Effects of Post-Insemination Dam Nutrition on Calf Performance and DNA Methylation

Nutritional changes immediately after insemination can result in increased embryonic mortality, but the impact of a nutritional change on the embryos that survive is not known. Therefore, the objective of this study was to evaluate the impact of a nutritional change immediately following AI on calf performance and global DNA methylation. Calving records were obtained for 142 heifers over two yr that were allotted into two developmental treatments: drylot or range. All heifers were fixed-time inseminated following the 7-day CO-Synch plus CIDR protocol to a single sire each year and were turned out to pasture together and managed as a single group. Pregnancy success to AI was determined via ultrasonography, and calving data (calving date, birth weight, sex, and weaning weight) were collected. DNA was obtained from calves at weaning, and analyzed for global methylation (total methylation and 5-hmC methylation). Data were analyzed as a 2x2 factorial design using the mixed procedure in SAS with sex and replicate included in the model. Bull calves were heavier at birth compared to heifer calves (P=0.04; 34.9±0.45 vs 34.3±0.60 kg) and both bull-bred calves (35.7±0.4 kg) and range (35.3±0.5 kg) calves were heavier (P<0.01) at birth compared to AI-sired (32.9±0.5) and drylot (33.3±0.5 kg) calves. However, there was no replicate (P=0.99) or development by sire interaction (P=0.70). For weaning weights both development (P=0.04) and sire (P<0.01) impacted weaning weights with AI sired calves (221.8±5.1 vs 189.1±2.7 kg) and range developed (210.6±3.6 vs 200.2±3.4 kg) calves being heavier. Sex tended (P=0.09) to influence weaning weight, but there was no development by sire interaction (P=0.99). Total DNA methylation was not effected by development (P=0.34), sex (P=0.21), sire (P=0.24), or any interactions (P>0.70). For 5-hmC methylation there was a tendency for both development method and sex of the calf to impact global methylation, with range and bull calves tending (P=0.10) to have decreased methylation compared to drylot and heifers. In addition there was a sire by development (P<0.01) and sire by sex (P=0.05) interaction with bull-bred drylot developed calves having greater methylation than all other groups and with AI-sired bull calves having decreased methylation compared to AI-sired heifer and bull-bred bull calves. In summary, method of heifer development and sire can impact future performance of the calf that is in utero as determined by BW and WW, and this change in performance may be regulated through DNA methylation.