Stair step strategy and immunomodulatory feed ingredient supplementation for grazing heat-stressed Bos indicus-influenced beef heifers

Authors: MORIEL, PHILIPE - University Of Florida; PALMER, ELIZABETH - University Of Florida; OLIVEIRA, RHAIZA - University Of Florida; VEDOVATTO, MARCELO - University Of Florida; IZQUIERDO, VINICIUS - University Of Florida; SILVA, HIRAN - University Of Florida; GARZON, JAIME - University Of Florida; Dailey, Jeffery; Carroll, Jeffery - Jeff Carroll; Sanchez, Nicole; MARTINS, THIAGO - University Of Florida; BINELLI, MARIO - University Of Florida; VENDRAMINI, JOAO - University Of Florida

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2022
Publication Date: 4/2/2022
Citation: Moriel, P., Palmer, E.A., Oliveira, R.A., Vedovatto, M., Izquierdo, V.S., Silva, H.M., Garzon, J., Dailey, J.W., Carroll, J.A., Sanchez, N.C., Martins, T., Binelli, M., Vendramini, J.M. 2022. Stair step strategy and immunomodulatory feed ingredient supplementation for grazing heat-stressed Bos indicus-influenced beef heifers. Journal of Animal Science. 100(4). https://doi.org/10.1093/jas/skac107.
DOI: https://doi.org/10.1093/jas/skac107

Interpretive Summary: Finding the best nutritional strategy for the development and fertility of replacement beef heifers is of significant interest to the beef cattle industry. While prior studies have evaluated the use of nutritional supplements during the development phase of heifers, none have evaluated these strategies in heat-tolerant heifers under topical/sub-tropical conditions. Therefore, scientists from the University of Florida and ARS' Livestock Issues Research Unit collaborated on a study to evaluate different supplementation strategies to improve development and fertility of heat-tolerant heifers during heat stress conditions. Results from this study indicated that stair stepping supplementation improved growth and reproductive performance of heat-stressed heifers compared to a constant supplementation strategy. Additionally the results demonstrate that the stair-step strategy is a viable heifer development strategy for tropical/subtropical environments. This information will be of interest to cattle producers in southern regions of U.S. with tropical/subtropical environments and to beef cattle nutritionist.

Technical Abstract: On day 0 of year 1 and 2, sixty-four Brangus crossbred heifers were stratified by initial body weight (BW) and age (mean = 257 ± 20 kg and 271 ± 22 d) and allocated into 16 bahiagrass pastures (4 heifers/pasture/yr). Treatments were randomly allotted to pastures in a 2 × 2 factorial arrangement of treatments (4 pastures/treatment/yr). 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 an immunomodulatory feed ingredient 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. Heifers detected in estrus from day 111 to 114 were submitted to artificial insemination (AI) 12 h after estrus detection. Heifers not detected in estrus were timed AI on day 114. All heifers were exposed to Angus bulls from day 120 to 210 (1 bull/pasture). Effects of supplementation strategy × OMN inclusion × hour were detected (P < 0.0001) only for intravaginal temperature from day 26 to 30, which were the least (P = 0.03) for SST heifers offered OMN supplementation and did not differ (P = 0.17) among all remaining treatments from 0830 to 1600 h. Effects of supplementation strategy × OMN inclusion and OMN inclusion were not detected (P = 0.12) for any variable, except for percentage of heifers detected in estrus, which was greater (P = 0.01) for heifers supplemented or not with OMN. Total concentrate DM offered from day 0 to 100 and heifer BW on days 0 and 56 did not differ (P = 0.49) between CON and SST heifers, but SST heifers were heavier (P = 0.01) on days 100 and 210 compared to CON heifers. Body surface temperature on day 25 and plasma IGF-1 concentrations on day 75 were greater (P = 0.04) for SST vs. CON heifers. Percentage of pubertal heifers, heifers detected in estrus, and pregnancy to AI did not differ (P = 0.36) between SST and CON heifers but final pregnancy percentage was greater (P = 0.04) for SST vs. CON heifers. Thus, OMN supplementation decreased intravaginal temperature of SST heifers but failed to improve their growth and reproduction, whereas the SST strategy improved body thermoregulation and growth and final pregnancy percentage of grazing heat stressed Bos indicus-influenced beef heifers compared to a constant concentrate supplementation strategy.