Dietary Capsaicin Does Not Alter Synovial Concentrations of Prostaglandin E2 or the Acute Phase Response in Aged Horses after Antigenic Challenge

Dietary capsaicin enhances disease resistance and immunity in various species. Because relatively little is known about the potential benefits of capsaicin when used on horses, this study was conducted to determine the effect of dietary capsaicin on measures of health in horses. Twelve horses were fed over 28 days a basal diet with three levels of dietary capsaicin: 0 mg (C), 50 mg (CAP50), or 100 mg (CAP100) per horse per day. Before feeding on day 0, horses were weighed, a blood sample taken, and a sample of synovial fluid from the left distal carpal joint was taken. Subsequent body weights and blood samples were obtained on days 7, 14, 21, and 28. On day 21, tetanus toxoid (TT) and an immunomodulator (EqStim) were given to each horse. On days 21 to 28, daily rectal temperature (RT) and blood samples were taken. On day 28, synovial fluid was obtained immediately after blood sampling and RT measurement. Synovial concentrations of prostaglandin E2 did not differ among dietary treatments or between days 0 and 28. No effect of dietary capsaicin on serum immunoglobulin G subclass T or α1-acid glycoprotein concentrations was observed. Serum haptoglobin was elevated (P < .0003) and RT increased (P < .05) after challenge with EqStim and TT; however, haptoglobin concentrations and RT did not differ due to diet. We conclude that the doses of dietary capsaicin fed to horses in this study had no beneficial effect on measures of joint health or the immune response in horses.