The effects of intravenous infusions of triglycerides on the secretion of milk fat in the cow

Abstract

1. Artificial emulsions of nine synthetic triglycerides ranging from tripropionin to triolein were given as continuous infusions into the jugular vein of lactating cows for periods of 2 days. The effects of these infusions on the composition of blood lipids and on the secretion of the component fatty acids in milk were examined.2. Tricaproin, tricaprylin, tripelargonin, tricaprin, trilaurin, trimyristin and triolein, in contrast to tripropionin and tributyrin, increased the yields in milk of the acid contained in the triglyceride. The increased yield of acid was positively correlated with chain length of the infused triglyceride, and with triglycerides above tricaprin the transfer of fatty acid to milk was sufficiently large to give consistently increased yields of total milk fat.3. The infusions increased the concentrations in blood plasma of cholesterol, phospholipid and in some experiments also of triglyceride. Concentrations of these lipids returned to normal by 2 days after the infusion. The fatty acid compositions of the plasma triglycerides were not affected by the infusion of triglycerides up to tripelargonin but with triglycerides longer than this the plasma triglycerides were altered in composition towards that of the infused triglyceride.4. Short- and intermediate-chain fatty acids of the infused triglycerides were elongated by the successive addition of two carbon units to give increased yields in milk of acids ranging up to C15and C16when they contained acids with an even and odd number of carbon atoms respectively. Possible interference with the conversion of stearic into oleic acid in the mammary gland owing to the infused emulsions is also discussed.