Supplementing an immunomodulatory feed ingredient to improve thermoregulation and performance of finishing beef cattle under heat stress conditions

Abstract

This experiment compared physiological and productive responses in finishing beef cattle managed under heat stress conditions, and supplemented (SUPP) or not (CON) with an immunomodulatory feed ingredient (Omnigen-AF; Phibro Animal Health, Teaneck, NJ). Crossbred yearling cattle (¾ Bos taurus × ¼ Bos indicus; 64 heifers and 64 steers) were ranked by initial body weight (BW) (440 ± 3 kg) and sex, and allocated to 1 of 16 unshaded drylot pens (8 heifers or steers/pen). Pens within sex were randomly assigned to receive SUPP or CON (n = 8/treatment). Cattle received a total-mixed ration (91% concentrate inclusion and 1.21 Mcal/kg of net energy for gain; dry matter [DM basis]) during the experiment (day 0 to 106). The immunomodulatory feed was offered as a top-dress to SUPP pens (56 g/d per animal; as-fed basis) beginning on day 7. Cattle BW were recorded on day 0, 14, 28, 42, 56, 70, 84, 98, and 106. Feed intake was evaluated from each pen by recording feed offer daily and refusals biweekly. Intravaginal temperature of heifers was recorded hourly from day 1 to 6, 29 to 41, and 85 to 97. Environmental temperature humidity index (THI) was also recorded hourly throughout the experiment, and averaged 79.8 ± 0.6. Concurrently with BW assessment, hair samples from the tail-switch were collected (3 animals/pen) for analysis of hair cortisol concentrations. Blood samples were collected on day 0, 28, 56, 84, and 106 from all animals for plasma extraction. Whole blood was collected on day 0, 56, and 106 (3 animals/pen) for analysis of heat shock protein (HSP) 70 and HSP72 mRNA expression. Cattle were slaughtered on day 107 at a commercial packing facility. Results obtained prior to day 7 served as independent covariate for each respective analysis. Heifers receiving SUPP had less (P ≤ 0.05) vaginal temperature from 1500 to 1900 h across sampling days (treatment × hour, P < 0.01; 39.05 vs. 39.19 °C, respectively; SEM = 0.04), when THI ranged from 85.3 to 90.1. Expression of HSP70 and HSP72 was less (P ≥ 0.03) for SUPP cattle on day 106 (22.6- vs. 51.5-fold effect for HSP70, SEM = 9.7, and 11.0- vs. 32.8-fold effect for HSP72; treatment × day, P ≤ 0.04). No treatment effects were detected (P ≥ 0.22) for performance, carcass traits, plasma concentrations of cortisol and haptoglobin, or hair cortisol concentrations. Results from this study suggest that SUPP ameliorated hyperthermia in finishing cattle exposed to heat stress conditions, but such benefit was not sufficient to improve productive responses.

Keywords: feedlot cattle; heat stress; immunomodulation; performance; temperature.

Figure 1.

Environmental THI (Willard et al., 2003) and vaginal temperature of feedlot cattle supplemented with an immunomodulatory feed ingredient (SUPP; n = 8) or not (CON; n = 8) during a 106-d finishing period. Values were recorded hourly (day 1 to 6, day 29 to 41, and day 85 to 97 of the experiment) using intravaginal thermometers (iButton temperature loggers DS1922L, Maxim Integrated, San Jose, CA) or an hygrochron temperature/humidity logger (iButton temperature loggers DS1923-F5, Maxim Integrated). Treatments were provided from day 7 to 106; hence, results from day 1 to 6 were averaged and included as independent covariate in each analysis. Treatment × day (panel A) and treatment × hour (panel B) interactions were detected (P ≤ 0.01). Values reported are covariately adjusted means. Within day or hour; * = P ≤ 0.05, † = P ≤ 0.10.

Figure 2.

Body weight of feedlot cattle supplemented with an immunomodulatory feed ingredient (SUPP; n = 8) or not (CON; n = 8) during a 106-d finishing period. Values were recorded prior to the first feeding of the day. Growth rate of each animal was modeled by linear regression of body weight against sampling days, and each regression coefficient was used as individual response. No treatment differences (P ≥ 0.27) in growth rate (1.23 vs. 1.20 kg/day for CON and SUPP, respectively; SEM = 0.02) or body weight were noted.