Transcriptome profiling in the mammary tissue of dairy cows under heat stress and thermal neutral conditions

Milk protein is one of the necessary protein sources in human diet, and milk protein concentration is of great significance for the dairy industry. However, as consequence of heat stress conditions milk yield is decreased with an even larger decrease in protein yield. It has long been recognized that the changes in milk yield and composition from heat stress are at least partly a result of the sudden depression of feed intake. However, using the pair-fed design, when the dry matter intake (DMI) of the two treatments was identical, the milk protein content and milk protein yield of the heat-stressed (HS) cows was still lower than the cows raised in pair-fed thermal neutral (PFTN) conditions. The decline of DMI could only account for 65% of the decrease of milk protein yield, while the reasons of the remnant 35% milk protein yield decline remained unaccounted for.The decrease of protein synthesis appears to be the result of downregulation of mammary protein synthetic activity. However, it remains to be determined what specifically drives the reduced milk protein synthesis in mammary gland under heat stress conditions. The goal of this study is to detect the transcriptomes changes in the heat-stressed cows' mammary tissue and find additional reasons for the declined milk protein yield of heat-stressed cows