Effects of barley silage particle size and concentrate level on rumen kinetic parameters and fermentation patterns in steers

Soita, H. W., Christensen, D. A. and McKinnon, J. J. 2003. Effects of barley silage particle size and concentrate level on rumen kinetic parameters and fermentation patterns in steers. Can. J. Anim. Sci. 83: 533-539. Four Hereford steers (471 +- 31 kg) fitted with ruminal cannulae were used in a 4x4 Latin square design to evaluate the effects and possible interactions between silage particle size and concentrate level on digestion and ruminal fermentation parameters. Diets were designed with two forage to concentrate ratios [low forage, 20:80, high forage, 50:50 on a dry matter (DM) basis], combined with two theoretical chop lengths of barley silage; short (SBS) = 4.7 mm and long (LBS) =18.8 mm. Results showed that steers fed diets with SBS consumed more DM than those fed LBS. An interaction (P < 0.05) between particle size and concentrate level was noted for molar proportion of acetate. At the higher concentrate level, feeding SBS diets reduced the molar proportion of acetate but increased the molar proportion of propionate. An interaction (P < 0.05) between particle size and concentrate level was noted for ruminal pH. When compared to LBS, the daily mean rumen pH was lower (P < 0.05) for steers fed SBS with 80 % concentrate but not for those fed the 50% concentrate diet. Ruminal ammonia concentration was higher (P < 0.05) for those steers fed the 50% concentrate diets than for those fed the 80% concentrate diets. With high concentrate levels, SBS greatly reduced (P < 0.05) ammonia concentration. Passage rates for particulate matter and the retention time were decreased (P < 0.05) when SBS was fed. Feeding SBS reduced (P < 0.05) total tract digestibility of dry matter, crude protein (CP) and neutral detergent fiber (NDF) (65.5 vs. 68.5%, 66.5 vs. 73.4% and 39.4 vs. 45.9%), respectively. These results suggest that barley silage with a theoretical cut length of 18.8 mm can promote higher rumen pH, ammonia nitrogen, and reduced particulate passage rates. These changes in rumen fermentation parameters should favor optimum rumen function and digestion when high concentrate diets are fed.