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 one-carbon 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 ruminally-available 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.