Heat Stress In Sheep Research Articles

Influence of Management Systems on Severity of Heat Stress and Reproductive Performance of Rams in the Tropics – A Review

Abstract Sheep are an important source of protein for humans, and recent decades have seen a significant increase in the production of sheep-based products, thus indicating an increase in demand for this commodity. At a time when this sector is growing, sheep are exposed to various challenges. These include climate change, which can cause heat stress in sheep, including rams, which later negatively affects their growth and reproductive performance. Exposure to heat stress results in physiological and reproductive behaviour responses in rams, which could also be used to visually identify the effect of heat stress as it will affect the productivity of livestock. In addition, the year-round hot and humid climate of the tropics is expected to contribute to a higher probability of heat stress occurrences in rams reared in developing countries around the equator. Nevertheless, the adaptability of rams to heat stress varies according to their origin, whereby native breeds tend to adapt better. Despite that, native breeds still can be affected by adverse environmental conditions and rely on thermoregulation mechanisms to mitigate heat stress. This results in numerous negative physiological changes, such as sweating and increased heart rate. This review highlights the effects of heat stress on the physiology, reproductive behaviour and reproductive performance of male sheep. The review also discusses the impact of management systems on heat stress in rams, which affects sheep productivity.

Feed additives supplementation: a potential strategy to ameliorate heat stress in sheep

Abstract Given a significant climate-flexible and socio-economic role in developing nations, environmental heat stress imposes a major financial impact on sheep production systems globally endangering their production, reproduction, and growth. In this regard, the adverse effects of heat stress on sheep production systems have to be addressed through adoption of effective heat alleviation measures like animal management, nutritional management and genetic interventions of which the nutritional interventions seems to be the most cost effective way to alleviate heat stress. Nutritional manipulation for heat stress alleviation in sheep involves the use of antioxidant supplements (Vitamin B; Vitamin E and Selenium; Selenium; Zinc sulphate and folic acid; Vitamin C, Vitamin E, Selenium and Zinc; Naringin; Opuntia ficus-indica f. inermis; Açai oil and Brown seaweed like Ascophyllum nodosum and Sargassum latifolium). Further, electrolyte supplements (Dietary Electrolyte Balance (DEB); Sodium bicarbonate and potassium bicarbonate; Sodium hydroxide) have a beneficial effect on thermal responses, respiratory activities, gas exchange parameters, rumen fermentation, blood buffering capacity and acid-base balance. The mineral mixture supplements (Mineral blocks; Mineral mixture and antioxidants; Chromium; Zinc) play a crucial role in increasing the efficiency of antioxidant defence system, immunity-related parameters, production, reproduction, feed digestibility and insulin sensitivity. Probiotic supplements (Lactobacillus acidophilus, Saccharomyces cervisiae, Propionibacterium freudenreichii, Lactobacillus casei, Enterococcus faecium, Lactobacillus lactis, Bacillus subtilis, Propionibacterium freudenreichii, Pediococcus cerevisiae, Megaspha eraelsdenii, Bacillus licheniformis, Aspergillus oryzae, Schizochytrium limacinum, Trichoderma reesei and Saccharomyces cerevisiae) improve lactational performance, dietary energy utilization and productivity. The probiotics (live Saccharomyces cerevisiae) and prebiotics (mannan oligosaccharide plus b-glucans) used in heat stress alleviation improve dietary energy utilisation. Furthermore, the vital role of herbal supplements (Rosemary, Cinnamon, Turmeric, Clove, Naringin, Chestnut tannins, Giloy stem powder, Curcumin, Rocket oil (watercress oil), Flaxseed, Cornus, Oregano, Thyme, Chamomile flowers, Moringa oleifera, Betaine) has been highlighted to promote feed intake, antioxidant status, growth performance, feed utilization, reproductive performance and immune response. Effective adoption of nutritional strategies can thus ensure sustainable sheep production in this changing climate scenario.

Molecular Mechanism of m6A Methylation Modification Genes METTL3 and FTO in Regulating Heat Stress in Sheep.

