Level of Readily Fermentable Carbohydrates and Adaptation of Lambs to All-Urea Supplemented Rations

Digestion and nitrogen metabolism data obtained with 83 lambs fed semipurified rations containing urea as the sole source of supplemental nitrogen were used to estimate the influence of length of time of urea feeding and level of readily fermentable carbohydrates on the retention of absorbed nitrogen. Regression analysis indicated that the retention of absorbed nitrogen by lambs was significantly improved by 3 percentage units with each 10-day period of urea feeding. The retention of absorbed nitrogen was significantly improved by approximately 2 percentage units for each 100 kcal of readily fermentable carbohydrates in the rations of lambs. Improvement in the retention of absorbed nitrogen due to the level of readily fermentable carbohydrates was observed in lambs regardless of the degree of their adaptation to urea feeding. The digestion of crude fiber was significantly decreased by 8 percentage units for each 1000 kcal of readily fermentable carbohydrates in the ration.