Effects of monensin on chemical and physical aspects of digestion and nitrogen utilization in the ruminant

Abstract

A series of in vitro and in vivo trials were conducted to evaluate the effects of monensin on chemical and physical aspects of digestion and nitrogen utilization in the ruminant. In vitro trials 1 and 2 were conducted to test monensin's effects on free ammonia and free amino acid concentrations in fermentations containing four protein sources. In vitro trial 3 was conducted to test the effects of animal adaptation and monensin incorporation into substrate on free ammonia, free amino acids, dry matter disappearance and pattern of volatile fatty acids. A fourth in vitro trial was conducted to determine monensin's effect on deamination and proteolysis. Results of in vitro trials indicated that monensin increased the concentration of free amino acids where substrates were formulated with ingredients from plant sources. Monensin depressed free amino acid concentrations in fermentations containing casein. Few statistical differences were observed in in vitro trial 3. Poor fermentation in this trial indicated that microorganisms may have been shocked. Three in vivo trials were conducted utilizing Hereford, Angus and Hereford x Angus steers weighing 250 - 350 kg and fitted with permanent rumen and abomasal cannulae. Apparent digestibilities of the proximate components were determined as well as site of digestion of dry matter and nitrogen, rate of passage through the rumen and total tract and concentrations of ruminal volatile fatty acids, free ammonia and free amino acids. Monensin had no effect on rate of passage through the gastrointestinal tract or on apparent digestion of crude fiber, dry matter, nitrogen or ash. Steers consuming monensin supplemented diets digested more (P<.10) crude fat and nitrogen free extract, exhibited lower (P<.05) ruminal free amino acid concentrations, had less (P<.10) bacterial nitrogen passing the abomasum per day, retained less (P<.05) nitrogen when expressed as a percentage of nitrogen absorbed and appeared to digest less nitrogen in the rumen...