growth and antioxidant status of broilers fed supplemental lysine and pyridoxine under high ambient temperature

three levels of lysine (90, 100 and 110% of ross requirement) and of pyridoxine (3, 6 and 9 mg kg-1) were used in a 3 × 3 factorial experiment to investigate the growth and blood antioxidant ability of broilers under high ambient temperature. none of the dietary supplements affected the weight gain during the starter and grower periods. although no significant differences were detected between the treatments during the entire period, high lysine level fed birds had a lower weight gain. at any levels of pyridoxine, high lysine fed birds were lighter than others. neither the lysine nor pyridoxine changed the feed intake or feed conversion ratio during the starter, grower and entire period. however there was no significant difference between the treatments for blood malondialdehyde (mda) concentration, medium lysine fed birds had lower blood mda than other ones. no significant effects on blood triglyceride, total protein and blood superoxide dismutase activity were indicated with addition of any lysine or pyridoxine level. medium lysine fed birds had decreased blood glutathione peroxidase activity compared to the birds of other treatments. it was concluded that providing the proposed dietary lysine requirement of ross strain during heat stress ensuring the best body weight gain and body antioxidant ability. higher lysine level causes the retarded weight gain due to higher excretion of arginine from the body and consequently higher lipid peroxidation.