Heat stress is an important environmental factor affecting livestock production worldwide. Primary hepatocytes and preadipocytes derived from Hu sheep were used to establish a heat stress model. Quantitative reverse transcriptase-PCR (qRT-PCR) analysis showed that heat induction significantly increased the expression levels of heat stress protein (HSP) genes and the N6-methyladenosine (m6A) methylation modification genes: methyltransferase-like protein 3 (METTL3), methyltransferase-like protein 14 (METTL14), and fat mass and obesity associated protein (FTO). Heat stress simultaneously promoted cell apoptosis. Transcriptome sequencing identified 3980 upregulated genes and 2420 downregulated genes related to heat stress. A pathway enrichment analysis of these genes revealed significant enrichment in fatty acid biosynthesis, degradation, and the PI3K-Akt and peroxisome proliferator-activated receptor (PPAR) signaling pathways. Overexpression of METTL3 in primary hepatocytes led to significant downregulation of HSP60, HSP70, and HSP110, and significantly increased mRNA m6A methylation; FTO interference generated the opposite results. Primary adipocytes showed similar results. Transcriptome analysis of cells under METTL3 (or FTO) inference and overexpression revealed differentially expressed genes enriched in the mitogen-activated protein kinase (MAPK) signaling pathways, as well as the PI3K-Akt and Ras signaling pathways. We speculate that METTL3 may increase the level of m6A methylation to inhibit fat deposition and/or inhibit the expression of HSP genes to enhance the body's resistance to heat stress, while the FTO gene generated the opposite molecular mechanism. This study provides a scientific basis and theoretical support for sheep feeding and management practices during heat stress.

Reducing the Fermentability of Wheat with a Starch Binding Agent Reduces Some of the Negative Effects of Heat Stress in Sheep.

Simple SummaryHeat stress is one of the major problems affecting the thermotolerance of livestock in Australia and in many parts of the world. Dietary interventions are considered to be one of the effective strategies to beat the heat. Hence, this study evaluated the benefits of reducing the fermentability of wheat grains (BioprotectTM) in the diet of Merino lambs. These results indicated that Bioprotect supplementation had a positive effect on the respiratory rate and heart rate of heat-stressed lambs.The objective of this study was to investigate the effects of reducing the fermentability of grains on thermoregulatory responses in heat stressed (HS) lambs. To achieve this, wheat grain treated with a commercial starch binding agent, Bioprotect, is compared to maize, which has already demonstrated effects in ameliorating heat stress-induced thermoregulation responses and untreated wheat grains. An initial in vitro experiment was conducted to examine cumulative gas production from the fermentation of wheat grain with different dosages of the commercial starch binding agent, Bioprotect. Based on the in vitro results, an in vivo lamb experiment was conducted using 24 Merino lambs (1 year old; 42.6 ± 3.6 kg BW). The lambs were offered one of three dietary treatments: a wheat-based diet (WD), a Bioprotect treated wheat-based diet (BD), and a maize-based diet (MD). Three successive 1-week experimental periods were conducted with lambs from all dietary groups (P1, P2, and P3). During P1, lambs were exposed to a TN environment and fed a 1.7× Maintenance feed intake (MF) level; in P2, lambs were kept in a HS environment and fed a 1.7× MF level; and in P3, animals were kept in a HS environment and fed a 2× MF level. The in vitro experiment revealed a reduction in cumulative gas production (p < 0.05) from the Bioprotect treated wheat compared to untreated wheat samples. In the in vivo component of the study, the replacement of wheat with maize or 2% Bioprotect-treated wheat reduced the respiration rate (p < 0.001) and heart rate (p ≤ 0.01) of lambs during HS. There was a reduction in the concentration of blood gas variables such as a base excess of blood (BE(b)) and extracellular fluid (BE(ecf)), bicarbonate (CHCO3−), the partial pressure of carbon dioxide (pCO2), the total concentration of carbon dioxide (ctCO2), and sodium (Na+) (p ≤ 0.001 for all) during the periods of HS compared to the thermoneutral conditions. Moreover, BD- and MD-fed lambs had a higher blood potassium concentration (K+) than the WD-fed lambs (p = 0.008). The results of the present study suggest that Bioprotect can be a viable feed treatment strategy for treating rapidly fermentable grains such as wheat to alleviate the effects of HS. Further, Bioprotect-treated wheat could be an option to replace maize in concentrate rations in jurisdictions where maize is cost-prohibitive or unavailable.

Non-invasive measure of heat stress in sheep using machine learning techniques and infrared thermography

