Removing maternal heat stress abatement during gestation modulated postnatal physiology and improved performance of Bos indicus-influenced beef offspring.

This study evaluated the growth and immune response of beef calves born from Bos indicus-influenced beef heifers provided pre- and post-partum heat abatement on pasture. At 83 ± 4 d prepartum (day 0), 64 Brangus crossbred beef heifers (~¼ Bos indicus) were stratified by body weight (BW; 454 ± 37 kg) and body condition score (BCS; 6.3 ± 0.28; scale 1 to 9), and then allocated into 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 (4.5 m 2 of shade area/heifer) from 83 d prepartum to 50 d post-partum (day 0 to 133). Heifers and calves were managed similarly from day 133 until the start of the breeding season (day 203). Calves were weaned on day 203 (at 119 ± 19 d of age), limit-fed the same drylot diet at 3.5% of BW (DM basis) day 209 to 268 (3 to 4 calves/pen; 8 pens/treatment) and vaccinated against respiratory disease pathogens on days 222 and 236. Heifer intravaginal temperatures from day 35 to 42 were lower (P ≤ 0.03) for NSH vs. SH heifers from 0000 to 0800 h but greater (P ≤ 0.05) for NSH vs. SH heifers from 1100 to 1800 h. Heifer intravaginal temperature from day 126 to 132 did not differ (P = 0.99) between NSH and SH heifers. Heifers assigned to NSH had greater respiration rates from day 20 to 96 (P ≤ 0.0007), greater plasma concentration of cortisol on days 35 (P = 0.07) and 55 (P = 0.02), less plasma concentration of insulin-like growth factor 1 (IGF-1) on day 35 (P = 0.10), 55 and 133 (P ≤ 0.05), and less BCS from day 55 to 203 (P ≤ 0.01) compared to SH heifers. Calves born from NSH heifers had less birth BW (P = 0.05), greater overall plasma haptoglobin concentrations (P = 0.05), greater seroconversion against bovine respiratory syncytial virus on day 222 (P = 0.02), tended to have greater ADG from day 209 to 268 (P = 0.07), and had greater BW on day 268 (P = 0.05) compared to SH offspring. Plasma concentrations of cortisol and serum titers against other respiratory disease pathogens did not differ (P ≥ 0.15) between NSH and SH offspring. Hence, removing maternal access to artificial shade: (1) increased prepartum intravaginal temperature and plasma concentrations of cortisol but reduced prepartum BCS and plasma concentrations of IGF-1 in grazing Bos indicus-influenced beef heifers; and (2) increased post-weaning BW gain and had positive effects on humoral immune response of their offspring.