Dietary omega-3 fatty acid supplementation does not impair vitamin E status or promote lipid peroxidation in growing horses

Abstract

Omega-3 (n-3; ω-3) fatty acids (FA) are often included in the diet for their potential health benefits. However, because oxidative potential is increased with the degree of unsaturation in vitro, polyunsaturated FA such as eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) may be at increased risk of lipid peroxidation. We aimed to determine the effects of dietary n-3 FA supplementation on antioxidant status and lipid peroxidation in yearling horses. Quarter Horses (mean ± SEM; 14.6 ± 0.2 mo) were randomly assigned to receive no n-3 FA supplementation (CON; n = 6) or 60 mg n-3/kg body weight from milled flaxseed (FLAX; n = 6) or encapsulated fish oil (FISH; n = 6). All horses received a basal diet of mixed grain concentrate fed individually at 1.5% body weight (dry matter basis) and ad libitum bahiagrass pasture forage. Blood samples were obtained before and after 70 d of supplementation to evaluate vitamin E, selenium, lipids, antioxidant status, and oxidative stress. Data were analyzed using a mixed model ANOVA with repeated measures. Supplementation with n-3 FA did not reduce serum vitamin E or Se and, in fact, elevated (P ≤ 0.0003) vitamin E status in FISH horses. At day 70, serum triglycerides were lower in FISH and FLAX horses than CON horses (P ≤ 0.02) and F2-isoprostanes were lower in FISH than CON horses (P = 0.0002). Dietary n-3 FA had no effect on cholesterol, reduced and oxidized glutathione, glutathione peroxidase, and thiobarbituric acid-reactive substances. In growing horses fed to meet their vitamin E requirements, supplementation with 60 mg n-3/kg body weight did not negatively affect vitamin E status or promote lipid peroxidation. Elevated vitamin E status in horses fed FISH, coupled with lower serum F2-isoprostanes, further suggest that the longer-chain, highly unsaturated n-3 FA, EPA and DHA, may actually attenuate lipid peroxidation.

Keywords: equine; fish oil; flax; oxidative stress.

Figure 1.

Mean ± SEM serum vitamin E (A: μg/mL, B: μg/mg cholesterol + triglycerides) and C) serum selenium (Se) in yearling Quarter Horses before (day 0) and after 70 d of no n-3 supplementation (CON, n = 6) or 60 mg/kg body weight n-3 fatty acid supplementation per day in the form of milled flax (FLAX, n = 6) or encapsulated fish oil (FISH, n = 6). Overall effects of time (P = 0.007, P = 0.012, P < 0.001), treatment (P = 0.175, P = 0.114, P = 0.442), and time × treatment (P = 0.007, P = 0.009, P = 0.262), for panels A, B, and C, respectively, as determined using a repeated-measures ANOVA. ^abBars with unlike letters differ (P ≤ 0.05). ^cdDay 0 differs from day 70 across treatments (P < 0.0001).

Figure 2.

Mean ± SEM serum F2-isoprostanes in yearling Quarter Horses before (d 0) and after 70 d of no n-3 supplementation (CON, n = 6) or 60 mg/kg body weight n-3 fatty acid supplementation per day in the form of milled flax (FLAX, n = 6) or encapsulated fish oil (FISH, n = 6). Overall effects of time (P = 0.0008), treatment (P = 0.226), and time × treatment (P = 0.03) as determined using a repeated-measures ANOVA. ^abc Bars with unlike letters differ (P ≤ 0.05).