In utero heat stress alters the offspring epigenome

Exposure to intrauterine heat stress during late gestation affects offspring performance into adulthood. However, underlying mechanistic links between thermal insult in fetal life and postnatal outcomes are not completely understood. Utilizing RNA Sequencing, this study characterized the mammary gland transcriptome of heifers that were gestated under maternal conditions of heat stress or cooling, i.e., in utero heat stressed (HT) vs. in utero cooled (CL). Mammary tissues were collected from three HT and three CL heifers during their first lactation. Six heifers (all born in 2014) gestated under maternal conditions of heat stress (HT, dams had access to shade) or cooling (CL, dams had access to shade, fans and soakers) were used for this study. These six heifers (HT = 3 and CL = 3) were exposed to the maternal treatment through the intrauterine environment during the last 6-7 weeks of fetal development. All the heifers were managed under identical conditions from birth through their first lactation in summer 2016. Mammary gland biopsies were collected on day 21 of the first lactation, coinciding with the rising milk yield phase of the lactation cycle. Mammary tissue samples were subjected to RNA extraction, library generation, and subsequent sequencing.