Heat stress (HS) threatens the worldwide dairy industry by decreasing animal production performance and health. Holstein cows and dairy buffaloes are the most important dairy animals, but their differences in the metabolic mechanism of thermotolerance remain elusive. In this study, we used serum metabolomics to evaluate the differences in thermotolerance between Holstein cows and crossbred dairy buffaloes under chronic heat stress (HS) and thermal-neutral conditions. In response to HS, the body temperatures and respiratory rates were increased more for Holstein cows than for dairy buffaloes (38.78 vs 38.24 °C, p < 0.001; 43.6 vs 32.5 breaths/min, p < 0.001). HS greatly affected serum metabolites associated with amino acids, fatty acids, and bile acids. The enriched metabolic pathways of these serum metabolites are closely related to HS. We demonstrated that buffaloes adapt to HS by adopting a metabolism of branched-chain amino acids and ketogenic amino acids and gluconeogenesis, but Holstein cows decrease the effect of HS with citrulline and proline metabolism. Both physiological parameters and serum metabolic profiles indicate that dairy buffaloes are more thermotolerant than Holstein cows, providing the feasibility to vigorously develop the buffalo dairy industry in tropical and subtropical regions.

Shade shelter is widely used to reduce heat load for farm animals, but little research focus on the cooling effects for Dehong buffalo calves. The aim of this experiment was to evaluate the impacts of shade cooling on the physiological and behavioural parameters for Dehong buffalo calves. Shade with 99% blockage of solar radiation was covered on steel frame with a 2.5 m height above the loafing area floor (Shaded). The loafing area of the control group was the same as the shaded group, © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ apart from no shade shelter above the loafing area (non-shaded). Twenty-four Dehong buffalo calves were randomly and averagely allocated to the non-shaded and shaded groups. Six Dehong buffalo calves were loose housed in a barn, and they had access to loafing area. The results showed that the average daily air temperature of the loafing area under shade was lower 1.5 than that of the non-shaded loafing area. No difference in rectal temperature was found between the non-shaded and shaded calves (P > 0.05), but respiration rate of the non-shaded group in noon (12:00h, 31.6 breaths) and evening (18:00h, 28.5 breaths) was greater than for calves in shaded group (26.1 and 25.3 breaths, respectively) (P < 0.05). When ambient temperature exceeded 30 , shaded calves spent much of their time (21.7%) lying in the loafing area, and no calf in non-shaded group preferred to lie in the loafing area with strong solar radiation (P < 0.05). The use of shade for calves was affected by thermal environment, and the use of shade was greater (41.4%) in hot weather (above 30 ) than that of the warm weather (22-29 ) (P < 0.05). In conclusion, the provision of shade above the loafing area is conducive to improving thermal environment for Dehong buffalo calves in subtropical area characterized with high ambient temperature coupled with high humidity in summer.

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