Heat stress (HS) leads to altered sheep behavior, physiological, and biochemical processes which negatively affects their welfare and performance. While suitable strategies are needed to ameliorate the impacts of HS in sheep, it is equally important to accurately and non-invasively measure HS. Traditionally, rectal temperature (RT) is considered an indicator of thermal balance and is used to assess the impacts of hot conditions on sheep. However, measuring RT itself can be a stressor as it often requires restraining of the animals. The main objective of this study was to establish whether a combination of infrared thermography (IRT) and machine learning techniques can be applied to predict sheep RT when subjected to HS. Thermal images and RT were taken twice weekly from Dorper, and 2nd Cross (Poll Dorset X (Border Leicester X Merino)) lambs (n = 24/breed, 4−5 months old), for two weeks. Sheep were randomly allocated to either (i) thermoneutral (TN; 18–21 °C, 30–50 % relative humidity (RH), n = 12/group) or (ii) cyclic HS treatments (28–40 °C, 40–60 % RH, the cycle comprised of high temperatures 38−40 °C between 0800 and 1700 h daily and 28 °C, 30–40 % RH maintained overnight). The head was selected as the region of interest because of less wool cover; specifically, the IRT of forehead, eye, ear, nostril, and face locations were measured. Artificial neural network (ANN) models were developed using three different backpropagation algorithms with temperature-humidity index (THI), and IRT temperatures as inputs and RT measured manually as targets. Results showed that the forehead and eye IRT temperatures had the highest correlation (P < 0.01) with THI and RT. Further, Bayesian Regularization, with one hidden layer containing 10 neurons with a tangent sigmoid transfer function, showed the best correlation (R = 0.92) and highest performance (MSE = 0.02). The model developed may be a rapid and cost-effective technique to monitor real-time body temperatures in sheep and also to detect HS with minimal restraint.

292 Reducing the Fermentability of Wheat with a Starch Binding Agent Has the Potential to Ameliorate Heat Stress in Sheep

Abstract Two experiments were conducted to determine whether a starch binding agent could (1) reduce the rate of fermentation of wheat grain and (2) improve heat tolerance in sheep. Firstly, fermentation kinetics and buffered rumen fluid pH variation were measured during in vitro incubation of wheat with 0, 1, 2, and 4% Bioprotect® (Feedworks Pty Ltd, Australia). Bioprotect® reduced gas production at 12 h in a dose-dependent manner (-6.4, -11 and -20% respectively; P &amp;lt; 0.001) and increased pH (P &amp;lt; 0.001), indicating slower ruminal fermentation. In a randomized control experiment, Merino lambs (n = 24) were fed either 50% wheat (WD, fast fermenting), corn (CD, slow fermenting), or wheat treated with 2% Bioprotect® (BD), with the balance of the diets being forage. Lambs were housed in climate-controlled rooms and exposed to 3 experimental periods: period 1 (P1: 7 days of thermoneutral conditions [18–21°C and 40–50% relative humidity (RH)] and fed 1.7×maintenance); period 2 [P2: 7 days of HS (28–40°C and 30–50% RH) and fed 1.7×maintenance]; and period 3 (P3: 7 days of HS as in P2, and 2×maintenance) with ad libitum water. Increases in respiration rate (RR), heart rate (HR), rectal temperature (RT) and left and right flank skin temperature (P &amp;lt; 0.001) occurred during HS, particularly during P3 (P &amp;lt; 0.001). Lambs fed CD and BD had lower RR (150, 137 and 140 breaths/min for WD, CD and BD, P &amp;lt; 0.001), HR (91.3, 85.3 and 85.9 beats/min, P &amp;lt; 0.001 and RT (39.7, 39.7 and 39.7°C P &amp;lt; 0.05). While there was no effect of diet, lambs reduced feed intake (-4%, P &amp;lt; 0.05) during P2 but consumed more (+16%) during P3. These data confirm that feeding corn or Bioprotect® treated wheat can be used as an ameliorative strategy to reduce the thermal load in lambs during summer.

275 Access to Shade Mitigate Heat Stress and Improves Growth Performance in Lambs During Summer

Abstract The objective of the present study was to investigate the effects of provision of shade on behavior, physiology, and growth of Merino lambs exposed to natural Australian summer conditions. Sixty Merino lambs were randomly allocated to either pasture with shade (n = 30;paddock with trees) or a pasture without shade (n = 30;paddock without any trees) for one month during southern-Australian summer (February-2021). Sheep were grazing on the pastures as per standard protocols followed on the farm with ad libitum access to water. Lambs were monitored twice daily between 0900-1000h and 1400-1600h to record their behavior, and physiological parameters were recorded on hot days (environmental temperature (T) &amp;gt;30°C). Behavioral patterns were represented as the proportion of animals doing specific activities in each treatment group. Grazing was the most frequent activity observed in animals during morning measurement (&amp;gt; 60% in both groups). However, high temperature (T &amp;gt; 30°C) decreased grazing behavior in sheep to &amp;lt; 5% in both treatments. Standing behavior was significantly greater (65.2 vs 21.6%; P &amp;lt; 0.05) for animals under non-shade treatment, while lying behavior was more frequent (17.3 vs 76.3%; P &amp;lt; 0.01) in animals having access to shade. Significantly more animals were seeking water troughs (P &amp;lt; 0.05) in the non-shade group (33.2%) compared to the shade group (10.3%). On an average hot day (T &amp;gt;28°C), most lambs in the shade group were seeking shade (P &amp;lt; 0.01), and when the temperature exceeded &amp;gt;32°C, 90% of the lambs were seeking tree shade. Sheep with access to shade exhibited lower (P &amp;lt; 0.01) respiration rate (117breaths/min) and rectal temperature (39.7°C) than non-shade group (151breaths/min;40.2°C). Overall, access to shade improved (P &amp;lt; 0.001) average daily gain (+0.047kg/day) in sheep compared to the non-shade group (-0.028kg/day). In conclusion, our research confirms that providing access to shade is an effective ameliorative strategy to mitigate heat-stress in sheep during summer heatwaves.

