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Effect of Monensin on Nitrogen Utilization and Digestibility of Concentrate Diet by Steers^1,2,

University of Arizona, Tucson 85721

Abstract

Monensin was fed at levels of 0 and 33 ppm in a series of digestion and metabolism trials to determine its effect on utilization of high grain diets and on ruminal parameters in yearling steers. Monensin had no effect (P>.05) on apparent digestibility of dry matter, gross energy or starch when fed with a 90% corn diet (10.5% crude protein, dry matter basis). Monensin in this corn-based diet tended to increase crude protein digestibility (63.4 vs 61.3%) and decrease ruminal ammonia concentration (2.5 vs 6.5 mg/100 ml) measured 3 hr post-prandially (P>.05). In metabolism trials with a 76% sorghum grain diet (11.7% crude protein, dry matter basis), monensin improved apparent digestibility of crude protein (P<.05) but not dry matter or gross energy (P>.05). Retention of nitrogen, expressed as a percentage of nitrogen intake, tended to improve (24 vs 20%) in response to monensin addition to the sorghum grain-based diet (P>.05); a similar trend was observed (P>.05) for nitrogen retention expressed as a percentage of nitrogen absorbed (41 vs 36%). Total ruminal volatile fatty acid (VFA) concentrations measured 3 hr post-prandially were not altered by monensin fed with either diet. The proportion of acetic acid decreased (P<.05) and that of propionic acid increased (P<.05) in response to monensin fed with the corn-based diet. Monensin did not appreciably alter proportions of VFA when fed with the sorhgum grain-based diet. Results suggest that a possible improvement in N utilization may account for some of the benefits of feeding monensin with high grain diets.

¹ Arizona Agr. Exp. Sta. Tech. Paper No. 2952. Appreciative acknowledgement is extended to Dr. Robert O. Kuehl for advice and assistance in the statistical analyses.

² This paper is part of a dissertation prepared by the senior author in partial fullfullment of requirements for the Ph.D. degree in Agr. Biochem. and Nutr.