Objective—To determine the effects of advanced age on whole-body protein synthesis and activation of the mechanistic target of rapamycin (mTOR) signaling pathway in skeletal muscle of horses Animals—Six 22- to 26-year-old (aged) and six 7- to 14-year-old (mature) horses. Procedures—Whole-body protein synthesis was measured with a 2-hour primed constant infusion of 13C sodium bicarbonate, followed by a 4-hour primed constant infusion of 1-13C phenylalanine. After the infusions, a biopsy specimen was obtained from a gluteus medius muscle and activation of protein kinase B (Akt), p70 riboprotein S6 kinase (S6K1), riboprotein S6 (rpS6), and eukaryotic initiation factor 4E binding protein 1 (4EBP1) was determined with western immunoblot analysis. For all horses, inflammatory cytokine expression in muscle and blood samples was measured with quantitative real-time PCR analysis. Results—Advanced age had no effect on whole-body protein synthesis or the phosphorylation of Akt, rpS6, and 4EBP1; however, muscle specimens of aged horses had 42% lower phosphorylation of S6K1 than did those of mature horses. Aged and mature horses had similar inflammatory cytokine expression in muscle and blood samples. Conclusions and Clinical Relevance—The lower S6K1 activation for aged horses, compared with that for mature horses, could be indicative of low rates of muscle protein synthesis in aged horses. However, advanced age had no effect on any other indicators of whole-body or muscle protein synthesis or on measures of systemic or muscle inflammation, which suggested that protein metabolism and subsequently requirements may not differ between healthy mature and aged horses.

Exercise-induced changes of pro-oxidant generating substances and muscle fibre damaging enzymes are the possible causes of reduced performance in endurance horses. Therefore, this study aims to investigate on the performance of different age and gender using biochemical profile of endurance horses during 120 km endurance race. One hundred and eighty four Arabian endurance horses were physically examined and blood samples were collected post-race.&#xD;After physical examination, the MD (F, n= 44; G, n = 86) and SC (F, n = 20; G, n = 34) were identified. T-test and pairwise correlation were used for the analysis. There were significant differences in&#xD;CK, uric acid, lactate and age (P<0.0001) respectively between the gender in the MD and SC. There were significant differences in AST (P<0.0029) and GGT (P<0.0039) respectively between the gender in the&#xD;MD and SC. In conclusion age and gender significantly affect performance of endurance horses in relation to biochemical profile during 120 km endurance race. Therefore, further studies are required to determine if age, gender and biochemical profile could be used to assess performance in endurance horses.