Evaluation of Factors Contributing to Daily Within-Horse Variation of Plasma Alpha-Tocopherol Concentration

Abstract

The current study was conducted to evaluate daily within-horse variation of plasma alpha-tocopherol concentration (TOC) (Experiment 1 [EXPT1]) and to determine the effect of a single meal on plasma TOC (Experiment 2 [EXPT2]). In EXPT1, venous jugular blood samples were collected from four pregnant (6–7 months of gestation), light horse mares (8.8 ± 2.9 years of age, mean ± SD; range, 5–11 years of age) between 7:30 AM and 8:30 AM, followed by eight hourly samples, and analyzed for plasma TOC. All horses were fed 5 kg dry matter (DM) grass hay 18 hours before sample collection and received no additional feed during the sampling period. Mean within-horse coefficient of variation for TOC was 3.5% ± 0.01%. In EXPT2, seven mature light horses, four mares and three geldings (4.9 ± 4.4 years of age, mean ± SD; range, 2–14 years of age), were randomly assigned to one of two treatments (fasted [FST; n = 7] or fed [FD; n = 7]), followed by reversal of treatments 24 hours later. At 7:30 AM, FD horses were fed 2.1 kg DM grain-mix concentrate (187 IU vitamin E/kg DM) plus 3.3 kg DM mixed-grass hay, whereas FST horses received no feed. Neither group received any feed for 18 hours before 7:30 AM. Venous jugular blood samples were collected at 10:30 AM from all horses and analyzed for plasma TOC. The mean (±SD) within-horse paired-treatment difference was not significant (0.05 ± 0.12 μg/mL). The results suggest that variation in within-horse plasma TOC is relatively small over an 8-hour period in fasting horses and is unaffected 3 hours after a hay grain meal.