Mammary extraction of propionate in lactating cows.

Abstract Four cows with exteriorized carotid arteries were in an intensive study of concentrations in plasma and mammary extraction of propionate. A restricted-roughage, high-grain diet produced higher arterial propionate concentrations and larger carotid-subcutaneous abdominal vein (arteriovenous) differences than the control diet. Concomitant changes in acetate, β-hydroxybutyrate, and glucose in plasma and in fat and protein in milk were measured. Mammary arteriovenous difference in propionate was correlated negatively with milk fat percentage. However, since arterial propionate and β-hydroxybutyrate also were correlated negatively, evidence of a direct inhibitory effect of propionate in mammary gland is equivocal.