PS6-10. Effects of Heat Stress Mitigation During Late Gestation on Post-weaning Growth, Immunity, and Carcass Characteristics of Bos Indicus-influenced Steer Offspring.

Abstract This study evaluated the impacts of access to artificial shade during late gestation on post-weaning growth, immune response, and carcass traits of Bos indicus-influenced beef steers. On day 0 (92 ± 20 d prepartum), 176 multiparous, pregnant Brangus cows were stratified by body condition score and body weight and allocated into 16 bahiagrass (Paspalum notatum) pastures (8 ha and 11 cows per pasture). Gestational treatments were randomly assigned to pastures and consisted of cows provided (SH) or not (NSH) access to artificial shade (4.5 m2 per cow) from day 0 to 90. Cows and calves were managed similarly from calving to weaning (day 330). At weaning, 3 steers per pasture (n = 48 steers) were randomly selected and assigned to preconditioning (day 351 to 398) and feedlot periods (day 399 to 609). Steers were vaccinated for bovine respiratory diseases on days 351 and 370. All animals were managed similarly with no treatments applied during the preconditioning and feedlot periods. Steer non-binary and binary data were analyzed using the MIXED and GLIMMIX procedure of SAS, respectively. During the preconditioning period, steer growth performance did not differ (P ≥ 0.27) between treatments, but plasma cortisol concentration on day 353, plasma haptoglobin concentration on day 356, and plasma insulin-like growth factor 1 (IGF-1) concentration on day 398 were greater (P ≤ 0.05) for steers born from SH vs. NSH cows. Compared with steers born from NSH cows, steers born from SH cows had greater (P = 0.05) serum titers against parainfluenza 3 virus 19 days after vaccination (day 370) but reduced (P ≤ 0.02) seroconversion against bovine viral diarrhea virus type 1a before and 19 days after vaccination (days 351 and 370, respectively). Steer growth performance during the feedlot period did not differ (P ≥ 0.49) between treatments. Carcass traits did not differ between treatments (P ≥ 0.12), except that the proportion of carcasses grading Prime tended to be greater for steers born from SH vs. NSH cows (15 vs. 0.4 ± 5%; P = 0.06). In summary, providing access to shade for pregnant beef cows during late gestation did not impact post-weaning growth performance of their male offspring, but increased plasma IGF-1, cortisol, and haptoglobin, had minor changes to humoral immune response, and increased carcass quality of their offspring.