causes hemoglobin and hematocrit increases, along with a greater total protein concentration, which are related to a smaller plasma volume (hemoconcentration). Increased total protein could result from an increase in blood albumin and globulin, which are responsible for maintaining an osmotic equilibrium between the blood and tissue fluids required when feed intake declines (Khnissi et al., 2016). Like other stressful conditions, it is assumed that water restriction can alter the immune function in small ruminants, mainly through the mediation of glucocorticoid stress hormones. Accordingly, endocrine stress markers, such as increased concentrations of cortisol or changes in differential leukocyte counts, have been reported in goats and sheep deprived of water (D’Ambrosio et al., 2018; Akinmoladun et al., 2020). However, changes in stress markers are not always associated with an impaired immunity function, and unchanged (Jaber et al., 2004; Ghanem et al., 2008) or even less concentrations of cortisol have been observed in water-restricted Awassi ewes (Hamadeh et al., 2006). Therefore, water stress effects on immunity should be assessed by examining specific immune parameters. Ghassemi Nejad et al. (2014) studied water restriction effects after feeding on the immunoglobulin G concentration in already heat-stressed Corriedale ewes to find no difference between the control and water-restricted ewes. Conversely, Barbour et al., (2005) reported that water stress in Awassi ewes reduced immune response efficacy by reducing antibodies postvaccination. The noted different patterns of humoral response suggest that the immune response of water-deprived ewes was determined by the nature of not only immunogens, but also by physiological status of the individual because immunosuppression was more significant in lactating ewes than in unproductive water-deprived ewes. Finally, D’Ambrosio et al. (2018) used haptoglobin as a marker of systemic inflammation in sheep exposed to progressive decreasing water availability. They reported that water deprivation was related to a general inflammatory condition, which indicates that water stress activates an inflammatory pathway that includes haptoglobin, platelet factor 4 (PF4 cytokine), and ApoA-II lipoprotein with anti-oxidant and anti-inflammatory activity. The authors suggested that these markers might be combined to identify dehydrated animals and to monitor homeostasis restoral. Apart from the physiology response to water stress conditions, some feeding strategies are adopted to mitigate water stress. One of the main effects of water restriction is reduced feed intake because water and feed intake are closely related. Therefore, diet should be of high quality to ensure the greatest possible nutrient intake. Van Der Walt et al. (1999) reported a similar intake in Mutton Merino wethers fed with low or medium protein diet with 50% water restriction. The wethers fed with medium protein presented slightly greater gains. Similarly, desert goats subjected to 40% water restriction lost more BW with low-quality hay than the goats fed with good-quality hay, and no differences in dry matter intake were reported (Ahmed and El Kheir, 2004). These studies highlight that a high-quality diet can help to alleviate water stress. In addition, it is known that some supplements can also help to cushion the water stress impact. Although one of the most studied supplements is vitamin C, its supplementation is not a common practice in ruminants because they can biosynthesize under normal conditions. The interest in vitamin C supplementation is for its decrease in animals under stressful conditions (Akinmoladun et al., 2020) and its anti-oxidant capacity (free radical scavenging), which can improve the immune response (Chedid et al., 2014). For this reason, vitamin C administration has been studied in different stressed animals (i.e., pigs, broilers, goats, sheep, rabbits) with positive results (Chedid et al., 2014). In line with this, Awassi ewes supplemented with 2.5 g vitamin C/d under severe water restriction conditions presented with less BW loss and showed less marked increases in serum protein, globulin, and albumin concentrations compared with un-supplemented ewes, and without affecting FFA, cholesterol, glucose, serum cortisol and K+ (Ghanen et al., 2008.) Similarly, Jaber et al. (2011) studied vitamin C supplementation at different doses (3 g or 5 g daily, or two large doses of 10 g (8 d apart)) in Awassi ewes with a 3-d water restriction. They reported less BW loss compared with their counterparts without vitamin C, and no effect on fat mobilization was observed. Recently, Akinmoladun et al. (2020) that vitamin C supplementation in goats indigenous under water stress and high temperature conditions on loss dry matter intake and blood Although vitamin C supplementation be a to mitigate the effect of water stress on small ruminants by especially reducing loss it is important to note that vitamin C was in the above-mentioned which could flock management difficult or especially in extensive systems without water. Therefore, it is to continue for different supplements to mitigate water stress effects and some that are to in different In strategies from vitamin C supplementation to alleviate water stress have been studied in ruminants. In heat stress and the to mitigate its effects have been extensively especially in dairy One to mitigate heat stress is dietary to immune function and status. these and vitamin supplementation in heat-stressed sheep effects et al., with a of inflammatory and an of species et al., 2014). As water deprivation was related to a general inflammatory condition, and this can be to mitigate the effects of this stress. studied was to increase fat in the diet with in and because fat is related to decreased metabolic In addition, the of fatty acids in diet has been studied in recent and enhanced immune function in heat stress has been reported in sheep et al., the for is especially with a to for the strategies that mitigate water stress effects on small ruminants. It would be to the of different and in diet to help ewes to balance the negative effect of water stress. The control of this has been and very studies have been to determine ruminants are in water. One of the studies to measure in water use of ruminants was by et al. in In that the water intake, water intake and water to were as were related to feed intake, feed intake and dry matter intake, as as traits like average daily water intake can be a water use and, to feed intake, it indicates the difference between the observed water intake of the animal and water These authors moderate for these traits to between water and water intake and water to which indicates that their can be The low between water intake and average daily were also but the with dry matter intake were moderate and positive and water intake with feed intake in cattle similar results for these to find positive for water intake with dry matter intake et al., 2022). In small ruminants, only one by et al. has water intake and water intake in to these traits with These authors that water intake with dry matter intake in to BW and the feed rate but with the water to In the more animals in water use high dry matter intake in to BW and better feed These water use results suggest the possibility of these traits in ruminant However, more studies with these traits in small ruminants should be in animal have to that the of the water intake on individual animals for traits like average daily gain, or dry matter intake. This also animals in individual pens or systems that allow individual to be Additionally, water use of the animal from tolerant animals to water stress. 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(2016) in sheep was in one significant of a This protein is in the of renal and a critical in the and water re-absorption Finally, a in breeds showed of to be associated with environmental et al., 2018). were based for temperature and and indicate water but without from other Breeding strategies are difficult to in extensive systems given the need to animals to of the in meat small ruminants. in dairy or meat intensive small ruminant production, water use can be a including because of its moderate is technologies to water shortage of the animal tolerance especially in and This is it is to with an of for the water stress to identify the that water shortage and to acquire the mechanisms response to these traits. 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