Effects of increasing levels of grain supplementation on rumen environmentand lactation performance of dairy cows grazing grass-legume pasture

The impact of supplemental energy on nutrient utilization, fiber digestion, rumen fermentation, and lactation performance was evaluated in dairy cows grazing pastures composed of brome, orchardgrass, red clover, and alfalfa. Three amounts [0, 5, and 10 kg dry matter (DM)/d] of ground dry shelled cor n-based concentrate were supplemented to nine rumen cannulated Holstein cow s in a 3 x 3 Latin square replicated three times. Cows were on average 84 /- 13 d in milk and producing 41.6 +/- 5.9 kg of milk/d at the beginning of the study. An increase in amounts of concentrate in the diets was associat ed with an increase in milk production, solids-corrected milk, and concentr ations of milk protein and SNF. Milk fat percentage and milk urea nitrogen concentration decreased linearly with supplementation. Milk production and protein percentage were 21.8, 26.8, and 30.4 kg/d, and 2.85, 2.95, and 3.05 % for the increasing levels of concentrate, respectively. Intake and digest ibility of DM and organic matter (OM) increased as grain supplementation in creased. Ruminal pH and total volatile fatty acid concentration (VFA) were not affected by supplementation or the amount of concentrate. Ruminal ammon ia concentration was reduced by supplementation, presumably due to a decrea se in N intake and greater use of ammonia-N for rumen microbial protein syn thesis. Rumen fermentation varied throughout the day, with lower mean pH an d higher VFA concentrations at night. Supplementation increased total OM in take, decreased forage OM intake, and increased the proportion of OM that w as digested in the intestines. Total DM, intake by grazing dairy cows can b e increased using ground dry shelled corn-based concentrate without causing negative effects on forage digestion.