Effect of dietary medium chain triacylglycerols on plasma triacylglycerol levels in horses

The hypothesis tested was that the feeding of medium chain triacylglycerols (MCT) to horses would raise the level of plasma triacylglycerols by increasing the availability of glucose as lipogenic substrate, implying that the MCT effect would be greater with glucose in the diet instead of cellulose. A Latin square experiment was carried out with 4 horses and 4 dietary treatments. The experimental periods lasted 21 d. Blood samples were taken 16 h after feeding. The diets consisted of hay and experimental concentrates, differing in fat source (MCT or soybean oil) and carbohydrate source (corn starch plus glucose or cellulose). The dietary variables, MCT or soybean oil, provided on average 27% of total dietary net energy, while glucose plus cornstarch or cellulose provided 33%. The feeding of MCT versus soybean oil raised the level of plasma triacylglycerols significantly from 196.7 ± 30.2 to 427.3 ± 85.7 mmol/1 and that of VLDL cholesterol from 0.028 ± 0.01 to 0.069 ± 0.01 mmol/ml. As based on analysis of variance, for the four experimental diets there was no significant effect of carbohydrate source and no fat‐carbohydrate interaction. Thus, the hypothesis was rejected. When the diets contained soybean oil, cellulose versus starch plus glucose produced significantly greater increase plasma triacylglycerols. This carbohydrate effect was not seen when horses were fed the MCT diets. The experimental concentrates did not differently influence the concentrations of plasma glucose, total serum cholesterol, phospholipids, insulin, free fatty acids and the activity of post‐heparin lipoprotein lipase. We suggest that the MCT‐induced increase in plasma triacylglycerols is related to an increase in hepatic VLDL secretion, with the extra substrate for increased synthesis of triacylglycerols being the acetyl‐CoA derived from the hepatic oxidation of medium chain fatty acids.