RUMEN FERMENTATION AND NUTRIENT DIGESTION IN CATTLE FED DIETS VARYING IN FORAGE AND ENERGY-SOURCE

Four Holstein steers, each fitted with a rumen fistula and duodenal t-shaped cannula, were used in a 4 X 4 Latin square design to measure the rumen fermentation and digestibility of the following diets: (1) alfalfa hay and barley; (2) alfalfa hay and ground com; (3) corn silage and barley; (4) corn silage and corn. All diets contained 50% forage and 50% concentrate on a dry matter (DM) basis, with a minimum of 10% of the DM as alfalfa hay. Diets based on alfalfa hay had more organic matter digestion in the rumen and total digestive tract than those containing corn silage. Diets containing corn as the major concentrate energy source had less ruminal starch digestion and a greater flow of organic matter to the duodenum than diets containing barley. Total tract digestion of nitrogen (N) was greater for barley than com diets, but was similar between forage sources. Neither the forage nor concentrate energy source affected bacterial protein synthesis. Rumen pH was higher and ammonia-N was lower in alfalfa than barley diets. In addition, rumen acetate was higher and rumen propionate was lower, resulting in a greater acetate-to-propionate ratio in alfalfa diets.