Abstract
To test the efficacy of rumen-protected lysine and methionine, six steers (486 lb) were used in a 6 4 incomplete Latin square design and fed corn-urea diets (85% concentrate) alone or supplemented with 2 or 4% soybean meal to give dietary crude protein levels of 12.5, 13.2, and 14.0% (as fed-basis). Each diet was fed with or without 5 g/day Smartamine-ML (rumen-protected lysine and methionine). Steers were fed to gain 2.6 lb/day. Nitrogen retention increased linearly, from 30.7 g/day (0% soy) to 35.5 g/day (4% soy) as the level of soybean meal and, thus, crude protein, increased in the diet. Supplementing steers with lysine had no effect on nitrogen retention. Total tract organic matter digestibility was similar for all treatments. No protein level lysine interaction occurred. We conclude that lysine was not the first limiting amino acid in the corn-urea soybean meal diets used in this study.
Highlights
Lysine often is identified as the amino acid most likely to be limiting in feedlot diets because cereal grains, especially corn, contain relatively low levels of lysine
To test the efficacy of rumen-protected lysine and methionine, six steers (486 lb) were used in a 6 4 incomplete Latin square design and fed corn-urea diets (85% concentrate) alone or supplemented with 2 or 4% soybean meal to give dietary crude protein levels of 12.5, 13.2, and 14.0%
From 30.7 g/day (0% soy) to 35.5 g/day (4% soy) as the level of soybean meal and, crude protein, increased in the diet
Summary
Lysine often is identified as the amino acid most likely to be limiting in feedlot diets because cereal grains, especially corn, contain relatively low levels of lysine. A dietary deficiency of an essential amino acid will cause cattle to use metabolizable protein less efficiently. Rumen-protected amino acids may afford the opportunity to correct amino acid deficiencies without having to increase the quantity of metabolizable protein. It may be possible to decrease protein levels while still maintaining current levels of performance. Our objectives were to investigate whether we could supplement steers with rumen-prote cted lysine to 1) increase steer nitrogen balance at a given level of dietary protein or 2) feed lower levels of crude protein without compromising performance
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