The feeding of urea supplements to sheep and cattle: the results of penned feeding and grazing experiments

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Abstract
1. A number of penned feeding and grazing experiments are described in which sheep and cattle, fed diets of low-quality roughage, were given supplements of urea and molasses, or urea and starch. 2. Starch was unsatisfactory as a source of supplementary carbohydrate, and it was concluded that this was mainly due to its low palatability. Molasses added without urea to a diet of straw for penned sheep increased intake and reduced the rate of live-weight loss in one experiment, but had no effect in another. 3. In general, supplementing low-quality rough-age with urea and molasses in both penned feeding and grazing experiments increased food intake and reduced the rate of live-weight loss. A supplement of urea alone increased food intake, but did not affect live-weight loss. The addition of ethanol or phosphoric acid to urea-molasses supplements had no additional beneficial effect. Supplementation with urea and molasses increased wool growth, but this increase was not always significant. 4. The general effect of urea on rumen contents was to increase pH, V.F.A. and ammonia N levels; the effect of molasses was to decrease pH and ammonia N levels, and increase V.F.A. levels. 5. Spraying of dry, standing herbage with urea and molasses increased the crude protein (N × 6·25) content, but this effect disappeared in 3–4 days. Sprayed herbage was markedly preferred by grazing animals, and generally one third of the sprayed herbage was removed within 24 hr. of spraying. 6. The advantages and disadvantages of the pasture-spraying technique, and the possibilities of other methods of feeding supplements containing urea to grazing animals, are discussed. 7. In no experiment where unsupplemented animals were losing weight did urea and molasses supplementation cause substantial increases in weight. It is concluded that the main value of supplementing low-quality roughage with urea and molasses would be for the survival, and possibly the maintenance, of animals.