School of Agriculture, Food and Ecosystem Sciences - Research Publications
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Item275 Access to Shade Mitigate Heat Stress and Improves Growth Performance in Lambs During Summer(Oxford University Press (OUP), 2021-10-08)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) >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 (> 60% in both groups). However, high temperature (T > 30°C) decreased grazing behavior in sheep to < 5% in both treatments. Standing behavior was significantly greater (65.2 vs 21.6%; P < 0.05) for animals under non-shade treatment, while lying behavior was more frequent (17.3 vs 76.3%; P < 0.01) in animals having access to shade. Significantly more animals were seeking water troughs (P < 0.05) in the non-shade group (33.2%) compared to the shade group (10.3%). On an average hot day (T >28°C), most lambs in the shade group were seeking shade (P < 0.01), and when the temperature exceeded >32°C, 90% of the lambs were seeking tree shade. Sheep with access to shade exhibited lower (P < 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 < 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.
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ItemAccess to Shade Mitigate Heat Stress and Improves Growth Performance in Lambs During Summer(American Society of Animal Science, 2021)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) >30°C). Behavioral patterns were represented as the proportion of animals doing specific activities in each treatment group.
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ItemAdaptive and Productive Sheep Breed for Changing Climate(MDPI, 2020-04-01)Sheep in semi-arid environments are likely to be affected by warming environment due to climate change. To identify genotypes best suited to warmer climates we assessed thermotolerance and meat quality of 5 female sheep of each of 4 breeds (Merino, Wiltshire, Dorper, and Southdown) under simulated summer conditions. The sheep were housed in metabolic crates within climate-controlled rooms and were exposed to thermo-neutral (TN; 18–21 °C and 40–50% relative humidity) or cyclic heat stress (HS; 28–40 °C and 30–40% RH) conditions for two weeks. Physiological responses were recorded 3 times daily, and brown fat tissue temperature was measured by data loggers inserted into the brisket. Sheep were slaughtered at an abattoir as per standard commercial procedure and samples obtained for carcass and meat quality attributes. When exposed to HS, Dorpers and Merinos exhibited lower respiration rate (151, 142 breaths/min, respectively) and rectal temperature (39.39, 39.32 °C, respectively) (P < 0.05) than Southdowns (192 breaths/min, 40.05 °C) and Wiltshires (200 breaths/min, 39.91 °C). Dorper and Wiltshire (n = 3) showed lowest sternal fat temperatures during HS indicating inherent differences in thermogenesis. HS had significant effect (P < 0.05) on post mortem muscle pH decline which was slower than TN sheep, except in Dorper again indicating better thermotolerance. There were significant (P = 0.03) breed effects on meat cooking loss % such that Southdown showed minimum cooking loss (17%) while Merino showed the greatest loss (24%). These results suggest that there are genetic (breed) differences in thermotolerance and meat quality of sheep, providing an opportunity to select best sheep suited to a warming climate.
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ItemDifferences in Thermoregulatory Responses between Dorper and Second Cross Lambs to Heat Stress Challenges(MDPI, 2020-04-07)We compared the thermotolerance of Dorper (D) and second cross (SC) (Poll Dorset x Merino/Border Leicester) lambs by assessing physiological and biochemical responses. After acclimatization, 4–5 month old lambs of each breed were exposed to either thermo-neutral (18 °C–21 °C, 40%–50% RH, n = 12/group) or cyclic heat stress (HS) (28 °C–40 °C; 40%–60% RH, n = 12/group) for 2 weeks in climatic chambers. The HS involved exposure to temperatures of 38 °C–40 °C between 0800 and 17.00 h daily; otherwise the temperature was maintained at 28 °C. Elevated temperature increased rectal temperature (p < 0.01), respiration rate (p < 0.01) and skin temperature (p < 0.01) in both breeds, (data for 12.00 and 16.00 h pooled), but to a lesser extent in D than in SC lambs (p < 0.01). The HS increased (p < 0.01) water intake to a greater extent in SC than in D lambs and HS reduced (p < 0.05) food intake in SC lambs but not in D lambs. There were no treatment effects on blood glucose and lactate levels in either breed. Significant effects of breed (p < 0.01) and treatment (p < 0.01) were observed in blood creatinine levels, being higher in SC lambs. Higher pH (p < 0.01) and lower pCO2 (p < 0.01) were recorded under HS in both breeds. Among blood electrolytes, Cl−, Na+ and base excess were significantly (all p < 0.01) reduced under HS, with no breed differences. In conclusion, the attenuated physiological responses to HS in Dorper lambs indicates better adaptation of this breed to high environmental temperature.
