Abstract
One hundred medium-framed, crossbred steers (738 lb) were used to compare nonprotein nitrogen to natural protein supplementation of finishing diets for implanted steers. Diets were formulate d to contain 11.5 or 13.5% crude protein and were supplemented with either urea or soybean meal. A fifth treatment of cottonseed meal supplementation (13.5% dietary crude protein) was added to evaluate differences between natural sources of rumen degradable protein. Steers were implanted with Revalor® and fed for 132 days. During the first 70 days, daily gain and feed efficiency were improved 8.8 and 6.1%, respectively, for steers supplemented with soybean meal vs urea. No difference was observed with protein level. For the entire feeding period, soybean meal increased dry matter intake 3.8% compared to urea. Protein source and level interacted on daily gain. Increasing dietary protein from 11.5 to 13.5% decreased gain by urea-fed steers 8%, whereas increasing dietary protein fr om 11.5 to 13.5% increased gain 6.1% for steers supplemented with soybean meal. Soybean meal improved feed efficiency 7.6% compared to urea. Protein level had no effect on feed efficiency. Steers supplemented with soybean meal had larger loineye areas than those supplemented with urea. Carcass finish, percentage of carcasses grading Choice, and yield grade were not affected by treatment . Performance and carcass traits of steers fed cottonseed meal were similar to those of steers fed soybean meal. We conclude that urea cannot meet the metabolizable protein needs of implanted finishing steers. Cottonseed meal did not differ from soybean meal as a protein source in this study.
Highlights
Growth promotants, especially the combination of estradiol and trenbolone acetate, have the potential to alter nutrient requirements in feedlot steers
During the first 70 days, daily gain and feed efficiency were improved 8.8 and 6.1%, respectively, for steers supplemented with soybean meal vs urea
Protein level had no effect on feed efficiency
Summary
Especially the combination of estradiol and trenbolone acetate, have the potential to alter nutrient requirements in feedlot steers. Current information concerning requirements of rapidly growing feedlot steers for rumen degradable and metabolizable protein is limited. Soybean meal and urea are two commonly used sources of protei n in finishing diets. The usefulness of urea is limited to the amount that provides sufficient rumen ammonia to maximize microbial protein production and(or) rumen organic matter digestion. Other research presented in this publication suggests that, urea supplementation increases rumen organic matter digestion, it does not enhance protein flow to the small intestine. Soybean meal contains a degradable protein fraction to supply ammonia, amino acids, peptides, or other growth factors to rumen microbes, as well as an escape fraction to increase true protein reaching the small intestine. Our objective was to evaluate two levels of soybean meal and urea on performance and carcass traits of implanted finishing steers
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