Measurement of the Adaptation Response to Urea-Nitrogen Utilization in the Ruminant

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Abstract
Observations from 63 lambs receiving a high-urea, semipurified ration employed in 19 digestion and metabolism trials were subjected to multiple regression analysis in order to measure independently the effect of adaptation to urea feeding and the effects of changes in ration composition. The retention of absorbed nitrogen was significantly improved by approximately two percentage units with each consecutive 10-day feeding period up to 50 days, with no measurable change in the digestibility of organic matter or crude fiber. Increasing the percentage of total nitrogen supplied as urea from 54 to 68% significantly depressed the retention of absorbed nitrogen to the extent of approximately 12 percentage units; had no significant effect upon the digestibility of organic matter; and significantly depressed the digestibility of crude fiber by approximately 8 percentage units. Increasing the total nitrogen content of the ration from 1.5 to 2.0% had no significant effect upon the retention of absorbed nitrogen, but significantly decreased the digestibility of organic matter and crude fiber. Increasing the crude fiber content of the ration from 20 to 26% had no significant effect upon the digestibility of organic matter, but significantly improved the digestibility of crude fiber by approximately 10 percentage units.