Impacts of seasonal ambient temperature and humidity on meat quality characteristics of sheep and beef longissimus thoracis muscles

The effects of seasonal temperature and humidity on meat quality characteristics of sheep (12 months of age) and beef cattle (24 months of age) were investigated. Samples of longissimus thoracis (500 g) muscle were randomly collected from 96 sheep and 48 beef cattle between November 2018 and October 2019. All the meat samples were kept in the chiller at 4-5ºC for 48 h. The samples were collected over a 12-month period and this period was divided into two seasons based on ambient temperature and relative humidity in Basrah region. Theses seasons were named: Cool Season (November to March with average temperature of 23.0±1.54ºC and 59.0±1.75% relative humidity) and Hot Season (April to October with average temperature of 40.5±1.77ºC and 53.5±5.98 relative humidity). The ultimate pH (pHu), expressed juice, cooking losses, shear force, sarcomere length, myofibrillar fragmentation index and colour lightness (L*), redness (a*), and yellowness (b*) parameters were determined. The effect of the season on meat quality characteristics of the Longissimus thoracis muscle from both species was found to be significant (P&lt;0.05). The hot season muscle samples had significantly (P&lt;0.05) higher pHu values, longer sarcomere length, higher myofibrillar fragmentation index with significantly (P&lt;0.05) lower shear force values than the muscle samples collected during the cool season. Sheep and beef longissimus thoracis muscles from the hot season group had significantly (P&lt;0.05) darker meat than that those of the cold season group, based on L*, a* and b* colour measurements. The present findings indicated that hot temperature (&gt;40ºC) leads to heat stress in sheep and cattle, which increased the muscle pHu and influenced other related meat properties. These findings will assist meat producers to improve meat quality parameters by slaughtering livestock at early hours of the day. Hot temperature has also an impact on animal welfare.

Panting scores as a measure of heat stress evaluation in sheep with access and with no access to shade

The threat to sheep welfare of heat stress when pastured outdoors in the summer, particularly without access to shade, has been underinvestigated. This may be of importance not only in hot climates, but also during the summer months in cooler climates. This study considered whether, in the moderately warm conditions of a northern European summer, sheep will access shade of they have access to it, and if sheep with no access to shade in a northern European summer show behaviours indicative of poor welfare, including measures of panting scores and other indicators of heat stress. There were twelve sheep in each of the groups, the control group (NS) or the treatment group with the possibility to access shade (SH). Respiration rates and panting scores were recorded for each sheep in each group twice each day. Other behaviours were also recorded at the individual animal level. In the SH group, the numbers of sheep in the shaded areas were also noted. Climatic data on observation days was collected. Respiration rates were significantly higher at higher panting scores (p < 0.001). Higher panting scores were recorded for NS sheep than for SH sheep (p < 0.001), as were breath intensities (p < 0.001). The behaviour of open mouth with tongue extended was not observed in the SH group but was observed in the NS group. SH sheep ruminated more (p = 0.011) than the NS sheep, while NS sheep stood panting more than the SH sheep (p = 0.001). Indicators of heat stress, respiration rates and panting scores, were more strongly correlated to air temperature and weather conditions in the NS group compared to the SH group, and these were significant. The number of animals observed to be in the shade in the SH group was positively correlated with air temperature. Panting score can therefore be used as a reliable measure for estimating respiration rate and heat stress in sheep. Sheep, even in northern Europe, can suffer from heat stress, particularly when given no access to shade, and shade from the sun should be provided for sheep at pasture.

M6A mRNA methylation analysis provides novel insights into heat stress responses in the liver tissue of sheep

N6-methyladenosine (m6A) mRNA methylation varies in response to stress. However, no map of m6A mRNA methylation has been obtained for sheep, nor is it known what effect this has on regulating heat stress in sheep. Here, we obtained m6A methylation maps of sheep liver tissues with and without heat stress by MeRIP-seq. In total, 8306 m6A peaks associated with 2697 genes were detected in the heat stress group, and 12,958 m6A peaks associated with 5494 genes were detected in the control group. Peaks were mainly enriched in coding regions and near stop codons with classical RRACH motifs. Methylation levels of heat stress and control sheep were higher near stop codons, although methylation was significantly lower in heat stress sheep. GO and KEGG revealed that differential m6A-containing genes were significantly enriched in the stress response and fat metabolism. Our results showed that m6A mRNA methylation modifications regulate heat stress in sheep.

