PSVIII-29 - Nutritional epigenetic modifications in beef cattle

Abstract: Nutrition of the beef cow during pregnancy influences fetal development and potential changes in phenotype. On average 9-10% of the beef cattle herd are below the optimal body condition score of 2.5/5 at both pre-breeding and pregnancy tests, indicating potential nutritional stress during gestation. Epigenetic modifications are reported to regulate the changes in phenotype due to maternal nutrition during gestation. Our objective was to evaluate the influence of maternal nutrition during gestation on possible epigenetic mechanisms regulating development and biological function in Longissimus dorsi (LD) and Semimembranosus (SM) muscles, and liver (LV) at slaughter in steer progeny born from dams fed two different planes of nutrition during gestation. We also wanted to explore if the offspring's genetic potential for residual feed intake (RFI) would interact with prenatal maternal diet to have differential effects on these epigenetic mechanisms. Purebred Angus steer calves (n=23) were born from dams which were fed a diet formulated for an average daily gain (ADG) of either 0.5 or 0.7 kg/d from 30-150 days of gestation. Mating was designed so that calves were born from parents with differential genetic potential for high or low RFI. Calves were raised together as per normal industry standards and fed to be slaughtered as a finished steers at approximately 512.1 ± 10.1 days of age. One approximately 10 g sample each of LV, LD, and SM muscles was aseptically collected within 30–45 min post-mortem and snap frozen in liquid nitrogen and subsequently stored at -80°C. Both DNA and RNA were isolated from the tissue samples and investigated for differences in methylation and gene expression, respectively. Fifteen potentially differently methylated regions (DMRs) in the DNA were measured using EpiTYPER MassARRAY technology, while expression of genes corresponding to the potential DMRs was measured by the nCounter Element Tagset by NanoString technologies. Average methylation across each DMR as well as gene expression within each tissue was profiled using principal component analyses (PCA). Distinct clustering was seen within both DNA methylation and gene expression PCAs such that the two muscles were clustered together and were separate from DNA methylation and gene expression measured in LV, representing expected functional variation due to tissue type. Between LD and SM, methylation patterns in the two muscles overlap, while there is much less overlap in gene expression patterns. This implies that the methylation pattern between the two muscle types is relatively similar compared their patterns in gene expression, and that smaller differences in DNA methylation lead to relatively larger differences in gene expression. These analyses are an important first step to interrogate the quality of our data that will be further analyzed for responses to maternal diet treatment and selection for genetic potential for RFI.