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Effect of High Levels of Urea in Purified Diets for Lambs: Growth and Metabolism¹

Purdue University, Lafayette, Indiana 47907

Abstract

TWO experiments were conducted to determine the optimum level of dietary urea in a purified diet for lambs. Experiment I consisted of a 62-day growth study and a nitrogen balance study with wether lambs. Experiments 2 consisted of a 62-day growth study and a metabolism study with induced cryptorchid ram (I.C.R.) lambs. Weight gains, feed and water consumptions, terminal plasma urea, plasma free amino acids, N-balance and digestible energy were measured. The diets studied were: (R-14) 31% glucose, 22% corn starch, 25% cellulose, 10.75% isolated soy protein, 1.66% urea, 3% corn oil, 6.59% minerals and vitamins; (U-14) R-14 diet, 5% urea, soy protein deleted; (U-19) U-14 diet, 6.75% urea; and (U-24) U-14 diet, 8.5% urea. Dietary crude protein equivalents (C.P.) were 14, 14, 19 and 24%, respectively.

In Experiments 1, as the level of urea increased in the urea treatment diets, weight gains, feed consumptions, water intakes and terminal plasma urea levels increased linearly (P<.05). Wethers fed diets U-19 absorbed and retained more nitrogen than those fed diet U-14 (P<.05) in the nitrogen balance study which did not include the U-24 treatment diet.

In Experiment 2, there was a quadratic effect (P<.05) on weight gains and feed consumption as the level of urea increased in the urea treatment diets. I.C.R. lambs fed diet U-19 made the largest weight gains and consumed the most feed. As the level of urea increased in the diet, plasma urea levels increased linearly (P<.01). As the level of urea increased in the urea treatment diets, there was a quadratic effect (P<.10) on feed intakes. Nitrogen retentions were not affected by treatment in the metabolism study. However, when nitrogen retention values were adjusted to gross energy intakes, there was a linear increase (P<.10) in nitrogen retained as the level of dietary urea increased.

No definite amino acid patterns could be related to the urea treatments.

¹ Contribution from Department of Animal Sciences Journal Paper No. 4179.

² Present Address: VM 110, Bureau of Veterinary Medicine, F.D.A., 5600 Fishers Lane, Rockville, Md. 20852.

³ Present Address: University of South, Bahia Blanca, Argentina.