Deciphering the mammary gland transcriptome during the dry period in dairy cows under heat stress

The bovine dry period is a dynamic non-lactating phase where the mammary gland undergoes extensive tissue remodeling. Utilizing RNA Sequencing, this study characterized novel genes and pathways involved in this process and determined the impact of dry period heat stress. Mammary tissues were collected before and during the dry period (-3, 3, 7, 14, and 25 days relative to dry-off) from twelve heat-stressed (HT, n=6) or cooled (CL, n=6) pregnant Holstein cows. Twelve multiparous Holstein cows were dried off at 46 d before expected calving. Cows were randomly assigned to two treatments for the duration of the dry period: heat-stressed (HT, n=6; access to shade) or cooled (CL, n=6; access to shade, fans and soakers). Mammary biopsies were collected from the same cow at day 3 before dry-off and at day 3, 7, 14, and 25 after dry-off. Mammary tissue samples (12 cows x 5 time points = 60 samples) were subjected to RNA extraction, library generation, and subsequent sequencing.