Effects of feeding synthetic zeolite A and sodium bicarbonate on milk production, nutrient digestion, and rate of digesta passage in dairy cows.

Four rumen-cannulated Holstein cows were fed synthetic zeolite A and NaHCO3 to evaluate their affect on milk production, nutrient digestibility, rumen fermentation, and rate of digesta passage. Treatments were allocated in a 2 x 2 factorial arrangement within a 4 x 4 Latin-square design. Treatments consisted of control; 1.0% NaHCO3; 2.0% zeolite; and 1.0% NaHCO3 plus 2.0% zeolite. A total mixed ration with 50:50 concentrate to forage (80% corn silage, 20% haylage) DM was fed. Intake of DM was lower for cows receiving zeolite (18.7 vs. 20.7 kg/d). Decreases were noted in daily milk (26.3 vs. 28.9 kg/d). 4% FCM (23.6 vs. 25.6 kg/d); milk fat yield (.86 vs. .93 kg/d); milk protein yield (.85 vs. .95 kg/d); and milk protein percent (3.21 vs. 3.34) with zeolite. Digestibilities of DM, organic matter, and crude protein were also decreased by zeolite but ADF digestion was unaffected. Rumen pH was increased, ruminal propionate decreased, and acetate:propionate ratio increased by zeolite. All other VFA plus rumen NH3 were not affected by treatment. Decreases due to zeolite were observed in liquid fractional rate of passage and liquid flow rate when measured by Cr-EDTA in the feces. No treatment differences were found in fractional rate of passage of feed particles. Addition of NaHCO3 had no significant effects.