One-carbon metabolite supplementation to heifers for the first 14 d of the estrous cycle alters the plasma and hepatic one-carbon metabolite pool and methionine-folate cycle enzyme transcript abundance in a dose-dependent manner

The objective of this study was to determine the dose of folate and vitamin B12in beef heifers fed rumen protected methionine and choline required to maintain increased B12levels and intermediates of the methionine-folate cycle in circulation. Angus heifers (n = 30; BW = 392.6 ± 12.6 kg) were individually fed and assigned to one of five treatments: 0XNEG: Total mixed ration (TMR) and saline injections at day 0 and 7 of the estrous cycle, 0XPOS: TMR, rumen protected methionine (MET) fed at 0.08% of the diet DM, rumen protected choline (CHOL) fed at 60 g/d, and saline injections at day 0 and 7, 0.5X: TMR, MET, CHOL, 5 mg B12, and 80 mg folate at day 0 and 7, 1X: TMR, MET CHOL, 10 mg vitamin B12, and 160 mg folate at day 0 and 7, and 2X: TMR, MET, CHOL, 20 mg B12, and 320 mg folate at day 0 and 7. All heifers were estrus synchronized but not bred, and blood was collected on day 0, 2, 5, 7, 9, 12, and 14 of a synchronized estrous cycle. Heifers were slaughtered on day 14 of the estrous cycle for liver collection. Serum B12concentrations were greater in the 0.5X, 1X, and 2X, compared with 0XNEG and 0XPOS on all days after treatment initiation (P< 0.0001). Serum folate concentrations were greater for the 2X treatment at day 5, 7, and 9 of the cycle compared with all other treatments (P≤ 0.05). There were no differences (P≥ 0.19) in hepatic methionine-cycle or choline analyte concentrations by treatment. Concentrations of hepatic folate cycle intermediates were always greater (P≤ 0.04) in the 2X treatment compared with the 0XNEG and 0XPOS heifers. Serum methionine was greater (P= 0.04) in the 0.5X and 2X heifers compared with 0XNEG, and S-adenosylhomocysteine (SAH) tended (P= 0.06) to be greater in the 0.5X heifers and the S-adenosylmethionine (SAM):SAH ratio was decreased (P= 0.05) in the 0.5X treatment compared with the 0XNEG, 0XPOS, and 2X heifers. The hepatic transcript abundance of MAT2Aand MAT2Bwere decreased (P≤ 0.02) in the 0.5X heifers compared with the 0XNEG, 0XPOS, and 2X heifers. These data support that beef heifers fed rumen protected methionine and choline require 20 mg B12and 320 mg folate once weekly to maintain increased concentrations of B12and folate in serum. Furthermore, these data demonstrate that not all supplementation levels are equal in providing positive responses, and that some levels, such as the 0.5X, may result in a stoichiometric imbalance in the one-carbon metabolism pathway that results in a decreased SAM:SAH ratio.This study determined the optimal doses for vitamin B12(20 mg injected weekly) and folate (320 mg injected weekly) injection to beef heifers during the periconceptual period when rumen protected methionine and choline were fed at 0.08% of dry matter and 60 g/d, respectively. These doses set the basis upon which future studies can be based when feeding and injecting one-carbon metabolites.The strategic inclusion of one-carbon metabolites, which include vitamins and minerals that are found in human prenatal vitamins, to beef cattle feeding and management protocols during the periconceptual period (the time around breeding) is a novel concept. Therefore, this study aimed to identify the feeding and injection doses of one-carbon metabolites in beef heifers to maintain increased circulating concentrations of one-carbon metabolites for use as a model from which other studies could base their treatments on. We determined that daily feeding of methionine and choline at 0.08% of dry matter and 60 g/d, respectively, and administration of vitamin B12and folate at 20 mg and 320 mg once per week, respectively resulted in sustained elevated concentrations of one-carbon metabolites.