Effect of age and dietary fat level on fatty acid oxidation in the neonatal pig

A total of 35 pigs were obtained by cesarean section, placed in individual sterile isolators, and randomly allotted to treatment groups. Thirty pigs received purified, isoenergetic liquid diets containing 2 or 32% butterfat (dry matter basis) and were killed at 1, 7, or 21 days of age. Five pigs were killed at 2 hours post delivery and received no diet. Twenty-one-day old pigs showed a tendency for higher weight gain and feed consumption when consuming the 32% fat diet although the differences were not significant. The rate of oxidation of [U-14C]palmitate to CO2 and acid soluble products was measured in homogenates of liver, kidney, heart, and leg muscle (biceps femoris) from pigs 0, 1, 7, and 21 days of age. The relative rates of oxidation of [U-14C]myristate, [U-14C]palmitate, and [U-14C]stearate were measured in homogenates of liver from 7-day old pigs. Palmitate oxidation was stimulated by carnitine in all four tissues and the rate of carnitine-stimulated palmitate oxidation to acid soluble products in heart and to CO2 in liver was higher in tissues from pigs consuming the 32% fat diet. The rate of palmitate oxidation increased with age in liver, kidney and leg muscle tissues and was maximum at 21 days in kidney and leg muscle and at 7 days in liver. The rate of palmitate oxidation in heart tended to decrease with animal age. In homogenates of liver from 7-day old pigs, palmitate was oxidized at a faster rate than stearate or myristate. The activities of carnitine palmitoyltransferase (CPT) (EC 2.3.1a) and succinate dehydrogenase (EC 1.3.99.1) in mitochondria isolated from liver, kidney, heart, and leg muscle did not vary considerably with age although CPT activity tended to be higher in those tissues from pigs consuming the high fat diet. Changes in the rate of palmitate oxidation with age tended to parallel changes in the level of mitochondrial protein per g of wet tissue and suggested an increased ability to utilize fat as an energy substrate during early development of the neonatal pig.