PSIV-4 - Characterization of heat stress condition on productive performance and physiological indicators, milk composition, gene expression, and metabolomics in blood and milk of early lactating Holstein cows

We aimed to characterize heat stress (HS) effects in early lactating Holstein cows using measures of productive performance, physiological and genetic indicators, blood and milk parameters, and metabolomics in blood and milk. Eight cows (milk yield = 29.27 ± 0.38 kg/d, days in milk = 40 ± 8 d) were equally housed in environmentally controlled chambers by providing temperature-humidity index (THI) at two levels of 70~71 (25℃, 35~50% humidity, threshold) and 86~87 (31℃, 80~95% humidity, severe). For each treatment, the environment inside the chamber was adjusted for 7 days of adaptation at 67~68 THI (22℃, 50~60% humidity, normal) level. After the adjustment period, cows were subjected to HS for 7 days. Feed and water intake and milk yield were measured daily, and blood was collected and physiological indicators were monitored on the 7^th and 14^th days. Data were analyzed using GLM procedure of SAS. Feed intake and milk yield were lower (P < 0.05) and water intake was higher (P < 0.05) in the severe than the threshold and normal. Lactose tended to be lower (P = 0.082) in the severe than the threshold and normal. Heart rate, rectal and skin temperature were higher (P < 0.05) in the severe than the threshold and normal. Blood HSP90 and HSPB1 were higher (P < 0.05) in the severe than threshold and normal. Alanine, proline, glutamic acid, tryptophan, lactic acid, and citric acid in milk and blood were lower (P < 0.05) in the severe than threshold and normal. In conclusion, early lactating Holstein cows are characterized to receive higher HS by showing the changes in historical measures of productive performance, physiological and genetic indicators, and blood and milk parameters under severe HS condition whereas the new approach of metabolomics in blood and milk are recognized as sensitive and reliable indicators of severe HS.