Dam prepartum skeletal muscle reserves and supplementation with branched-chain volatile fatty acids during late gestation influence calf birth weight and calf muscle metabolic activity.

Dairy cattle mobilize skeletal muscle in the periparturient period to close energy and metabolizable protein gaps due to the high demands of the growing fetus and milk production. The objective of this study was to determine if the amount of dam prepartum muscle reserves and branched-chain volatile fatty acids (BCVFA) supplementation affected calf birth weight, calf circulating AA, calf semitendinosus muscle metabolic activity, and colostrum composition. We hypothesized that calves born to dams with higher prepartum muscle reserves and supplemented with BCVFA would be heavier, have greater muscle mass as determined by circulating creatinine, and have higher muscle metabolic activity compared with calves born to low-muscle dams not supplemented with BCVFA. At 42 d before expected calving (BEC), the depth of the longissimus dorsi muscle was measured via ultrasound and cows were classified as high muscle (HM; >4.6 cm) or low muscle (LM; ≤4.6 cm) and then randomly assigned to either control (CON) diet, which consisted of soy hulls or calcium salt products of BCVFA that were top dressed from 42 d BEC to parturition. The final study design was a 2 × 2 factorial of muscle reserves and BCVFA supplementation, resulting in LM-CON (n = 8), LM-BCVFA (n = 10), HM-CON (n = 12), and HM-BCVFA (n = 10). Calves were weighed and colostrum was fed to calves at 10% of birth BW and a second dose at 5% of birth BW. At 24 h postnatal, a jugular blood sample and biopsy from the semitendinosus muscle was collected. Metabolic activity of the semitendinosus muscle was measured with a resazurin based assay. Calves born to HM cows were heavier at birth and had higher circulating creatinine and higher muscle metabolic activity, but dam BCVFA supplementation did not affect any of these parameters. Neither maternal muscle reserves nor BCVFA affected calf muscle mTOR abundance or phosphorylation state, although LM-CON calves tended to have lower phosphorylated mTOR than other groups. The greater birth weight, greater circulating creatinine, and higher muscle metabolic activity of calves born to HM cows suggest that maternal muscle reserves influence fetal growth and muscle mass as well as muscle metabolic phenotype.