PSIX-39 Supplementing an immunomodulatory feed ingredient to improve thermoregulation and performance in finishing beef cattle under heat stress conditions

Abstract

Abstract This experiment compared physiological and productive parameters in finishing cattle managed under heat stress conditions, and supplemented or not with Omnigen-AF (Phibro Animal Health, Teaneck, NJ). Crossbred cattle (Bos taurus × B. indicus; 64 heifers and 64 steers) were ranked by initial body weight (BW; 440 ± 3 kg) and sex, and allocated to 1 of 16 pens (8 heifers or steers/pen). Pens within sex were randomly assigned to receive (OMN; n = 8) or not (CON; n = 8) Omnigen-AF at 56 g/cow daily (as-fed basis). Cattle received a total-mixed ration during the experimental period (d 0 to 107), and Omnigen-AF was offered daily as a top-dress to OMN. Cattle were shipped on d 107 to a commercial packing facility for slaughter. Cattle BW was recorded and samples of blood and tail-switch hair collected on d 0, 28, 56, 84, and 106. Feed intake was evaluated biweekly from each pen, and feed efficiency calculated according to total feed intake and BW gain of each pen. From d 0 to 7, 28 to 42, and 84 to 98, heifer intravaginal temperature was recorded hourly (iButton temperature loggers DS1922L, Maxim Integrated, San Jose, CA). Environmental temperature humidity index (THI) was also recorded hourly throughout the experiment, and averaged 79.8 ± 0.6. Heifers receiving OMN had less (P < 0.05) vaginal temperature from 1500 to 1900h (39.05 vs. 39.19 °C), when THI ranged from 85.3 to 90.1. No treatment effects were detected (P > 0.20) for BW gain, feed intake, feed efficiency, and carcass traits. No treatment effects were also detected (P > 0.17) for plasma concentrations of cortisol and haptoglobin, and cortisol concentrations in tail-switch hair. Hence, OMN ameliorated hyperthermia in finishing cattle exposed to heat stress conditions, but such benefit was not sufficient to improve productive and physiological responses.