Journal of Animal Science, Vol 75, Issue 4 1100-1111, Copyright © 1997 by American Society of Animal Science

JOURNAL ARTICLE

Ardacin for steers grazing endophyte-free fescue pasture: effects on live weight gain, forage intake, nitrogen and fiber digestion, ruminal fluid kinetics, ruminal fermentation, and serum hormones and metabolites

M. B. Judkins, D. W. Holcombe, B. W. Hess, L. J. Krysl, M. A. Branine and J. D. Hess
School of Veterinary Medicine, University of Nevada, Reno 89557-0104, USA.

Growth and digestion studies were conducted to evaluate the use of ardacin as a feedgrade antibiotic for enhancing digestive function and growth in grazing steers. In Exp. 1, 90 yearling steers (average initial BW of 248 kg) used in a randomized complete block design (block = weight group) grazed fescue pasture without supplementation (CON) or with daily supplements (DM basis) of .4% of BW supplemental ground corn (CRN) or .4% of BW supplemental corn supplying 120 mg of ardacin (ARD). In Exp. 2, 12 ruminally and duodenally cannulated steers and three ruminally cannulated steers (Hereford x Angus; average BW of 347 kg) were used to evaluate the effects of the same supplements used in Exp. 1 on ruminal fermentation and digestion. In Exp. 1, ARD-supplemented steers weighed more (P < .01) at the conclusion of the study than CRN steers, which together weighed more (P < .01) than CON steers. Average daily gain was greater (P < .10) in supplemented than in CON steers; ARD steers had greater (P < .01) ADG than CRN steers. In Exp. 2, forage intake and harvesting efficiency did not vary (P > .10) with supplementation or type of supplement, but total intake reflected (P = .03) the addition of corn to the forage diet. Addition of ardacin increased (P = .02) ruminal pH compared with CRN steers. Ardacin decreased ruminal molar proportions of acetate and increased (P = .01) propionate proportions when compared with CRN steers. Total tract N digestibility was affected (P < .10) by supplementation and by addition of ardacin to the diet. Addition of ardacin to the ground corn supplement increased ADG, in part by enhancing acetate:propionate ratios and increasing N digestion.

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