Factors affecting the voluntary intake of food by cows. 3. The effect of urea on the voluntary intake of oat straw

Campling, R.C.; Freer, M.; Balch, C.C.

British Journal of Nutrition 16: 115-124


ISSN/ISBN: 0007-1145
PMID: 13876094
Accession: 014045411

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The effect of urea on the voluntary intake of oat straw by adult non-lactating cows was examined in a series of 4 experiments, each with 2 to 4 cows. The urea was given in solution, alone or with sucrose, as a continuous intraruminal infusion. The infusion of 75g or 150g urea/day caused a mean increase of about 40% in the voluntary intake of oat straw. The inclusion of 500g sucrose in the infusion caused no further increase in intake. A daily infusion of 25g urea caused an increase of only 26% in voluntary intake. The infusion of 150g urea/day increased the mean digestibility of the organic matter of the straw from 41 to 50%, owing entirely to increases in the digestibility of crude fiber and nitrogen-free extract of 11 and 9 percentage units respectively. The rate of disappearance of cotton threads suspended in the rumen of cows receiving urea was 6 to 7 times faster than in cows not receiving urea. When measured at controlled levels of straw intake, the mean retention time of food residues in the alimentary tract was decreased from 104 to 83 h during urea administration. Twenty-four hours after feeding began approximately equal amounts of digesta dry matter were found in the reticulo-rumens of cows offered straw ad lib. with or without the infusion of urea. These results are discussed in relation to the hypothesis that the voluntary intake of this roughage is related to its rate of disappearance from the reticulo-rumen.