Immune and Metabolic Responses of Beef Heifers Supplemented with to a Combined Viral-bacterial Respiratory Disease Challenge

Two treatments were evaluated in heifers to determine the effects of a yeast supplement on immune and metabolic responses to a combined (tandem viral-bacterial) respiratory disease challenge. Thirty-two beef heifers (325 ± 20.1 kg BW) were selected from a larger population previously assigned to one of two treatments: Control (CON), receiving no yeast supplement in the diet, or yeast (YST), CON diet plus a combination live yeast (2.5 g·heifer·d) and yeast cell wall (2.5 g·heifer·d) supplement (Phileo Lesaffre Animal Care, Milwaukee, WI). Heifers were maintained on treatments for 31 d prior to the challenge. On day -3 all heifers were fitted with an indwelling vaginal temperature recording device, received an intranasal challenge with 2 × 10 plaque-forming units of bovine herpesvirus-1 (BHV-1), and placed in outdoor pens. On day 0, all heifers were fitted with an indwelling jugular catheter, challenged intratracheally with an average dose of 3.0 × 10 colony-forming units (cfu) of in 100 mL media, and were transferred into individual stanchions in an enclosed, environmentally controlled barn. Whole blood samples were collected at -72 h and at 0, 2, 4, 6, 8, 12, 24, 36, 48, 60, and 72 h (hematology) and at 0, 1, 2, 3, 4, 5, 6, 7, 8, 12, 24, 36, 48, 60, and 72 h (serum isolation) relative to challenge (0 h). Data were analyzed using the MIXED procedure of SAS specific for repeated measures with fixed effects of treatment, time, and the treatment × time interaction. Vaginal temperature and cortisol concentrations were similar between treatments ( ≥ 0.39). Although total leukocyte count following BHV-1 challenge was similar between treatments ( = 0.21), there was a tendency ( = 0.07) for CON heifers to have greater neutrophil counts than YST heifers. Serum haptoglobin concentration was similar between treatments ( 0.13). Heifers in the YST treatment had similar serum glucose concentrations ( = 0.25) and decreased serum concentrations of urea nitrogen compared to CON ( = 0.03). Dietary treatment did not affect serum nonesterified fatty acid concentrations ( = 0.37). Nasal lesion score severity (0-4) tended ( = 0.07) to be decreased in YST compared to CON (2.5 vs. 3.19 ± 0.26), while water intake tended to be increased in YST ( = 0.06). Feeding a yeast supplement had little effect on the acute-phase response but improved metabolic outcomes in heifers during a respiratory disease challenge.