Effects of two different dietary sources of omega-3 highly unsaturated fatty acids on insulin sensitivity, and incorporation into the plasma, red blood cell, and muscle cell in horses

Introduction. Dietary supplementation of n-3 highly unsaturated fatty acids may lead to incorporation into cell membranes throughout the body in humans (Lund et al., 1999) and rats. The objective of this study was to evaluate the effects of two different dietary sources of n-3 polyunsaturated fatty acid on insulin sensitivity, and the incorporation into the plasma, red blood cell, and muscle cell in horses.;Methods. Twenty one mares were blocked by age, body condition score, and weight and randomly assigned to one of three dietary treatment groups. Treatments consisted of: (1) (FISH) supplemented at 142.4 mg/kg of body weight, where eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) supplied at 58.6 mg/kg of body weight of n-3 fatty acids via a commercial marine source supplement (Magnitude(TM); JBS United, Sheridan, IN) plus the basal ration. (2) (FLAX) supplemented at 149.8 mg/kg of body weight of the n-3 fatty acid alpha-linolenic acid (ALA) via a flaxseed supplement (Nutra-Flax(TM)) plus the basal ration, (3) (CONT) did not receive additional n-3 fatty acid supplementation aside from ALA that was present in the basal ration comprised of hay and barley.;Results. Overall FISH horses had lower plasma linoleic acid (LA) and alpha-linolenic acid (ALA) concentrations versus FLAX and CONT horses (P < 0.002). Arachidonic acid (ARA) concentrations in the plasma was higher in the FISH horses versus the FLAX and CONT horses (P < 0.002), with time it increased across all treatment groups from day 30 to 60 (P < 0.007) and decreased from day 60 to 90 (P < 0.008). Eicosapentaenoic acid and DHA were only detectable in the plasma of the FISH horses, where EPA increased from day 30 to 60 (P < 0.002) and DHA increased from day 30 to day 90 (P < 0.005). Red blood cell LA was lower in the FISH horses compared to the FLAX and CONT at day 90 (P < 0.020). Red blood cell ALA was not significantly different among treatments, but increased from day 30 to 60 (P < 0.001) and decreased from day 60 to day 90 (P < 0.001). Red blood cell ARA concentrations were higher in the FISH group compared to the FLAX or CONT groups (P < 0.002). Red blood cell EPA and DHA were only detected in the FISH horses from day 30 on, where EPA increased from day 30 to 60 (P < 0.001), and DHA increased from day 30 to 90 (P < 0.009). Muscle LA was lower in the FISH group at day 60 and 90 (P < 0.040) and was also lower in the FISH group when compared to the FLAX and CONT across all months (P < 0.001). Muscle ALA was lower in the FISH group compared to the FLAX and CONT groups (P < 0.004), and the FLAX and CONT groups did not differ (P = 0.94). Muscle EPA was significantly higher in the FISH group than the FLAX and CONT at day 60 and 90 (P < 0.001). Muscle DHA was significantly higher in the FISH group compared to the FLAX group at day 30, 60 and 90 (P < 0.020), and the FLAX and CONT were not different at any of these sampling points (P < 0.55). Analysis of the minimal model parameters revealed that the acute insulin response to glucose (AIRg) was not affected by treatment and increased from baseline to day 30, decreased to day 60, and increased to day 90 (P < 0.020). Insulin sensitivity (SI) was not different among treatments as well, and increased from day 30 to day 90 (P < 0.005). In addition, glucose effectiveness (Sg) was not affected by treatment, and decreased from day 30 to 60 (P < 0.050), and increased from day 60 to 90 (P < 0.020). Disposition index (DI) did result in a treatment by time interaction (P < 0.030), only at day 90 where the FLAX group was greater than the CONT (P < 0.007), and the FISH group was not significantly different from the FLAX or CONT (P < 0.34). A negative correlation was found between SI and BCS (r = -0.381, P < 0.003).;Discussion. Direct supplementation of EPA and DHA significantly increased the equivalent fatty acid concentrations found in the plasma, red blood cell, and muscle cell of equines compared to controls in this study. This study found that insulin sensitivity did not vary between treatments, but its effects could have been confounded with BCS changes, indicating that more closely controlled studies are needed. (Abstract shortened by UMI.)...