EFFECT OF OMEGA-3 FATTY ACID SUPPLEMENTATION AND A CONTROLLED-RELEASE INTRAMUSCULAR THYROXINE INJECTION ON SERUM INSULIN CONCENTRATIONS IN HORSES

A completely randomized design experiment was conducted to examine the effects of omega-3 fatty acid and thyroxine supplementation on serum thyroxine and insulin concentrations in horses. Thirty-thee geldings and 11 mares (aged 5 to 27 yr) were stratified by preliminary 4-h postprandial serum insulin concentration. All horses were then randomly assigned to 1 of 3 treatments: control (C), daily oral omega-3 PUFA supplementation (O), or monthly controlled release IM thyroxine microparticle injection (T). The 114-d trial consisted of a d 0 baseline sample, followed by a 30-d and 3 subsequent 28-d periods, named for the month in which the sample was collected – August, September, October, November and December. At the beginning of each period, venous blood was collected to determine serum thyroxine and insulin concentrations. Thyroxine-treated horses had greater (P < 0.001) serum thyroxine concentrations compared to both C and O horses. Thyroxine-treated horses also had decreased (P = 0.001) serum insulin concentrations compared to both C and O horses. Results from this experiment indicate that IM thyroxine microparticle injection is an effective method of increasing serum thyroxine concentrations results in decreased serum insulin concentrations compared to untreated animals.