Discovery and validation of candidate SNP markers associated to heat stress response in pregnant ewes managed inside a climate-controlled chamber.

Sheep production in desert environments during summer is challenging due to heat stress which reduces feed intake, growth, and fertility. Despite warm conditions, some ewes are able to maintain a normal performance suggesting the existence of genetic bases underlying heat tolerance. Our objective was to discover and validate genetic markers associated with thermo-tolerance in pregnant ewes exposed to warm environmental conditions. Using a well-defined model laboratory of heat stress in sheep, pregnant Columbia-Rambouillet crossbred ewes (n = 100) were examined. Following acclimation to the laboratory at thermo-neutral conditions, heat stress was induced in ewes by increasing the temperature-humidity index in a control environmental chamber during mid-gestation. Feed intake, water consumption, and rectal temperature were recorded daily and used to establish the heat stress tolerance index (HSTI) for each ewe. Rectal temperature was a predictor (P < 0.05) of feed intake, and the regression coefficient was used to classify the HSTI. In a subset of 24 ewes, a genome-wide association study (GWAS) was performed using the Illumina OvineSNP50 BeadChip. Single-marker analysis detected 3 intragenic SNPs associated with HSTI (P value = 10-5). Bayesian multi-marker approach discovered 26 chromosomal regions across the genome which accounted for 9.8% of the variation associated with HSTI. In an independent sheep population (n = 42), the three discovered SNPs were validated as molecular markers associated with thermo-tolerance phenotypic traits. These SNPs were located within the genes F13A1, PAM, and PRELID2. In conclusion, three SNPs appear to be novel molecular markers associated with heat stress tolerance in pregnant ewes providing new knowledge about genetic foundations of thermo-tolerance.

Transcriptome analysis reveals corresponding genes and key pathways involved in heat stress in Hu sheep.

Heat stress (HS) seriously affects animal performance. In view of global warming, it is essential to understand the regulatory mechanisms by which animals adapt to heat stress. In this study, our aim was to explore the genes and pathways involved in heat stress in sheep. To this end, we used transcriptome analysis to understand the molecular responses to heat stress and thereby identify means to protect sheep from heat shock. To obtain an overview of the effects of heat stress on sheep, we used the hypothalamus for transcriptome sequencing and identified differentially expressed genes (DEGs; false discovery rate (FDR) < 0.01; fold change > 2) during heat stress. A total of 1423 DEGs (1122 upregulated and 301 downregulated) were identified and classified into Gene Ontology (GO) categories and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Heat stress triggered dramatic and complex alterations in gene expression in the hypothalamus. We hypothesized that heat stress induced apoptosis and dysfunction in cells and vital organs and affected growth, development, reproduction, and circadian entrainment via the calcium signaling pathway, which influences ribosome assembly and function. Real-time PCR was used to evaluate the expression of the genes regulating important biological functions or whose expression profiles were significantly changed after acute heat stress (FDR < 0.01; fold change > 4), and the results showed that the expression patterns of these genes were consistent with the results of transcriptome sequencing, indicating that the credibility of the sequencing results. Our data indicated that heat stress induced calcium dyshomeostasis, blocked biogenesis, caused ROS accumulation, impaired the antioxidant system and innate defense, and induced apoptosis through the P53 signaling pathway activated by PEG3, decreased growth and development, and enhanced organ damage. These data is very important and helpful to elucidate the molecular mechanism of heat stress and finally to find ways to deal with heat stress damage in sheep.

The role of N6-methyladenosine RNA methylation in the heat stress response of sheep (Ovis aries).

