Milk Production, Nutrient Digestion, and Rate of Digesta Passage in Dairy Cows Fed Long or Chopped Alfalfa Hay Supplemented with Sodium Bicarbonate,

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Abstract
Effects of forage particle size and NaHCO3 on milk production, ruminal fermentation, ruminal fluid dilution rate, dry matter passage from the rumen and nutrient digestion were measured in 4 Holstein cows in a 4 .times. 4 Latin-square experiment. Cows were fed ad lib amounts of a diet of .apprx. 46% concentrate and 54% alfalfa hay. The 2 .times. 2 factorial arrangement of treatments were: long stem alfalfa hay, long stem alfalfa hay + 1.4% NaHCO3 (3.0% of concentrate), chopped alfalfa hay (1.3 cm) and chopped alfalfa hay + 1.4% NaHCO3. 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 CrEDTA 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. NaHCO3 increased water intake and tended to improve nutrient digestion. Absence of a significant effect of NaHCO3 upon rate of passage of chopped hay indicated that feed particles of this size were not significantly affected by small increases of dilution rate of ruminal fluid. Addition of NaHCO3 to an alfalfa hay (forage)-based diet did not improve production responses but did increase nutrient digestion.