Mammary Extraction of Propionate in Lactating Cows

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Abstract
Cows (4) with exteriorized carotid arteries were in an intensive study of concentrations in plasma and mammary extraction of propionate [PRP]. 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, .beta.-hydroxybutyrate, and glucose in plasma and in fat and protein in milk were measured. Mammary arteriovenous difference in PRP was correlated negatively with milk fat percentage. Since arterial PRP and .beta.-hydroxybutyrate also were correlated negatively, evidence of a direct PRP inhibitory effect in mammary gland is equivocal.