The effect of added dietary soybean oil on vitamin E status of the horse.

Fourteen 2-yr-old Quarter Horses and Quarter Horse x Thoroughbreds were randomly assigned to either a control (CTRL) diet or a diet supplemented with 6.4% soybean oil (SBO). The amounts of both diets that were fed met current NRC nutrient requirements and were isoenergetic with similar nutrient:energy ratios. Venous blood samples (20 mL) were taken at d 0, 30, 60, and 90 of the experiment and analyzed for serum alpha-tocopherol, serum cholesterol, and serum triglyceride. The sum of serum cholesterol and serum triglyceride values was used as an estimate of serum total lipid. The ratio of serum alpha-tocopherol:serum total lipid was used as a measure of vitamin E status of horses. The SBO group had higher serum cholesterol concentrations (P < .001) at 30, 60, and 90 d. Serum triglyceride was not affected by diet. Serum total lipids tended to be greater (P < .06) for the SBO group. Serum alpha-tocopherol was greater (P < .001) at 90 d in the SBO group. There was a significant correlation (P < .001, r = .62) between serum total lipids and serum alpha-tocopherol concentrations in the SBO group. This correlation was not significant (P < .07, r = .35) in the CTRL group. The ratio of serum alpha-tocopherol:serum total lipid was not affected by diet. The results of this experiment suggest that vitamin E status in non-exercising, 2-yr-old horses fed currently recommended levels of vitamin E was not affected by the addition of 6.4% SBO to the diet.