Heat stress affects some physiological and productive variables and alters metabolism in dairy ewes

Abstract

Heat stress (HS) has a significant economic impact on the global dairy industry. However, the mechanisms by which HS negatively affects metabolism and milk synthesis in dairy ewes are not well defined. This study evaluated the production and metabolic variables in dairy ewes under controlled HS conditions. Eight Lacaune ewes (75.5 ± 3.2 kg of body weight; 165 ± 4 d of lactation; 2.31 ± 0.04 kg of milk per day) were submitted to thermoneutral (TN) or HS conditions in a crossover design (2 periods, 21 d each, 6-d transition). Conditions (day-night, 12-12 h; relative humidity; temperature-humidity index, THI) were: TN (15-20°C; 50 ± 5%; THI = 59-65) and HS (28-35°C; 45 ± 5%; THI = 75-83). Ewes were fed ad libitum and milked twice daily. Rectal temperature, respiratory rate, feed intake, water consumption, and milk yield were recorded daily. Milk and blood samples were collected weekly. Additionally, TN and HS ewes were exposed to glucose tolerance test, insulin tolerance test, and epinephrine challenge. Heat stress reduced feed intake (−11%), and increased rectal temperature (+0.77°C), respiratory rate (+90 breaths/min), and water consumption (+28%). Despite the reduced feed intake, HS ewes produced similar milk to TN ewes, but their milk contained lower fat (−1.7 points) and protein (−0.86 points). Further, HS milk tended to contain more somatic cells (+0.23 log points). Blood creatinine was greater in HS compared with TN, but no differences in blood glucose, nonesterified fatty acids, or urea were detected. When glucose was infused, TN and HS had similar insulin response, but higher glucose response (+85%) was detected in HS ewes. Epinephrine infusion resulted in lower nonesterified fatty acids response (−215%) in HS than TN ewes. Overall, HS decreased feed intake, but milk production was not affected. Heat stress caused metabolic adaptations that included increased body muscle degradation and reduced adipose tissue mobilization. These adaptations allowed ewes to spare glucose and to avoid reductions in milk yield.

Effects of High Heat Load Conditions on Blood Constituent Concentrations in Dorper, Katahdin, and St. Croix Sheep from Different Regions of the USA

“…The lowest concentration of CRT among periods in period 1 may reflect minimal protein catabolism with thermoneutral conditions. Similarly, thermal challenges to dairy ewes [ 45 ] and goats [ 46 ] increased blood CRT concentration, suggesting that heat stress causes muscle degradation. That the level of TP was lower in period 4 vs. 1 despite this difference in CRT could involve relatively high water intake and body water content in period 4.…”

Adaptive Capability of Wahati Sheep and Goats Flocks to ‎desert Oasis Conditions in the New Valley of Egypt

“…Barki sheep practiced more deep breathing to cope with the needed energy for physical exercise under heat stress, than Barki Goats. Mehaba, et al (2021) reported significant increase in RR and GV in heat stressed dairy ewes, compared to that under thermo-neutral conditions. GV (l/min) 2.1b ± 0.05 (1.0-3.4)…”

Thermoregulatory reactions of female buffaloes raised in the sun and in the shade, in the climatic conditions of the rainy season of the Island of Marajó, Pará, Brazil

“…Climatic variables can affect metabolism, and consequently, surface temperature and rectal temperature in buffaloes ( 47 ), as well as in Nelore ( 48 ) and dairy cows ( 49 , 50 ).…”