227 Moderate body weight loss reduces total antioxidant capacity in pregnant beef heifers and one-carbon metabolite supplementation does not mitigate this response

Abstract In beef heifers, body weight (BW) gain and physiological stress are important considerations for reproductive outcomes and whole herd production efficiencies. The objective of this study was to determine if dietary one-carbon metabolite (OCM) supplementation in moderate BW loss pregnant heifers alters circulating total antioxidant capacity, superoxide dismutase, and glutathione peroxidase activity. In a replicated 2 × 2 factorial, Angus-cross heifers (n = 81) were stratified by BW to gain 0.45 kg/d (CON) or lose 0.23 kg/d (RES) and receive corn carrier with OCM supplements (+OCM) or without (−OCM). The OCM supplements consisted of vitamin B12 (20 mg) and folate (320 mg) injections weekly and dietary rumen-protected methionine (7.4 g/d) and choline (44.4 g/d) from breeding (d 0) to d 63 of gestation. The four treatment groups were: CON−OCM (n = 20), CON+OCM (n = 21), RES−OCM (n = 21), and RES+OCM (n = 19). Heifers underwent estrus synchronization and were bred via artificial insemination using female sexed semen to a single sire. Pregnancy was diagnosed and fetal sex was verified on d 35 of gestation. Blood was collected and assayed for total antioxidant capacity, superoxide dismutase, and glutathione peroxidase activity on d −2 (baseline), 35, and 63 of gestation for all three replicates. Data were analyzed using the MIXED procedure of SAS with repeated measures to determine the effect of gain, supplement, day, and their two-way and three-way interactions. The gain × supplement interaction remained in all models, but other interactions were removed if P > 0.10. Replicate and heifer BW were included in the model as covariates and covariance structure was determined by lowest AIC and BIC. Statistical significance was considered at P ≤ 0.05 and tendencies at 0.05 < P ≤ 0.10. There was no BW gain × supplement interaction, or main effect of OCM supplements in total antioxidants. There was a gain × day effect (P ≤ 0.01), in which total antioxidants were increased on d 35 and further increased on d 63 in CON compared with RES treatments. There was no gain × supplement interaction, or main effect of gain or OCM supplements in superoxide dismutase and glutathione peroxidase. However, both superoxide dismutase and glutathione peroxidase were decreased (P ≤ 0.01) on d 63 compared with d 0 and 35. These data suggest that moderate BW loss reduces total antioxidant capacity in pregnant beef heifers, which could affect redox homeostasis. However, OCM supplements did not affect total antioxidant capacity, superoxide dismutase, or glutathione peroxidase. These findings are somewhat surprising considering oxidative stress has been well characterized in nutrient-restricted pregnancies, and given the interconnection between energy metabolism and one-carbon metabolism. Future research is warranted to fully elucidate the therapeutic effects of one-carbon metabolites.