The clearance rate of rumen liquid and rumen fermentation pattern in sheep receiving forage diets

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Abstract
SUMMARY: An experiment was carried out to study the composition of the mixture of rumen short-chain fatty acids and the clearance rate of the rumen liquid phase in sheep given diets of dried grass, high-nitrogen hay, low-nitrogen hay and barley straw. Differences between diets in clearance rate were not significant (P > 0·05) and differences between diets in the composition of the mixture of rumen acids were small. There were substantial variations in clearance rate between individual sheep but this was not associated with variations in the pattern of fermentation and the correlation between the proportion of propionic acid and the clearance rate in the rumen was low (r = –0·23).In a second experiment sheep receiving a moderate-quality hay were given intravenous injections of atropine sulphate which resulted in significant increases in rumen volume (P < 0·01) and significant reductions in ruminal clearance rate (P < 0·05). These were accompanied by significant increases in the numbers of protozoa (P < 0·05) and bacteria (P < 0·05) in the rumen but the composition of the mixture of rumen short-chain fatty acids was unchanged.It is concluded that there is little possibility through alteration of ruminal clearance rate, for manipulation of rumen fermentation pattern in sheep receiving diets of moderate- or poor-quality forages.