101 Effects of Live Yeast Supplementation on Complete Blood Cell Count and Febrile Responses in Heifers after Viral-Bacterial Respiratory Challenge.

Abstract

Experiment objectives were to determine if live yeast (LY) supplementation would impact immune and febrile responses to a viral-bacterial (VB) respiratory challenge. Thirty-eight crossbred Angus heifers (230 ± 16.4 kg) were allocated within a 2X2 factorial arrangement: Factor 1= roughage-based diet with or without LY (Saccharomyces cerevisiae boulardii I-1079, 62.5 gr/hd/d), Factor 2= VB, intranasal administration of bovine herpesvirus-1 (BHV-1, 2x108, PFU) and broncho-selective endoscopic inoculation with Mannheimia haemolytica (MH, 5.4x1010, CFU) 3 d post or intranasal saline administration followed by inoculation with phosphate buffer solution (PBS). Treatment arrangements were housed in separate pens (2 pens / treatment) and group-fed in electronic feedbunks. Heifers were randomized by MH and BHV-1 titer status, and fed their respective diets for 27 d prior to VB challenge on d 0. Thermo-boluses (Medria) measured rumen temperature (RUT) at 5-min intervals and rectal temperature (RT) was measured on d 0, 3–8, 10, 13 and 15. Whole blood samples were collected via venipuncture on d -13, -6, 0, 3–8, 10, 13 and 15 for complete blood count analysis. Data were analyzed using repeated measures in the mixed procedure of SAS with fixed effects of day, diet, VB challenge and their interactions. Animals fed LY exhibited a 16% increase (P=0.02) in neutrophils relative to controls. There were no other differences due to dietary treatment or interactions with day or VB challenge. There was a significant 3-way interaction for monocytes, which peaked on d 4 for VB treatment. LY supplementation increased (P<0.05) the level of monocytes relative to the control, suggesting a greater innate immune response. Viral-bacterial challenge produced nasal lesions that increased with d (P<0.01), reaching a nadir on d 6 with 70% of the naris covered with plaques, and increased (P<0.05) neutrophils on d 3–5 relative to PBS. Viral-bacterial challenge increased RUT (P<0.05) on d 2–7, but decreased RUT on d 9–12 relative to PBS. Rectal temperature was greater for VB heifers (P<0.05) on d 0, 3–6 and RT of PBS heifers never exceeded 40 C. The increase in RT on d 0 was most likely due to increased ambient temperature at time of challenge, as VB heifers were processed after the PBS heifers to avoid contamination. The VB challenge was effective at stimulating immune responses, and RUT was more sensitive than RT for measuring febrile responses. These results indicate that prior LY supplementation altered the leukogram in response to VB challenge, suggestive of increased innate immune response.