PSV-9 Heat stress during gestation and post-weaning impact the performance of Bos indicus-influenced beef heifers.

Abstract This 2-yr study evaluated the effects of access to artificial shade during gestation and post-weaning (2 × 2 factorial design) on performance of Bos indicus-influenced beef heifers. On day 0 of each year (mid-August; 92 ± 20 d prepartum), 176 multiparous, pregnant Brangus cows were stratified by body condition score and body weight (BW) 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 day 330 (weaning; July). On day 330, 4 heifers per pasture were randomly selected (64 heifers per year) and then were transferred to 16 bahiagrass pastures (1 ha per pasture), using the same previous gestational pasture distribution. Post-weaning treatments were randomly assigned to pastures within each gestational treatment, in a 2 × 2 factorial arrangement (4 pastures per treatment combination), and consisted of heifers provided (SH) or not (NSH) access to artificial shade (4.5 m2 per heifer) from day 330 to 620 (pregnancy diagnosis). Heifers received concentrate DM supplementation (1.5% of BW) from day 330 to 620. Heifers were assigned to estrus synchronization from day 471 to 482, artificial insemination (AI) from day 483 to 485, and natural breeding by Angus bulls from day 495 to 585. Interactions among year, gestation, and post-weaning treatments were not detected (P ≥ 0.23) for any variable described herein. Gestational treatments: Heifers born from NSH cows had greater (P = 0.01) average daily gain (ADG) from day 330 to 373 compared to heifers born from SH cows, whereas overall ADG and percentage of mature BW at breeding did not differ (P ≥ 0.71) between gestational treatments; Heifers born from NSH cows had (P ≤ 0.01) reduced percentage of heifers detected in estrus (28 vs. 49 ± 7%) and conception percentage to AI (26 vs. 53 ± 7%) but similar final pregnancy percentage (80 vs. 83 ± 5%) compared with heifers born from SH cows. Post-weaning treatments: Heifers provided no post-weaning access to shade had less (P = 0.01) ADG from day 330 to 373 but greater (P = 0.04) ADG from day 373 to 482, leading to similar (P ≥ 0.39) overall ADG and percentage of mature BW at breeding compared with SH heifers; post-weaning treatment did not (P ≥ 0.39) impact any heifer reproductive variable. Hence, removing access to artificial shade during gestation or post-weaning had fluctuating impacts on heifer post-weaning growth, leading to similar heifer BW at breeding. However, removing access to shade during gestation (but not during post-weaning) compromised heifer reproductive performance as yearlings.