PSIV-A-4 Characterization of Heat Stress and Recovery on Productive Performance and Physiological Indicators, Blood and Milk Characteristic, and Gene Expression in Early Lactating Holstein Cows

We aimed to characterize the novel insights into the recovery (RC) regulation mechanism after heat stress (HS) in early lactating Holstein cows in changing environments using measures of productive performance, physiological and genetic indicators, and blood and milk parameters. Twelve cows (milk yield = 23.64 ± 0.88 kg/d, days in milk = 57 ± 3 d) were randomly and equally housed in environmentally controlled chambers by providing temperature-humidity index (THI) at three levels of 72~73 (25oC, 50~60% humidity, Comfort), 78~79 (28oC, 60~70% humidity, Mild), and 86~87 (31℃, 80~90% humidity, Moderate). The environments inside the chambers were adjusted for 3 days of adaptation at 67~68 THI (22℃, 50~60% humidity, normal) level. After adaptation, cows were received HS for 7 days and RC for 5 days. Data were analyzed using the mixed procedure of SAS. Feed intake and milk yield were lower and water intake was higher in the Moderate than the Comfort and Mild groups (p < 0.05). Concentration of milk beta-casein was lower (p < 0.05) in the Moderate than those of Comfort whereas numerical increase in RC of each group was observed. In Moderate group, blood glucose was lower and NEFA was higher than those of Comfort while cortisol decreased in RC (p < 0.05). Rectal temperature in Moderate was higher than the Comfort and Mild groups and decreased during RC (p < 0.05). Blood HSP70 and HSPB1 in Moderate and Mild groups were higher than those of Comfort (p < 0.05) and numerical decreased in RC of Moderate group. In conclusion, early lactating Holstein cows showed negative effects on productive performance, blood and milk characteristics, physiological, and genetic indicators at moderate level and had a lower RC rate. Considering that the RC rate decreases under higher THI, establishing customized breed management strategies to deal with negative effects of HS at different levels for accelerating RC are pivotal.