With the intensive development of the sheep industry and increasing global temperatures, heat stress in sheep has become an increasingly severe and important issue in recent years. The level of N6-methyladenosine (m6A) RNA methylation changes in response to stress plays important roles in stress responses. However, the role of m6A in the heat stress response of sheep remains unclear. To explore this issue, we measured heat stress protein (HSP) expression, liver function indexes, m6A on RNA, m6A-related enzyme expression, and tissue damage in sheep that had been subjected to heat stress. At the transcriptome level, our results showed significant increases in m6A on RNA and increased mRNA levels of HSPs (HSP70, HSP90, and HSP110) and m6A-related enzymes [METTL3 (methyltransferase-like 3), METTL14 (methyltransferase-like 14), WTAP (wilms tumor 1-associated protein), FTO (fat mass and obesity-associated protein), ALKBH5 (alkB homologue 5), YTHDF1-3 (YTH domain family proteins), and YTHDC1-2 (YTH domain-containing proteins)] following heat stress. At the protein level, the expression of METTL3, YTHDF1-2, and YTHDC2 showed no significant differences following heat stress. However, in contrast to its mRNA level after heat stress, the protein expression of YTHDF3 was reduced, while the expression of HSPs (HSP70, HSP90, and HSP110), METTL14, WTAP, FTO, ALKBH5, YTHDF3, and YTHDC1 increased in line with their measured mRNA levels. Histological experiments revealed that heat stress caused varying degrees of damage to sheep liver tissue. Moreover, immunohistochemical staining indicated that the m6A-related enzymes were expressed in sheep hepatocytes, and differences in expression patterns were observed between the control and heat stress groups. In summary, differences in the level of m6A and the expression of m6A-related enzymes in the liver of sheep were observed after heat stress. This indicates that m6A is involved in the regulation of heat stress in sheep. Our findings provide a new avenue for studying the responses to heat stress in sheep.

The occurrence of ryegrass staggers and heat stress in sheep grazing ryegrass-endophyte associations with diverse alkaloid profiles

AIMS: To compare ryegrass pastures infected with endophytes producing diverse alkaloids for their ability to cause ryegrass staggers in grazing lambs; to compare respiration rates and rectal temperatures of these lambs after exposure to heat stress, and to compare liveweight gains during the study period.METHODS: Ryegrass pastures of cultivar Trojan infected with NEA endophytes, branded NEA2 (T-NEA2), endophyte-free Trojan (T-NIL), Samson infected with standard endophyte (S-STD), Samson infected with AR37 endophyte (S-AR37) and endophyte-free Samson (S-NIL), were grazed by lambs (n=30 per cultivar) for up to 48 days in February and March of 2012 and 2013. Pasture samples were analysed for alkaloid concentrations and lambs were scored for ryegrass staggers at intervals during the study period. Liveweight was recorded at the start (Day 0) and end of the study, and rectal temperatures and respiratory rates were measured in lambs exposed to heat stress on Days 23 and 26, in 2012 and 2013, respectively.RESULTS: Concentrations of alkaloids were lower in 2012 than 2013, associated with warmer and drier conditions in 2013, and the prevalence of ryegrass staggers was low in 2012. In 2013, concentrations of ergovaline were similar in T-NEA2 and S-STD, but concentrations of lolitrem B were lower in T-NEA2 than S-STD. S-AR37 produced epoxy-janthitrems but no lolitrem B or ergovaline. In 2013, by Day 20, 9/30 (30%) sheep grazing S-STD had severe staggers (score ≥4), and by Day 47 all sheep had been removed from this cultivar due to severe staggers. By Day 47, 18/30 (60%), 4/30 (13%) and 0/30 (0%) sheep grazing S-AR37, T-NEA2 and T-NIL pastures, respectively, had severe staggers. There were no differences in mean daily weight gain of lambs between cultivars in either year. In both years, mean rectal temperature and respiration rate following exposure to heat stress were highest in sheep grazing S-STD and T-NEA2, and lowest in sheep grazing T-NIL.CONCLUSIONS: In lambs grazing different ryegrass pastures infected with endophytes, ryegrass staggers was most severe on S-STD, less severe on S-AR37 and least on T-NEA2. When under heat stress, lambs grazing ergovaline-producing S-STD and T-NEA2 pastures had increased respiration rates and rectal temperatures compared with lambs grazing T-NIL.CLINICAL RELEVANCE: If ambient temperatures are suitable, NEA2-branded endophytes have the potential to express concentrations of ergovaline sufficient to induce heat stress in grazing sheep.

Towards Heat Stress Management in Small Ruminants – A Review

Abstract Small ruminants (sheep and goats) play a predominant role in the economy of million people, and have provided meat, milk, skin, wool and fiber for centuries. Animals undergo various kinds of stressors, i.e. physical, nutritional, chemical, psychological and heat stress (HS). Among all, HS is the most concerning at present in the ever-changing climatic scenario. Climate change is the most serious long-term challenge faced by small ruminants’ owners worldwide. HS results in decreased growth, reproduction, production, milk quantity and quality, as well as natural immunity, making animals more vulnerable to diseases, and even death. Thus, HS results in great economic losses, emphasizing the necessity to objectively assess animal welfare. The increasing demand for animal products paralleled by the frequent hot climate is a serious threat for the agriculture sector. The ability of sheep and goats to cope with HS without harming their welfare and productive performance has been often overrated. To date, little attention has been paid to comprehensive detailed data on the adverse effect of HS on sheep and goats. Therefore, this review discusses in detail the sheep and goats’ behavioral, physiological, molecular/cellular, hematological, biochemical and immunological responses under HS conditions. In addition, this review also presents the adverse effects of HS on reproduction and fertility, milk quantity and quality, feed intake, and water consumption of sheep and goats. Finally, this review suggests various methods for HS alleviation. In conclusion, HS impairs productivity and well-being in sheep and goats. The improved understanding of the impact of HS on small ruminants will help in developing management techniques to alleviate HS and highlighting the need for future researches on HS in sheep and goats.

