Effect of a Combination of Live Yeast and Yeast Cell Wall Products Supplemented before and after Weaning on Immune Function in Heifer Calves

Ninety-five heifer calves (initial BW = 165 ± 27 kg) were used to evaluate the effects of live yeast and yeast cell wall products fed prior to weaning and through a backgrounding period on immune function. Heifer calves were stratified based on BW, birthdate, sire, and dam parity; and were assigned randomly to pasture (10 pastures, 9 or 10 cow-calf pairs/pasture). Pastures were assigned randomly to 1 of 2 treatments; 1) no yeast (CON), or 2) the addition of yeast product (YP). Calves were offered a 5% salt limiting creep-feed (47.5% cracked corn and 47.5% DDG) at 0.5% of BW for 35 d prior to weaning. The YP creep-feed was formulated to provide 4 g YP/d (3 g of live yeast, and 1 g of yeast cell wall product; Phileo Lesaffre Animal Care, Milwaukee, WI). Heifers offered YP consumed an average of 3.2 g/d of the YP through the creep-feeding period. After weaning, heifers remained in their pre-weaning groups and were fed 1.8 kg/d of a grain supplement for 42 d; YP provided 4 g of YP/d. Blood was collected for serum haptoglobin concentration and complete blood cell analyses on d -1, 35 (weaning), 49, and 76. Blood collected on d 35 and 76 was analyzed by flow cytometry to determine phagocytic activity (pHrodo™ BioParticles® Phagocytosis Kit, Thermo Fisher Scientific, Waltham, MA). Data were analyzed using the MIXED procedure in SAS with day as the repeated measure; main effects of treatment and day were analyzed and the subsequent interaction of treatment x day. Significance was declared at P ≤ 0.05. A treatment effect (P = 0.32) was not observed for white blood cell concentration between CON and YP. Furthermore, there was no difference (P = 0.13) in the neutrophil to lymphocyte ratio. However, there was an effect of day (P < 0.01) on the neutrophil to lymphocyte ratio with d 49 being the greatest, followed by weaning (d 35), d 76, and -1. Serum haptoglobin concentrations were not affected (P = 0.15) by the addition of YP in the diet; however, there was a day effect (P < 0.01) on serum haptoglobin concentrations. Furthermore, the percentages of cells that were positive for phagocytic activity were not different (P = 0.97) between treatments. In summary, the supplementation of YP pre- and post-weaning had no effect on the measures of immunocompetence that were evaluated in these heifers.