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Caloric Value of Acetate and Propionate for Lactating Dairy Cows^1,2,

Department of Animal Sciences, New Hampshire Agricultural Experiment Station, Durham 03824

ABSTRACT

Two mature Holstein cows with rumen fistulas were fed hay, corn silage, and concentrate in a fixed ratio (air-dry basis) of 5:15:20 and in quantity intended to minimize tissue energy change. Acetate (A) or propionate (P) or an equicaloric mixture (M) of A and P, prepared by partially neutralizing (pH 4.4) respective acids with NaOH, was diluted, and infused (19 liters daily) into the rumen continuously for 9 days to supply about 10% of ration metabolizable energy; dry feed allowance was reduced accordingly. A water (control) infusion preceded each of three series of treatments (A, M, and P randomly arranged), and all data were expressed as deviations from the series control. The experiment was a randomized complete block design with six cow-series combinations as blocks.

Volatile fatty acid infusions produced expected effects on volatile fatty acids and blood ketones without affecting rumen pH or blood buffer capacity. Acid treatments, particularly propionate, reduced total gross energy intake slightly without differentially affecting energy, dry matter, or proximate nutrient digestibility. Acetate exerted a positive and propionate a negative influence on milk fat and energy content. Efficiency of conversion of metabolizable energy to milk was not different among treatments. Relative differences in volatile fatty acid utilization in the fasting cow and sheep apparently cannot be extrapolated to predict the influence of various diets on milk production in the cow.

¹ Published with the approval of the Director of the New Hampshire Agricultural Station as Scientific Contribution 614.

² Technical assistance of H. H. Hayes is gratefully acknowledged.