310 Effects of Stair Step Strategy and Immunomodulatory Feed Ingredient Supplementation on Thermoregulation, Growth, and Reproduction of Grazing Bos Indicus-Influenced Beef Heifers

Abstract

Abstract This 2-yr study evaluated the combination of stair step supplementation strategy and OmniGen-AF inclusion on body thermoregulation, growth, and reproduction of Bos indicus-influenced beef heifers. Brangus heifers (n = 64/year) were stratified by BW and age (257 ± 20 kg; 271 ± 22 d) and allocated into 16 bahiagrass pastures. Treatments were randomly assigned to pastures in a 2×2 factorial arrangement. Treatments consisted of concentrate dry matter (DM) supplementation at 1.50% of BW from day 0 to 100 (CON) or concentrate DM supplementation at 1.05% of BW from day 0 to 49 and 1.95% of BW from day 50 to 100 (SST), which included or not OmniGen-AF from day 0 to 100 (OMN; 4 g/45 kg of BW). Heifers were submitted to an estrus synchronization protocol from day 100 to 114, inseminated from day 112 to 114, and exposed to bulls from day 120 to 210. Data were analyzed using SAS GLIMMIX procedure. Heifer BW did not differ (P ≥ 0.49) on days 0 and 56, but on days 100 and 210 it was greater (P ≤ 0.01) for SST vs. CON. Intravaginal temperatures from day 26 to 30, between 0830 and 1600h were least (P ≤ 0.03) for SST offered OMN and did not differ (P ≥ 0.17) among all remaining treatments. Body surface temperature on day 25 and plasma IGF-1 concentrations on day 75 were greater (P ≤ 0.04) for SST vs. CON. Percentage of pubertal heifers, estrus detection, and pregnancy to AI did not differ (P = 0.36) between SST and CON, but final pregnancy percentage was greater (P = 0.04) for SST. Thus, OMN decreased intravaginal temperature of SST heifers but failed to improve their growth and reproduction, whereas the stair step strategy improved body thermoregulation, growth, and final pregnancy percentage of Bos indicus-influenced beef heifers.