88 Factors affecting serum vitamin E status in horses

Abstract

Vitamin E (Vit E) is commonly supplemented to horses to meet NRC requirements, support performance, and treat deficiencies that may appear via blood work. Some veterinarians report horses test deficient in serum Vit E (<2.0 ug/mL), despite adequate Vit E in the diet. The objective of this study was to test the hypothesis that several factors could affect serum Vit E status in horses, including intake, access to pasture, and lab variability. Thirty horses (540.2 kg BW ± 51.5, mean ± SD) were utilized and housed at the Purina Animal Nutrition Center, Gray Summit, MO. HAY horses (n = 12) each received 2.7 kg of pelleted feed (Strategy, Vit E 334.9 IU/kg) per day plus 2.0% BW of forage (mature grass hay, Vit E 1.6 IU/kg), with no access to pasture. PASTURE horses (n = 18) each received 2.7 kg of the same pelleted feed, with free-choice access to pasture (estimated 2.0% BW/day intake, Vit E 5.1 IU/kg). All blood samples for Vit E concentration were taken at 0730 – 0800 via jugular venipuncture into serum collection tubes. Except where noted, samples were processed immediately via centrifugation with serum sent to 2 labs (Michigan State University Veterinary Diagnostic Lab, VDL, and Cornell University Animal Health Diagnostic Center, AHDC) for Vit E analysis (LC-HPLC). For 2 additional samples, blood was processed after 8 h at room temperature and after 8 h of refrigeration to see if results varied fromimmediately processed samples. Data were analyzed with GLIMMix ANOVA (SAS 9.4) for Vit E status, as well as lab and diet comparisons. All horses tested within the normal reference range (>2.0 ug/mL) for Vit E at both labs. There was a trend (P = 0.07) for a difference in Vit E status based on lab, with VDL values slightly higher than AHDC. There was a difference in HAY vs PASTURE at VDL (P = 0.004), with higher Vit E in PASTURE. There was a trend for a difference in HAY vs PASTURE at AHDC (P = 0.06), with higher Vit E in PASTURE. These differences could be explained by the higher estimated intake in Vit E intake in PASTURE, which was significant at P < 0.001. Conversely, it could be related to the form of Vit E in the diet, especially as provided by fresh grass. Statistics were not applied to the samples that underwent different handling procedures due to low numbers, but processing did not appear to greatly alter Vit E results in these 2 samples. In conclusion, horses with adequate Vit E intake all tested within normal reference range, while dietary source and/or intake, along with lab location appeared to play a small role. More work is necessary to determine why certain subsets of horses have low serum Vit E, despite adequate levels provided in the diet.