Estresse Térmico e sua Influência na Fisiologia Hormonal de Pequenos Ruminantes

Over the years with changes in both production and marketing aspects of the operation of goats and sheep has been highlighted and is widespread throughout the world. The sheep and goat production systems are affected by several restrictive elements that can compromise their development, among which stands out the adverse weather conditions that contribute to the reduction of the herd productivity. In conditions of thermal stress, the animals begin a series of mechanisms regulated by hormones and coordinated by the nervous system and the endocrine system. In this context, the objective was to make a literature review on hormone physiology in control of heat stress in sheep and goats. Hormonal changes detected in animals under heat stress affects both their productive performance as the reproductive, predisposing the onset of diseases, stunted growth or reproductive harm. Changes in behavior are the first visible signs triggered by hormonal changes due to thermal stress.

High dietary selenium and vitamin E supplementation ameliorates the impacts of heat load on oxidative status and acid-base balance in sheep1,2

The objective of this study was to determine the efficacy of supranutritional dietary selenium and vitamin E (Vit E) to ameliorate the effect of heat stress (HS) on oxidative status and acid-base balance in sheep. Thirty-two Merino × Poll Dorset ewes were acclimated to indoor individual pen feeding of a pelleted control diet (0.24 g Se and 10 IU of Vit E/kg DM) for 1 wk. Sheep were then moved to metabolism cages in climatic chambers and randomly allocated to a 2 × 2 × 2 factorial design with the respective factors being dietary Se (0.24 and 1.20 mg/kg DM as Sel-Plex; Alltech, Australia), Vit E (10 and 100 IU/kg DM), and temperature for 2 wk. After 1 wk of acclimation in metabolic cages, 1 climatic chamber continued on thermoneutral (TN) conditions (18°C to 21°C and 40% to 50% relative humidity [RH]), and the other one was set to HS conditions (28°C to 40°C and 30% to 40% RH) for 1 wk. The sheep were then returned to individual pens and fed the control diet for 1 wk before being returned to the same diet as in the first period but a reversed thermal treatment for a further 2 wk. Physiological parameters were recorded 3 times daily, and blood samples were collected on d 1 and 7 of thermal treatment. Average respiration rate and rectal temperature of sheep were increased (P < 0.001) during HS; however, combined supranutritional supplementation of Se and Vit E reversed the effects of HS. Sheep given the high Se and high Vit E diet had a lower respiration rate (191 vs. 232 breaths/min; P = 0.012) and rectal temperature (40.33°C vs. 40.58°C; P = 0.039) under peak HS (1700 h) compared with those fed the low Se and low Vit E diet. Plasma reactive oxygen metabolites concentrations were reduced (P = 0.048) by 20%, whereas biological antioxidant potential was increased (P = 0.17) by 10% in sheep fed the high Se and high Vit E diet compared with those fed the low Se and low Vit E diet. Blood pH was elevated (P = 0.007) and bicarbonate was reduced (P = 0.049) under HS, and again, these effects were ameliorated by the high Se and high Vit E diet. Both white blood cell glutathione peroxidase gene expression and red blood cell lysate glutathione peroxidase activity were increased in sheep fed the high Se and high Vit E diet. These data suggest that supranutritional dietary Se or Vit E can reduce some of the negative effects of HS. However, the synergism between the 2 antioxidants improves their potential to ameliorate the impacts of HS in sheep.

