Prepartal dietary cobalt source alters holstein calf semitendinosus muscle abundance of mTOR and insulin signaling proteins and intermediates of one-carbon metabolism

Requirement for Cobalt and folic acid (FOA) in late-pregnant dairy cows is unknown, but dietary supply of one or both could impact activity of onecarbon metabolism. Holstein cows were fed the same basal diet supplemented with Cobalt glucoheptonate (CoPro, n =16) or a slow-release Cobalt polysaccharide (CoPectin, n = 14) for the last 30 days prepartum to assess impacts on calf growth and skeletal muscle metabolism. Cobalt treatments delivered 1 ppm Cobalt/kg DM and both diets supplied 50 mg ruminallyavailable FOA/day. Calves were weighed at birth and growth performance recorded weekly through 9-weeks of age. Prior to weaning (day 42), calves (n = 7 and 8 for CoPro and CoPectin group, respectively) were subjected to biopsy of semitendinosus muscle for Western blotting and targeted metabolomics using LC-MS-MS. Although birth measures of development did not differ (P > 0.05), calves born from CoPectin cows had greater hip width (HW) at weeks 8–9 (Diet×Time, P = 0.03). Overall, withers height (WH) tended (84.6 vs. 82.4 ± 0.9 cm; P = 0.10) to be greater in CoPectin than CoPro calves. Metabolomic profiling revealed greater concentrations of betaine (5.11 ± 0.36 × 106 vs. 4.12 ± 0.36 × 106 AUC; P = 0.04) and S-adenosylmethionine (3.87 ± 0.42 × 106 vs. 2.61 ± 0.42 × 106 AUC; P = 0.02), with tendencies for greater cystathionine (1.02 ± 0.10 × 106 vs. 0.71 ± 0.10 × 106 AUC; P = 0.06) and choline (8.04 ± 1.15 × 106 vs. 5.83 ± 1.15 × 106 AUC; P = 0.10) in CoPectin compared with CoPro calves. Protein abundance (relative to GAPDH) of INSR (1.34 ± 0.07 vs. 1.12 ± 0.05; P = 0.05), p-AKT (1.22 ± 0.08 vs. 1.01 ± 0.06; P = 0.05), and p-AKT : AKT ratio (1.37 ± 0.09 vs. 1.00 ± 0.07; P = 0.001) were greater, whereas total 4EBP1 (0.81 ± 0.06 vs. 1.03 ± 0.05; P = 0.03) and MRF4 (0.75 ± 0.05 vs. 0.96 ± 0.07; P = 0.04) were lower in CoPectin calves. These results suggest that the slow-release cobalt source (CoPectin) enhanced maternal cobalt utilization and fetal one-carbon metabolism, leading to greater activation of the insulin–AKT–mTOR pathway in calf skeletal muscle. Further research could help determine the degree to which slow-release Cobalt alters ruminal synthesis of vitamin B₁₂ and its impact on the physiology of the neonatal calf.