Monensin Effects on Diet Digestibility, Ruminal Protein Bypass and Microbial Protein Synthesis

Abstract

The influence of monensin on diet digestibility, microbial protein synthesis and ruminal bypass of dietary plant protein was evaluated in two lamb trials and a steer trial. Lamb trial I determined monensin effects on diet digestibility, rumen and blood parameters when two sources of supplemental nitrogen, brewers dried grains (BDG) or urea, were fed. Dry matter digestibility (DMD) and nitrogen retention were reduced by monensin regardless of supplemental nitrogen source (P<.05). Nitrogen digestibility was not altered. Ruminal acetate: propionate ratios, protozoal populations and ammonia (NH₃) levels were reduced (P<.05) and plasma urea levels increased (P<.05) by monensin addition. Lamb trial II was conducted similar to the first trial except that total collections of feces and urine were made on days 11 to 17 and again on days 40 to 46 of the trial. Monensin addition reduced acetate: propionate ratios (P<.05). Rumen NH₃ levels and protozoal populations were reduced and plasma urea levels increased by monensin addition, similar to trial I results. Dry matter and acid detergent fiber (ADF) digestibilities were significantly reduced by monensin, especially at the 38 ppm level. By days 40 to 46 these parameters approached those of the control indicating a possible adaptation effect. The steer trial used abomasally cannulated animals to evaluate monensin effects on nitrogen fractions entering the small intestine when fed with BDG or urea as the supplemental nitrogen source. Monensin addition decreased bacterial nitrogen and increased plant nitrogen flow on both the BDG and urea supplemented diets. Abomasal essential and nonessential amino acid flow was greater on BDG supplemented diets than on urea supplemented diets. Monensin addition increased amino acid flow on BDG diets but not urea diets. These studies indicate monensin may spare dietary protein by decreasing ruminal proteolysis. Monensin may also reduce urea utilization since flow of bacterial nitrogen was significantly reduced. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.