Milk production, nutrient digestion, and rate of digesta passage in dairy cows fed long or chopped alfalfa hay supplemented with sodium bicarbonate

Effects of forage particle size and sodium bicarbonate on milk production, ruminal fermentation, ruminal fluid dilution rate, dry matter passage from the rumen, and nutrient digestion were measured in four Holstein cows in a 4 X 4 Latin-square experiment. Cows were fed ad libitum amounts of a diet of approximately 46% concentrate and 54% alfalfa hay. The 2 X 2 factorial arrangement of treatments were: 1) long stem alfalfa hay, 2) long stem alfalfa hay + 1.4% sodium bicarbonate (3.0% of concentrate), 3) chopped alfalfa hay (1.3 cm), and 4) chopped alfalfa hay + 1.4% sodium bicarbonate. Feed intake, milk yield, and milk composition were similar among treatments. Ruminal pH and concentration and molar percentages of volatile fatty acids were not altered. Decreasing feed particle size reduced ruminal fluid outflow as estimated by polyethylene glycol and chromium ethylenediamine tetraacetic acid dilution rates. Digestion of nutrients was decreased with chopped alfalfa hay but was not related to faster rate of passage of smaller size feed particles as determined by rare earth markers. Sodium bicarbonate increased water intake and tended to improve nutrient digestion. Absence of a significant effect of sodium bicarbonate upon rate of passage of chopped hay indicates that feed particles of this size are not significantly affected by small increases of dilution rate of ruminal fluid. Addition of sodium bicarbonate to an alfalfa hay (forage)-based diet did not improve production responses but did increase nutrient digestion.