Effects of chromium tripicolinate supplementation on plasma hormone and metabolite concentrations and immune function in adult mares

Twelve light horse mares were used to determine the effects of supplementat ion with chromium tripicolinate (CrPic) on carbohydrate and fat metabolism and immune function. Mares were randomly assigned (six/treatment) to either a control diet of good quality Bermuda grass hay or the same diet plus 5 m g of CrPic daily. Supplementation was started after an 18-day adaptation pe riod during which all mares were fed the control diet; the subsequent feedi ng trial lasted 36 days. During the last eight days of the trial (days 29 t hrough 36), all mares were restricted to one-half their previous intake to test the interaction of CrPic supplementation with nutritional stress. Chromium supplementation had no effect (P>.1) on plasma glucose, nonesterif ied fatty acid (NEFA), urea N or insulin concentrations in daily blood samp les collected every three to four days. There was a time effect (P<.0001) f or NEFA concentrations in that daily concentrations increased over time. Al l mares responded similarly (P>.1) to two i.v. glucose tolerance tests (con ducted on days 20 and 34) with regard to glucose, NEFA and insulin concentr ations. No treatment differences were detected (P>.1) for plasma glucose or NEFA concentrations during an i.v. insulin challenge on day 22; however, p lasma insulin concentrations were higher (P<.002) in the CrPic supplemented mares at five and 10 minutes after insulin injection. Mares receiving CrPic had lower (P=.033) plasma NEFA concentrations than co ntrols when monitored around feeding on day 26; as expected, all mares' NEF A levels decreased (P<.0001) after feeding. During a second period of monit oring around feeding on day 36, there was an interaction (P<.0001) between CrPic treatment and time for prolactin concentrations. During an exercise b out on day 26, growth hormone concentrations averaged over all mares increa sed (P<. 0001); however no differences (P>.1) in response to exercise were detected between groups for any hormone or metabolite except that prolactin levels in control mares were higher than CrPic supplemented mares for 80 m inutes after exercise (P=.045). Mares receiving CrPic had greater (P<.09) lymphocyte proliferation in respo nse to pokeweed mitogen than did control mares for blood samples drawn on d ay 29. In contrast, no difference (P>.1) in immune response was detected wh en lymphocytes were incubated with influenza virus. Overall, we conclude th at CrPic supplementation in adult, sedentary mares fed a maintenance diet o f Bermuda grass hay has marginal effects on metabolic, hormonal and immune responses.