44 Impacts of Pre- and Postpartum Heat Stress Abatement on Physiology and Performance of GrazingBos Indicus -Influenced Cow-Calf Pairs

Abstract This study evaluated the impacts of heat abatement during pre- and postpartum periods on physiology and performance of beef heifers and their calves. On day 0, 64 Brangus beef heifers (21 mo of age) were stratified by their initial body weight (BW; 454 ± 37 kg) and body condition score (BCS; 6.3 ± 0.28) and then were allocated into of 1 of 16 bahiagrass pastures (1 ha and 4 heifers/pasture). Treatments were randomly assigned to pastures (8 pastures/treatment) and consisted of heifers provided (SH) or not (NSH) access to artificial shade from day 0 to 33 (83 ± 4 d prepartum until 50 ± 4 d postpartum). Shade structures were removed on day 33. Calves were weaned on day 203 (119 ± 9 d of age), and then transferred to 1 of 16 drylot pens (3 to 4 calves/pen) and limit-fed a soybean hulls-based diet (3.25% of BW) until day 268. Data were analyzed as a complete randomized design using MIXED and GLIMMIX procedures for non-binary and binary variables, respectively. Heifer BCS on days 55, 133 and 203 were greater (P ≤ 0.01) for SH vs. NSH heifers. Plasma glucose did not differ (P ≥ 0.29), whereas plasma IGF-1 were greater (P ≤ 0.05) on days 55 and 133 for SH vs. NSH heifers. Calf BW was less (P = 0.05) for NSH vs. SH calves at birth, did not differ (P = 0.44) at weaning, and was less (P = 0.05) for SH vs. NSH calves on day 268. Plasma haptoglobin concentrations were greater (P = 0.05) and serum titers against bovine respiratory syncytial virus tended (P = 0.10) to be less for SH vs. NSH calves after vaccination. Serum titers against all remaining viruses did not differ (P ≥ 0.24) between treatments. Therefore, heat abatement during pre- and postpartum increased heifer BCS and plasma IGF-1 during late-gestation, increased calf birth BW, reduced calf post-weaning growth, and had minor changes to calf humoral immune function.