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Objectives:To study the effect of age and body fat on leptin levels and semen parameters of Arab horse.Methods:Fifteen fertileArab stallions of different ages belonging toPoliceAcademy were divided into three equal groups according to their age.Old horses are those of >18 yeas (18-27),Mid-age horses≥13 to18 years(13-18),Young horses are those of <12 years(7-11). Semen was evaluated three times for each stallion.Blood and seminal plasma were assayed for measuring leptin, testosterone and estradiol.Subcutaneous rump fat thickness was measured using ultrasound for estimating body fat percent and fat mass percent.Results:All body fat parameters were significantly high inYoung stallions and decreased with increasing age.As age increased, testosterone levels increases but leptin levels decreased.Age was inversely correlated with fat%, fat mass and leptin.All fat parameters had direct correlation with leptin in semen and serum but an inverse one with serum testosterone.Serum leptin directly correlated with sperm cell concentration inMid- age stallions and inversely correlated with percent of live sperm in Old stallions.Semen leptin correlated directly with both percent of live sperm and percent of abnormal sperm inOld stallions.Conclusion:This study proved that aging in stallions is related to a drop in fertility, a decrease in body fat and in t leptin.Arab stallions of age7 to18 years could be used in the breeding efficiently.