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

In Bos taurus beef heifers, altering the timing of body weight (BW) growth pattern either reduced feed costs without decreasing reproduction or enhanced reproduction without increasing feed costs. Moreover, supplementation of OmniGen-AF (OMN, a patented immunomodulatory feed ingredient) decreased internal body temperature in dairy and beef B. taurus cattle, with variable impacts on growth and reproduction. Combining both nutritional strategies for Bos indicus-beef heifers developed under heat stress conditions of tropical and subtropical environments has not been reported in the literature yet and was the main objective of the present study. For 100 d before the breeding season, heifers received either a constant supplementation amount or stair-step (SST) supplementation strategy (50 d of low followed by 50 d of high supplement amount), with or without OMN inclusion. Overall, OMN supplementation alleviated the internal body temperature of heifers but did not improve their growth and reproduction, whereas the SST strategy increased BW gain and final pregnancy percentage of B. indicus-influenced beef heifers under heat stress conditions.