Yeast supplementation alters the performance and health of cattle during the receiving period
The objective of this experiment was to determine the effect of yeast supplements on performance and health of steers during the receiving period. Weaned crossbred steers (n = 184; initial BW = 203 ± 1 kg) were blocked by BW and randomly assigned to pen (4 pens/block; 5-6 hd/pen). Pens within a block were randomly assigned to one of four treatments (9 pens/treatment): 1) control (CON; no yeast additive), 2) live yeast (LY; 5 g.hd-1.d-1 BIOSAF, Lesaffre Feed Additives, Milwaukee, WI), 3) yeast cell wall (YCW; 5 g.hd-1.d-1 Pronady 500, Lesaffre Feed Additives), 4) live yeast + yeast cell wall (LY+YCW; 5 g.hd-1.d-1 live yeast and 5 g.hd-1.d-1 yeast cell wall). Daily DMI was recorded and individual BW was collected every 14 d for 56 d. Data were analyzed using a randomized complete block design using the fixed effect of treatment and random effect of block (SAS Inst. Inc., Cary, NC). A subset of 24 steers was utilized after 38 d on feed to determine the effect of yeast supplementation on the response to a lipopolysaccharide (LPS) challenge. Calves were fitted with jugular catheters and indwelling rectal temperature measuring devices that measured rectal temperature at 1-min intervals, and were moved into individual stanchions. On d 39, blood samples were collected at 30-min intervals from -2 to 8 h and then at 24 h relative to administration of LPS (0.5 μg/kg BW) at 0 h. Blood samples were used to determine serum interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), cortisol concentrations, and neutrophil:lymphocyte (N:L) ratios. Data were subjected to analysis of variance specific for repeated measures using Statview (SAS Inst. Inc.) with sources of variation including treatment, time and their interactions. Specific time point comparisons within treatment group were conducted using a Paired t-test to compare pre-challenge values with specific time points post-challenge. Steers receiving LY or YCW showed a 7% numerical increase (P = 0.59) in ADG and a 7.7 ± 4.7 kg increase in BW at d 56. Cumulative DMI increased (P = 0.05) for the LY, YCW, and LY+YCW treatments compared to CON (5.47, 6.02, 5.96, and 5.89 kg/d; CON, LY, YCW, and LY+YCW, respectively). Steer morbidity and mortality were not affected by yeast supplementation (P ≥ 0.10). In response to LPS challenge, basal RT prior to LPS tended (P ≤ 0.06) to differ among groups with CON calves having higher RT compared to LY+YCW (P ≤ 0.01) and LY (P ≤ 0.04) calves. After the LPS challenge, RT remained higher in the CON calves compared to other treatments (P ≤ 0.05). By 10 h post-LPS, RT were still greater (P ≤ 0.05) in CON calves compared to all other calves, and remained numerically greater throughout the study. Serum cortisol increased in all groups post-LPS with peak concentrations observed at 1 h. Peak cortisol concentrations were 26.5 ng/mL greater (P ≤ 0.04) in CON calves compared to LY+YCW calves. Interferon-gamma (IFN-γ) concentrations tended (P ≤ 0.06) to be greater in CON calves compared to YCW calves prior to LPS exposure. Collectively, these data indicated that the use of yeast additives increased total feed consumed by the steers during the first 56 d of the feeding period, and improved health, thus allowing for enhanced performance.