Effect of Propionic Acid on Kinetics of Acetate and Oleate and on Plasma and Milk Fatty Acid Composition of Goats

Abstract

Entry rates of acetate and oleate and their incorporation into lipids of blood plasma and fatty acids of milk were studied in lactating goats fed a concentrate-roughage ration with propionic acid infused intraruminally at 0, 5.52, and 13.74 g/h.by primed constant intravenous infusion of [l-carbon-14] acetate and [9, 10-hydrogen-3] oleate. Means for infusion rates were acetate, 60, 52, and 39 μg/ml blood plasma; propionate 9, 12, and 22 μg/ml; oleate, 19, 14, and 12 μg/ml; acetate entry rate, 3.9, 2.7, and 1.8 mmol/h per kg bodyweight; oleate entry rate, 47, 29, and 19 μmol/h per kg bodyweight; acetate oxidation rate, 2.0, 1.7, and 1.4 mmol/h per kg, and its contribution to the total carbon dioxide production, 16, 14, and 11%. Propionic acid increased incorporation of carbon-14 and hydrogen-3 into plasma lipids, elevated proportions of 7:0, 9:0, 11:0, 13:0, 15:0, and 17:0 fatty acids in milk, and tended to lower others. Specific radioactivities of milk fatty acids during infusion of propionic acid were elevated by 1.8 to 2.8 times, and total fatty acids in milk and plasma were lowered by 22 and 38%. Data support the glucogenic theory that propionic acid either directly or through gluconeogenesis stimulates insulin secretion, which in turn inhibits release of fatty acids from adipose tissue, resulting in milk fat depression. © 1984, American Dairy Science Association. All rights reserved.