Yeast supplementation altered the metabolic response to a combined viral-bacterial challenge in feedlot heifers

Abstract Text: Two treatments were evaluated in feedlot heifers to determine the effects of feeding a yeast supplement on metabolic responses to a combined viral-bacterial respiratory disease challenge. Thirty-two beef heifers (325 ± 19.2 kg) were selected and randomly assigned to one of two treatments: 1) Control (CON), receiving a standard feedlot ration with no yeast supplement, or 2) yeast, (YEAST) control ration plus a combination live yeast (2.5 g·hd^-1·d^-1) and yeast cell wall (2.5 g·hd^-1·d^-1) supplement (Phileo-Lesaffre Animal Care, Milwaukee, WI). Cattle were maintained on treatments for 31 d. On d -3 all cattle were challenged intra-nasally with 1x10⁸ PFU of bovine herpesvirus-1 (BHV-1) and then allowed to rest in outdoor pens for 3 d. On d 0, each heifer was challenged intra-tracheally with approximately 3x10⁷ CFU of Mannheimia haemolytica, was fitted with an indwelling jugular catheter and indwelling vaginal temperature recording device, and was moved into individual stanchions in an environmentally-controlled barn. Whole blood samples were collected at the time of BHV-1 challenge, at 1-h (serum) or 2-h (complete blood cell counts) intervals from 0 to 8 h, and at 12, 24, 36, 48, 60, and 72 h following the M. haemolytica challenge. Data were analyzed using the mixed procedure of SAS specific for repeated measures with fixed effects of treatment, time, and their interaction. Cattle in the YEAST group had a greater glucose concentration following M. haemolytica challenge (121.38 ± 2.91 vs. 109.86 ± 2.90 mg/dL, respectively; P < 0.01) and decreased serum concentrations of blood urea nitrogen compared to CON (11.82 ±0.53 vs. 10.12 ± 0.53 mg/dL, respectively; P = 0.03). There was no difference in serum NEFA concentration between YEAST (0.14 ± 0.01 mg/dL) and CON (0.15 ± 0.01mg/dL; P= 0.37). These data indicate that feeding a combination live yeast and yeast cell wall product may modulate energy stores by reducing muscle catabolism to provide energy for the activated immune system in response to a respiratory disease challenge. The reduction in catabolism has the potential to improve live animal performance when an animal is exposed to respiratory diseases.

Keywords: feedlot health, respiratory disease challenge, yeast