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Effects of a docosahexaenoic acid -rich algae supplement on plasma amino acid levels in healthy, mature horses after prolonged treatment with dexamethasone
Dexamethasone (DEX) is used to treat inflammation and off-label as a calming agent in performance horses. Long-term treatment with DEX reduces insulin sensitivity (SI) and can impair other insulin-activated pathways such as protein synthesis. We previously reported that supplementation with docosahexaenoic acid (DHA)-rich algae increased SI during prolonged DEX treatment in healthy horses. The objective of this study was to determine the effect of a DHA-rich algae supplement on plasma amino acid levels in healthy, mature horses after prolonged treatment with DEX. Eight healthy, mature horses were used in a balanced, crossover design of two 56-d periods. In each period, horses were fed a basal diet (CON), or diet + 152 g/d of a DHA-rich algae (15% CP; Algae SP-1, Alltech Inc., (ALG)) providing 21.1g/d DHA for 28 d, after which blood was sampled (pre-DEX) and 0.04 mg DEX/kg BW/d administered orally; treatment continued for 21 d, then blood was sampled (post-DEX). Plasma AA concentrations were determined every 30 min during a 2 h insulin infusion. Plasma amino acid concentrations were analyzed using PROC MIXED using repeated measures analysis, with pre-DEX baseline as a covariate. Diet had no effect on plasma amino acid concentrations with the exceptions of Lys, Met, Ala and Gln (P<0.05). A treatment by DEX interaction (P<0.01) occurred for Glu, Ser, Asn, Gly, Gln, His, Thr, Ala, Pro, Tyr, Val, Met, Leu, Phe and Lys. Within each of the CON and ALG treatments, all horses received the same diet during both the pre- and post-DEX periods and therefore the increase in plasma amino acid concentrations in response to DEX in the CON horses suggests either an increase in rates of protein degradation or a decrease in rates of protein synthesis in response to prolonged DEX administration. Daily ALG feeding appeared to mitigate these changes in plasma amino acid concentrations. Additional research is necessary to identify the mechanism of this algae effect, although we hypothesize this is due to the previously reported increased SI with ALG
Keywords: horse, amino acid, dexamethasone, docosahexaenoic acid