315 Inadequate body condition at calving negatively affects perinatal nutrient availability in beef calves.

Abstract Fall-calving beef females in the Fescue Belt face challenges of poor nutrient availability, heat stress, and fescue toxicosis during late pregnancy, all of which can contribute to poor body condition score (BCS) at calving. Our objective was to use dam and calf data from studies in which females did not undergo planned nutrient restriction to investigate effects of poor peripartum BCS on calf perinatal nutrient availability. Prepartum dam body weight (BW), calf size and vigor at birth, expelled placenta size, single rear-quarter colostrum yield, dam prepartum and postpartum (1 h) circulating metabolites, and neonatal calf metabolites (0, 6, 12, 24, and 48 h of age) were combined from 6 fall-calving experiments. Dams were assigned to a peripartum BCS category of Adequate (5 to 6.5, 5.6 ± 0.4; n = 170) or Inadequate (< 5, 4.5 ± 0.3; n = 78). Mixed linear models (experiment as a random effect, calf sex in the model if P < 0.25) were used to determine effects of BCS category. Calf metabolites over time were analyzed with fixed effects of BCS category, hour, and their interaction, using repeated measures. Dams with inadequate BCS were younger (3.4 vs. 4.3 ± 0.6; P = 0.001) and weighed less (570 vs. 647 ± 21; P < 0.001) than those with adequate BCS. Calves born to inadequate BCS dams weighed less (31.6 vs. 33.1 ± 1.1; P = 0.02), had smaller heart and flank girths (P ≤ 0.02), and tended to have smaller abdominal girth (P = 0.10), but weighed more as a percent of dam prepartum BW (P = 0.001). Gestation length of AI-sired calves and calf time to stand (indicator of vigor) were not affected (P ≥ 0.53) by BCS category. Dry whole placenta, cotyledonary, and intercotyledonary weights were less (P ≤ 0.02) for calves born to inadequate BCS dams, but placental efficiency (kg calf/g placenta) was not affected (P = 0.36). Dams with inadequate BCS had less (P = 0.02) single rear-quarter colostrum yield with less (P = 0.03) total immunoglobulin G. Pre-calving circulating triglycerides were less (P = 0.02) and non-esterified fatty acids (NEFA) tended to be less (P = 0.07) for inadequate BCS dams. Additionally, inadequate BCS dams had less (P ≤ 0.009) circulating glucose and NEFA, but greater (P < 0.001) urea N post-calving. Neonatal calf circulating glucose and triglycerides were affected by (P ≤ 0.02) BCS category x hour. Calves born to inadequate BCS dams had less (P ≤ 0.05) glucose at 6, 12, 24, and 48 h, along with less (P ≤ 0.05) triglycerides at 12, 24, and 48 h. These data demonstrate that fall-calving beef females with BCS < 5 at calving likely compromise perinatal nutrient availability for their calves.