Utilization of urea by sheep

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Abstract
1.The breakdown of urea, soluble starch and glucose was followed in the rumen of fistulated sheep and in artificial rumens containing rumen ingesta or strained rumen fluid.2. Carbohydrate remained in the rumen two to three times as long when starch was dosed in vivo as when glucose was given.3. The relative rates of breakdown of urea and carbohydrate by strained rumen fluid in vitro differed markedly from those in vivo. This was due to the fact that straining removed large numbers of starch- and glucose-utilizing micro-organisms which were attached to the larger food particles, while the concentration of the urea-splitting organisms which were freely suspended in the strained liquor was apparently the same as that obtained in the strained material. Strained rumen fluid should therefore not be used for studies of the utilization of urea in vitro.