Influence of forage Species and Level of Intake on Ruminal Turnover Rates

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Abstract
Rumen fistulated wether lambs were used in a 4 x 4 Latin square design to investigate the effects of forage species and level of feed intake on rumen liquid and solid turnover rates. Rumen fermentation measurements and digestibility coefficients were also determined. Two levels of intake and two forage species, alfalfa (A) and orchard grass (O), were compared. Ninety percent of the ad libitum intake of each sheep, as determined in a preliminary trial, was designated as the high (H) intake treatment while 60% of the H value was the low (L) intake treatment. Cobalt EDTA was used as the marker to measure liquid turnover while Yb-labelled hay was used as the solid phase marker. Apparent digestibility coefficients for organic matter, crude protein (CP) and acid and neutral detergent fiber were not affected (P>.05) by level of intake. Acid and neutral detergent fiber digestibilities were higher (P<.01) for sheep fed orchard grass than for those fed alfalfa hay. Digestibility of CP was greater (P<.01) for sheep fed alfalfa hay than those offered orchard grass. Volatile fatty acid concentrations (μmol/ml), pH, molar proportions of acetate and propionate and acetate: propionate ratios were not significantly changed by level of intake or forage species. Ammonia N concentrations weighted over time were 21.2, 22.6, 13.5 and 13.5 mg/100 ml for the HA, LA, HO and LO diets, respectively, with no apparent differences in rumen NH3-N level within species despite differences in amounts of dietary N consumed. There was approximately a twofold (.072 vs .033 h-1) increase (P<.025) in liquid turnover rate at the higher level of intake when averaged over forage species. Although at the higher level of intake there was a tendency for greater solids turnover rates (.066 and .053 h-1 for the H and L level intakes, respectively), no significant differences were observed for intake or forage species. Results of this study suggest that level of intake influences ruminal liquid turnover rate to a greater extent than it affects solid turnover rate. Ruminal fermentation patterns were similar within forage species regardless of intake or differences in liquid turnover rate of the digesta. Copyright © 1982. American Society of Animal Science . Copyright 1982 by American Society of Animal Science.

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