In utero heat stress alters the offspring epigenome [methylation]

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 Reduced Representation Bisulfite Sequencing, this study evaluated DNA methylation of liver and mammary gland of bull calves and heifers that were gestated under maternal conditions of heat stress or cooling, i.e., in utero heat stressed (HT) vs. in utero cooled (CL). Liver samples from bull calves (CT = 5 and HT = 4) were collected at birth while mammary gland samples from heifers (CT = 3 and HT = 3) were collected during their first lactation. Nine bull calves and six heifers 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. Both bull calves (HT = 4 and CL = 5) and 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. Liver samples were collect from bull calves inmediately after birth. Heifers were managed under identical conditions from birth through their first lactation and mammary gland samples were collected on day 21 of the first lactation, coinciding with the rising milk yield phase of the lactation cycle. Liver and mammary gland samples were subjected to DNA extraction and subsequent reduced representation bisulfite sequencing.