Journal of Animal Science, Vol 73, Issue 12 3775-3784, Copyright © 1995 by American Society of Animal Science

CLINICAL TRIAL

In vitro ouabain-sensitive respiration and protein synthesis in rumen epithelial papillae of Hereford steers fed either timothy hay or timothy hay supplemented with cracked corn once daily

J. M. Kelly, A. S. Vaage, L. P. Milligan and B. W. McBride
Department of Animal and Poultry Science, University of Guelph, ON, Canada.

Rumen epithelial papillae samples, acquired from the Central sac of six adult Hereford steers (585 +/- 17 kg) fed either timothy hay plus soybean meal (T) or timothy hay plus cracked corn and soybean meal (TC) once daily (0900), were used in a crossover design to study the daily pattern of O2 consumption and protein synthesis. Tissue samples were acquired at 0900, 1200, 1800, and 2400 over a 10-d sampling period. Additionally, ruminal fermentation characteristics (pH, ammonia, VFA, and osmolality) were measured at 0430, 0900, 1030, 1200, 1500, 1800, 2100 and 2400. Total, ouabain-insensitive (OIO2), and cycloheximide-insensitive (CIO2) O2 consumption were greatest at 2400 (P < .01, P < .06, and P < .02 respectively). Additionally, steer fed TC had a greater CIO2 at 2400. In conjunction with a temporal effect on ruminal fermentation patterns, after an initial decline, there was an increase (P < .05) in total O2, ouabain-sensitive (OSO2), OIO2, and CIO2 consumption throughout the day. Fractional rates of protein synthesis were not different at any time point between diets. Rumen epithelial metabolism exhibits a temporal pattern in cattle fed once daily.