Type of Polyunsaturated Fatty Acid Supplementation Affects Red Blood Cell Fatty Acid Composition in Exercised Thoroughbreds

Omega-3 and omega-6 PUFAs are essential nutrients for horses. SC-PUFAs (<20 carbon) include α-linolenic acid (ALA, n3), linoleic acid (LA, n6), and gamma-linolenic acid (GLA, n6), while LC-PUFAs (≥20 carbon) include eicosapentaenoic acid (EPA, n3), docosahexaenoic acid (DHA, n3), dihomo-gamma-linolenic acid (DGLA, n6), and arachidonic acid (AA, n6). Eicosanoids produced from AA tend to be pro-inflammatory while DGLA, EPA, and DHA give rise to lipid mediators that are anti-inflammatory. This study was conducted to determine the effect of feeding different chain length omega-3 and omega-6 PUFAs on red blood cell (RBC) fatty acid (FA) composition in exercised horses. Thirteen fit Thoroughbred horses (age 4.1 ± 1.9 y, BW 496.0 kg ± 36.5 kg; mean ± SD) were split into 2 groups balanced for age, gender, and body weight. The horses received either 35 mL/d of a corn oil-flax oil supplement (LA-ALA) (n = 6) or 60 mL/d of a high-GLA safflower oil-fish oil supplement (GLA-EPA-DHA) (n = 7). The LA-ALA supplement provided 8.0 g LA and 10.2 g ALA per day. The GLA-EPA-DHA supplement provided 2.5 g LA, 5.4 g GLA, 0.3 g AA, 4.4 g EPA, 0.8 g DPA, and 3.8 g DHA per day. Each supplement provided a similar amount of total omega-6 and omega-3 per day. The horses were fed 4.9 ± 1.4 kg/d (mean ± SD) of a textured horse feed along with 1.0–1.5% BW/d of timothy hay and 60 g loose salt. The basal diet provided about 140 g/d LA and 62 g/d ALA. For 90 d before the start and during the study, the horses were exercised 3 times per week on a racetrack and walked 3 d per week on a mechanical walker. For 90 d before the study the horses were fed the same basal ration. Twenty-four individual FA were measured at monthly intervals in RBCs over the 3-mo supplementation period. Differences related to time and treatment were analyzed using a 2-way ANOVA. RBC FA did not change in the LA-ALA group during the supplementation period. RBC GLA, DGLA, EPA, and DHA increased over time in the GLA-EPA-DHA group (P < 0.01) and were higher than with LA-ALA supplementation after 1, 2 and 3 mo of supplementation (P < 0.01). RBC AA increased over time in the GLA-EPA-DHA group (P < 0.05). These increases in GLA and LC-PUFAs were primarily offset by decreases in RBC oleic acid (18:1n9), LA, and ALA. The ratio of RBC AA to (DGLA+EPA+DHA) was 3.9 times higher in the LA-ALA supplemented group compared with the GLA-EPA-DHA group (P < 0.01). This study found that horses fed a high LA intake and supplemented with ALA did not efficiently elongate ALA to EPA and DHA, but that horses did elongate GLA to DGLA.