Mammary extraction of propionate in lactating cows

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 that the control diet. Concomitant changes in acetate, beta-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 beta-hydroxybutyrate also were correlated negatively, evidence of a direct inhibitory effect of propionate in mammary gland is equivocal.