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

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Twelve light horse mares were used to determine the effects of supplementation 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 mg of CrPic daily. Supplementation was started after an 18-day adaptation period during which all mares were fed the control diet; the subsequent feeding trial lasted 36 days. During the last eight days of the trial (days 29 through 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, nonesterified fatty acid (NEFA), ureaN or insulin concentrations in daily blood samples collected every three to four days. There was a time effect (P<.0001) for NEFA concentrations in that daily concentrations increased over time. All mares responded similarly (P>.1) to two i.v. glucose tolerance tests (conducted on days 20 and 34) with regard to glucose, NEFA and insulin concentrations. No treatment differences were detected (P>.1) for plasma glucose or NEFA concentrations during an i.v. insulin challenge on day 22; however, plasma 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 controls when monitored around feeding on day 26; as expected, all mares' NEFA levels decreased (P<.0001) after feeding. During a second period of monitoring around feeding on day 36, there was an interaction (P<.0001) between CrPic treatment and time for prolactin concentrations. During an exercise bout on day 26, growth hormone concentrations averaged over all mares increased (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 minutes after exercise (P=.045). Mares receiving CrPic had greater (P<.09) lymphocyte proliferation in response to pokeweed mitogen than did control mares for blood samples drawn on day 29. In contrast, no difference (P>.1) in immune response was detected when lymphocytes were incubated with influenza virus. Overall, we conclude that CrPic supplementation in adult, sedentary mares fed a maintenance diet of Bermuda grass hay has marginal effects on metabolic, hormonal and immune responses.

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Journal of Equine Veterinary Science

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