PSXIV-5 - Methionine supply during mid-gestation affects offspring birth weight in a sex-dependent manner in beef cattle

In previous studies with dairy cattle, methionine supply during late-gestation enhanced cow feed intake and affected calf growth in utero and postnatally. Our objective was to investigate how methionine supply during mid-gestation, phase where the secondary myogenesis occurs, alters heifers’ plasma concentration of amino acids and offspring’ birth weight in beef cattle. Forty purebred Angus heifers were blocked by expected parturition day and blocks were balanced by sire, body weight, and body condition score. Heifers were randomly assigned to a basal diet with no added methionine (Control) or the basal diet plus a commercial source of rumen-protected methionine (Methionine). The methionine source was dosed to deliver 6 grams of metabolizable methionine daily. Heifers received the treatments from day 90 to 180 of gestation, and all heifers were pair-feed during early- and late-gestation. Heifers’ plasma samples were collected on day 180 of gestation. Data were analyzed using mixed models. The model for plasma samples included the fixed effect of treatment and the random effect of block, while the birth weight model included the fixed effect of treatment, sex, and its interaction and the random effect of block. Plasma concentrations of insulin, glucose, and urea were not affected by treatments (P ≥ 0.20). Dietary supply of methionine increased plasma concentration of methionine (P < 0.01), and decreased glycine and serine (P < 0.01). None of the other essential and non-essential amino acids were affected by treatments (P ≥ 0.12). Heifers supplemented with methionine had a greater plasma concentration of the antioxidant taurine than control heifers (P = 0.04). A treatment × sex interaction was observed for calf birth weight; methionine-fed heifers delivered heavier male calves than control-fed heifers (P = 0.03). No treatment or sex effect was observed for calf birth weight (P ≥ 0.18). Our preliminary results indicate that methionine supply during mid-gestation affects fetal growth in beef cattle in a sex-dependent manner.