Effect of a Hydrolyzed Mannan and Glucan Rich Yeast Fraction on Performance and Health Status of Newly received Feedlot Cattle.

: A two-part experiment was conducted to determine the effects of a blend of specialized mannan rich and glucan rich fractions of yeast (Select-TC, Alltech Inc.) on the health status and performance of steers during the first two months of the feedlot period. Eighty crossbred steers were acquired from commercial sale barns in Mississippi and Georgia, and transported to Purdue University. All animals were fed a corn silage based receiving diet, and were checked and treated daily for respiratory disease as needed following established treatment protocols. In Exp. 1, 64 steers (246.5 ± 4.7 kg initial weight) were blocked by body weight (BW) and randomly allocated to 2 treatments to determine the impact of supplementation of a hydrolyzed mannan and glucan rich yeast fraction for 56 d on BW, average daily gain (ADG), daily dry matter intake (DMI), and gain:feed: hydrolyzed yeast fed at 13 g (as-fed)/steer daily (TC) or non-supplemented control (CON). Steers in Exp. 1 were housed in bedded pens with 2 animals/pen (n = 16 pens [32 steers]/treatment). In Exp. 2, 16 steers (247.1 ± 5.4 kg initial BW) were similarly allotted to two treatments (CON and TC), individually penned, and subjected to a lipopolysaccharide (LPS) endotoxin challenge on d 62 or 63 after the start of the study to determine the animal's response to an inflammatory agent. Serum samples and rectal temperatures were taken every half an hour from -2 to 8 h relative to LPS injection from steers in Exp. 2. Data were analyzed as a complete randomized block design using the MIXED procedure of SAS. Morbidity for both experiments did not differ (P ≥ 0.16). Weight, ADG, DMI and gain:feed, did not differ among treatments (P ≥ 0.32) in Exp. 1. After the LPS infusion in Exp. 2, rectal temperatures (P = 0.03) and serum non-esterified fatty acid (NEFA) concentration (P = 0.04) were decreased in TC compared to CON steers. Concentrations of blood urea nitrogen (P = 0.31), glucose (P = 0.70), insulin (P = 0.57) and cortisol (P = 0.77) did not differ by treatment after LPS administration. Serum interleukin-6 concentrations were decreased (P < 0.0001) and interferon-γ concentrations tended to be greater (P = 0.07) in TC compared to CON steers after LPS infusion. Serum cytokine and metabolite results indicate that Select TC improved health and metabolic status of LPS-challenged cattle, but this did not result in quantifiable improvements in performance in the conditions observed in this study.