Effects of milk diets containing beef tallow or coconut oil on the fatty acid metabolism of liver slices from preruminant calves

Abstract

Coconut oil (CO) induces a triacylglycerol infiltration in the hepatocytes of preruminant calves when given as the sole source of fat in the milk diet over a long-term period. Metabolic pathways potentially involved in this hepatic triacylglycerol accumulation were studied by in vitro methods on liver slices from preruminant Holstein × Friesian male calves fed a conventional milk diet containing CO (n 5) or beef tallow (BT, n 5) for 19 d. Liver slices were incubated for 12 h in the presence of 0·8 mM-[14C] oleate or -[14C] laurate added to the medium. Fatty acid oxidation was determined by measuring the production of CO2 (total oxidation) and acid-soluble products (partial oxidation). Production of CO2 was 1·7–3·6-fold lower (P 0·0490) and production of acid-soluble products tended to be lower (P = 0·0625) in liver slices of CO- than BT-fed calves. Fatty acid esterification as neutral lipids was 2·6– to 3·1–fold higher (P = 0·0088) in liver slices prepared from calves fed the CO diet compared with calves fed the BT diet. By contrast with what occurs in the liver of rats fed CO, the increase in neutral lipid production did not stimulate VLDL secretion by the hepatocytes of calves fed with CO, leading to a triacylglycerol accumulation in the cytosol. It could be explained by the reduction of fatty acid oxidation favouring esterification in the form of triacylglycerols, in association with a limited availability of triacylglycerols and/or apolipoprotein B for VLDL packaging and subsequent secretion.