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ItemComparative Assessment of Thermotolerance in Dorper and Second-Cross (Poll Dorset/Merino x Border Leicester) Lambs(MDPI, 2020-12)The objective of this study was to compare the thermotolerance of second-cross (SC; Poll Dorset × Merino × Border Leicester) and Dorper lambs. Dorper and SC lambs (4-5 months of age) were subjected to cyclic heat stress (HS) (28-40 °C). The temperature was increased to 38-40 °C between 800 and 1700 h daily and maintained at 28 °C for the remainder of the day (30-60% relative humidity (RH)) in climatic chambers for 2 weeks (n = 12/group), with controls maintained in a thermoneutral (TN) (18-21 °C, 40-50% RH) environment (n = 12/group). Basal respiration rate (RR), rectal temperature (RT) and skin temperature (ST) were higher (p < 0.01) in SC lambs than in Dorpers. HS increased RR, RT and ST (p < 0.01) in both genotypes, but the levels reached during HS were lower (p < 0.01) in Dorpers. HS increased (p < 0.01) water intake to a greater extent in SC lambs, while feed intake was reduced (p < 0.05) by HS in SC lambs but not in Dorpers. HS increased (p < 0.01) blood urea nitrogen and creatinine in SC lambs only. Plasma non-esterified fatty acid concentrations were reduced (p < 0.05) by HS in SC lambs but increased (p < 0.05) in Dorpers. There was no effect of HS on pO2, cHCO3- and cSO2, but higher (p < 0.01) blood pH and lower (p < 0.01) pCO2 were recorded under HS in both genotypes. Blood electrolytes and base excess were reduced (p < 0.01) under HS, while a genotype difference (p < 0.05) was only observed in blood K+ and hemoglobin concentrations. Basal plasma prolactin concentrations were lower (p < 0.01) in Dorpers but were elevated at a similar level during HS (p < 0.01) in both genotypes. Dorper lambs are more resilient to HS than SC lambs. Future research should focus on confirming whether the better heat tolerance of Dorpers is translated to better returns in terms of growth performance and carcass traits over the summer months.
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ItemResilience of Small Ruminants to Climate Change and Increased Environmental Temperature: A Review(MDPI, 2020-05)Climate change is a major global threat to the sustainability of livestock systems. Climatic factors such as ambient temperature, relative humidity, direct and indirect solar radiation and wind speed influence feed and water availability, fodder quality and disease occurrence, with production being most efficient in optimal environmental conditions. Among these climatic variables, ambient temperature fluctuations have the most impact on livestock production and animal welfare. Continuous exposure of the animals to heat stress compromises growth, milk and meat production and reproduction. The capacity of an animal to mitigate effects of increased environmental temperature, without progressing into stress response, differs within and between species. Comparatively, small ruminants are better adapted to hot environments than large ruminants and have better ability to survive, produce and reproduce in harsh climatic regions. Nevertheless, the physiological and behavioral changes in response to hot environments affect small ruminant production. It has been found that tropical breeds are more adaptive to hot climates than high-producing temperate breeds. The growing body of knowledge on the negative impact of heat stress on small ruminant production and welfare will assist in the development of suitable strategies to mitigate heat stress. Selection of thermotolerant breeds, through identification of genetic traits for adaption to extreme environmental conditions (high temperature, feed scarcity, water scarcity), is a viable strategy to combat climate change and minimize the impact on small ruminant production and welfare. This review highlights such adaption within and among different breeds of small ruminants challenged by heat stress.