Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/1996
Publication Date: N/A
Interpretive Summary: Much of the protein eaten by ruminant farm animals (cattle, sheep, goats) is wastefully degraded to ammonia in the rumen. When cows were fed alfalfa hay and timothy hay in different proportions, the feed additive, monensin, decreased losses due to ammonia production and increased the amount of microbial protein and total volatile fatty acids that were produced. Microbial protein is a good source of protein for ruminant animals and volatile fatty acids are utilized as an energy source. Based on these results, monensin: 1) decreased ruminal amino acid degradation, 2) enhanced ruminal carbohydrate fermentation, and 3) provided the forage-fed ruminant with a better balance of fermentation end-products. This information will be useful in improving the efficiency of meat and milk production by ruminant farm animals.
Technical Abstract: When fistulated cows (n=2) were fed forage diets 12 times per day (9 kg DM per day), the rumen reached a steady state. The alfalfa hay had 1.39 times more crude protein and 1.41 times less NDF than the timothy, and the substitution of timothy for alfalfa caused an increase (P < .01) in ruminal ammonia concentration and total VFA. Alfalfa caused a small decrease (P < .01) in the ratio of ruminal acetate to propionate. The alfalfa had 1.46 times more potassium than timothy hay, but ruminal potassium concentrations were not affected (P > .05). At all combinations of timothy and alfalfa, monensin caused an increase (P < .05) in total VFA and the concentration of microbial protein in ruminal fluid. Because the increase in acetate was less than the increase in propionate, the ratio of acetate to propionate decreased (P < .05). Monensin decreased (P < .001) the specific activity of the mixed ruminal bacteria to produce ammonia from protein hydrolyzate in vitro at all combinations of alfalfa and timothy hay. Monensin decreased total ruminal ammonia when timothy was high, but decreased ruminal pH caused an increase in total ammonia when the proportion of alfalfa was high. Based on the pH and the pKa of ammonia, monensin caused a decrease in dissociated ammonia (NH3) at all but the highest proportion of alfalfa. Monensin caused an increase (P < .001) in ruminal potassium concentrations, but it had no effect (P > .05) on the potassium content of ruminal bacteria. Based on these results, monensin has the ability to decrease ruminal protein degradation and enhance the carbohydrate fermentation of forage-fed ruminants.