Titration of GLA Supplementation Is Linearly Related to Incorporation of DGLA into Equine Red Blood Cells

The omega-6 fatty acid gamma-linolenic acid (GLA) has received considerable research attention in other species for its anti-inflammatory properties, largely attributed to the conversion of dietary GLA to dihomo-gamma-linolenic acid (DGLA). However, there is little to no published research on supplementing GLA to horses. The objective of this study was to determine how varied levels of supplemental GLA influence the equine blood fatty acid profile. Twenty Thoroughbred horses (9.9 ± 3.7 yr; 605 ± 58 kg BW; mean ± SD) were used in a longitudinal design for 6 mo including 3 mo of supplementation and 3 mo post-supplementation. Horses were stratified into 5 groups balanced primarily for age, BW, and initial grain intake and randomly assigned to one of 5 GLA oil treatments (n = 4): 0 (control), 1.9, 3.7, 7.3, or 9.7 g/d GLA top-dressed on similar low-starch commercial concentrates (1 to 5 kg/d). Fatty acid composition of plasma and red blood cells (RBCs) was measured every 28 d using gas chromatography at a commercial laboratory. Data were analyzed using linear regression and repeated measures ANOVA (GraphPad Prism). There was a strong positive linear relationship (R2 = 0.87; [% DGLA in RBC = 0.053(g/d of GLA intake) + 0.243]) between GLA intake and RBC DGLA incorporationafter 3 mo of supplementation, indicating horses can effectively convert GLA to DGLA in a dose-responsive manner. As GLA intake increased, more DGLA was incorporated into RBCs at a faster rate. Between baseline and 3 mo of supplementation, RBC DGLA did not change at 0 g/d GLA (0.26 to 0.23; P = 0.41) but increased 164% (0.28 to 0.74; P < 0.01) at 9.7 g/d GLA. At 1.9 g/d GLA, RBC DGLA did not differ (P > 0.05) from baseline until 3 mo of supplementation and returned after one month of washout. At 7.3 and 9.7 g/d GLA, RBC DGLA was different (P < 0.05) from baseline within one month of supplementation and remained elevated after 3 mo of washout. Results indicate that higher levels of supplementation respond faster, but take longer to peak and more time to wash out. More research is needed to determine if there is an upper limit to the dose response of GLA. Although an optimal equine blood fatty acid profile has not been delineated, these results provide novel data on the impact GLA supplementation has on the equine blood fatty acid profile.