Acute immunological responses to a combined viral-bacterial respiratory disease challenge in feedlot heifers supplemented with yeast

Abstract Text:

Two treatments were evaluated in commercial feedlot heifers to determine the effects of a yeast supplement on immune responses to a combined viral-bacterial respiratory challenge. Thirty-two beef heifers (325 ± 19.2 kg BW) were selected and randomly assigned to one of two treatments, and fed for 31 d: 1) Control (CON), receiving a standard feedlot ration without a 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). All cattle were challenged intra-nasally with 1x10⁸ PFU bovine herpesvirus-1 (BHV-1) on d -3 and then allowed to rest in outdoor pens for 3 d. On study d 0, each animal was challenged intra-tracheally with an average dose of 3x10⁷ CFU Mannheimia haemolytica, was fitted with an indwelling jugular catheter and an 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 relative to 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. Water intake per hour tended (P = 0.06) to be greater in the YEAST group compared to CON. Nasal lesion scores tended (P = 0.07) to be decreased in the YEAST group compared to CON (2.50 ± 0.26 vs. 3.19 ± 0.26, respectively). There was no difference in cortisol concentrations or vaginal temperature between treatment groups (P ≥ 0.37). There was no treatment difference (P = 0.21) in total white blood cell counts following BHV-1 challenge. There was a trend (P = 0.13) for serum haptoglobin concentration to be reduced in the YEAST (11,757.3 ± 1631.7 μg/dL) group compared to CON (15,396.174 ± 1631.7 μg/dL). Cattle in the CON group tended (P = 0.07) to have greater neutrophils than YEAST (6.39 ± 0.39 vs. 5.37 ± 0.37 K/μL, respectively). In summary, feeding a combination live yeast and cell wall yeast supplement tended to reduce nasal lesion score, inflammatory response, and neutrophil count with no effect on febrile response in beef heifers. Further research is warranted to determine if other measures of the inflammatory response were influenced by yeast supplementation in this model of respiratory disease challenge.

Keywords: feedlot health, respiratory disease challenge, yeast