The potential of a phyllosilicate (Palabora vermiculite) as buffer in dairy cattle diets.

Four rumen-fistulated Holstein cows were used to determine the ability of vermiculite to alter rumen fermentation, rumen fluid dilution rate, milk production, and nutrient utilization in a 4 x 4 Latin square experiment. Treatments consisted of 1) basal diet (70% concentrate:30% Eragrostis curvula hay), 2) basal + .6% NaHCO3 + 1.8% vermiculite, 3) basal + 1.2% NaHCO3, and 4) basal + 3.6% vermiculite. Feed intake and milk production were not affected, but the NaHCO3 treatments tended to increase milk fat production. The 1.2% NaHCO3 treatment increased rumen pH and fluid dilution rate, decreased molar percent propionate, and increased acetate:propionate ratio. Rumen NH3 N was not affected. Milk yield (kg/d) and milk fat (%) for the treatments were 1) 19.3, 3.33; 2) 19.4, 3.59; 3) 19.8, 3.62; and 4) 18.7, 3.32. Rumen fluid pH, dilution rate (%/h), and acetate:propionate ratio were 1) 5.75, 10.9, 2.08; 2) 5.89, 11.5, 2.16; 3) 5.95, 12.1, 2.38; and 4) 5.80, 11.6 and 1.82. Treatments had little effect on nutrient digestibilities and serum mineral concentrations. Vermiculite did not show any promise as a buffer but NaHCO3 proved to be an effective buffer in diets based on Eragrostis hay and 70% concentrate diets.