Exhaled breath condensate hydrogen peroxide concentration, a novel biomarker for assessment of oxidative stress in sheep during heat stress

The present study aimed to measure hydrogen peroxide (H2O2) in exhaled breath condensate (EBC) as an index of oxidative stress induced by heat stress (HS) and to evaluate the antioxidant potential of supranutritional levels of selenium (Se) and vitamin E under HS conditions in sheep. Thirty-two Merino × Poll Dorset ewes (in two replicates) were acclimated to indoor individual pen feeding of a pelleted control diet (0.24 g Se and 10 IU of vitamin E/kg DM) for 1 week. Sheep were then randomly allocated to a 2 × 2 factorial design with the respective factors being dietary Se (0.24 and 1.20 mg/kg DM as Sel-Plex) and vitamin E (10 and 100 IU/kg DM) for 2 weeks. After 1 week acclimation to the diets the sheep were placed in metabolism cages in one of two climatic chambers set to either thermoneutral (18−21°C and 40–50% relative humidity) or HS (28−40°C and 30–40% relative humidity) conditions for 1 week. Average respiration rate and rectal temperature were increased (P &lt; 0.001) during HS. Similarly, H2O2 concentration in EBC and plasma reactive oxygen metabolites were increased significantly (P = 0.041 and P = 0.002, respectively), in sheep exposed to HS. The EBC H2O2 concentration was reduced (P &lt; 0.05) in sheep fed the diet supplemented with supranutritional levels of both Se and vitamin E. Sheep supplemented with antioxidants also had lower respiration rates (191 vs 232 breaths/min, P = 0.012) and rectal temperature (40.33 vs 40.58°C, P = 0.039) under peak HS (1300 hours and 1700 hours) compared with those on the control diet indicating an improved capacity to handle HS. These data suggest that the H2O2 concentration in EBC can be utilised as a novel biomarker to demonstrate oxidative stress induced by HS in sheep.

AMELIORATIVE EFFECT OF ASCORBIC ACID ADMINISTRATION AND CHILLED DRINKING WATER ON RAM LAMBS EXPOSED TO HEAT STRESS DURING SUMMER SEASON.

ABSTRACTThe ameliorative effect of ascorbic acid supplementation and drinking chilled water on heat stress was studied on ram lambs. Twenty male ram lambs were randomly divided into four equal groups of five animals each and nearly similar in age and weight. The 1st group served as control (CTR), the 2nd group was given cold water (10-15 °C) without adding vitamin C (G1), the 3rd group was supplemented with ascorbic acid at rate 2.5 g/h/d (G2), the 4th group was supplemented with ascorbic acid in addition to the cold water (G3). All animals exposed to the same managerial and climatic condition during the complete experimental period. Body weight (BW) recorded at the beginning, then at biweekly intervals until end of the experiment. Feed intake, feed conversion efficiency, water intake per unit body gain and water intake per unit feed intake were calculated for each lamb. Rectal and ear temperatures, respiratory and pulse rates were measured. Blood plasma samples were analyzed for some blood constituents (total protein, albumin, globulin, glucose, total cholesterol, ALT, AST, calcium (Ca++) and potassium (K+)). Total protein, albumin, globulin, glucose, cholesterol and calcium concentrations were significantly higher (P≤0.001), however liver enzymes AST and ALT were significantly lower (P≤0.001) in the blood plasma of treated lambs (G1, G2 and G3) than those in control group. Cumulative feed intake, body weight gain, and cumulative water intake were significantly higher (P≤0.01) in G3 than other three groups. Rectal temperature (P≤0.05), respiration rate and pulse rate (P≤0.01) increased significantly, while ear temperature was not significantly affected by treatment. In conclusion, ascorbic acid supplementation ameliorates the adverse effect of heat stress during summer season. The body temperature, respiration and pulse rates have decreased as a result of the use of cold water or supply of ascorbic acid. Therefore, availability of cold water is paramount to prevent heat stress in sheep, especially during periods of extended hot and humidity.

Water and feed intake responses of sheep to drinking water temperature in hot conditions

When live-export sheep from Australia arrive in the Middle East during the northern summer months, they may be offered drinking water at temperatures exceeding 40°C. There is little published research to indicate whether drinking water temperature is important in managing heat stress in sheep or its effect on their health and welfare. Three studies were conducted with Merino wethers in climate-controlled rooms to investigate: (i) responses to drinking water temperatures of 20°C, 30°C and 40°C in a cool (20°C) and hot (40°C) environment, (ii) preferences for drinking water temperature at 20°C or 30°C when in a hot or cool environment and (iii) effects of water restriction when offered hot water (40°C) in a hot environment. Sheep assigned to the hot room had significantly higher respiration rates than those assigned to the cool room. In the cool environment, water intakes were the same when water temperatures were 20°C, 30°C or 40°C; however, when the sheep were given a choice between drinking water at 20°C and 30°C, they preferred (P &lt; 0.05) to drink water at 20°C. In the hot environment, water intake increased as drinking water temperature increased, and sheep preferred to drink water at 30°C rather than 20°C. When the availability of 40°C drinking water was restricted (to ~10% of liveweight) in the hot environment, sheep had higher respiration rates than those offered unlimited water.