Ram semen contains sufficient quantities of superoxide dismutase (SOD) and much lower concentrations of glutathione peroxidase (GSH-PX) and catalase (CAT) to prevent oxidative damage. The anti-oxidant capacity of the sperm cell is limited, due to a small cytoplasmic component,which contains these anti-oxidants to scavenge the oxidants. However ,the concentration of these anti-oxidants may decrease considerably by the dilution of the semen. The aim of the present work was to study the effect of two anti-oxidants, namely ,glutamine and an amino acid solution (BME) in a Tris-based extender on ram sperm parameters, lipid peroxidation and anti-oxidant capacity after the cryopreservation/thawing process. Ejaculates collected from 4 Akkaraman rams were evaluated and pooled at 37◦C. Semen samples which were diluted with the tris-based extender containing glutamine (2.5 or 5mM), BME (13 or 26%), and no anti-oxidants (control) were cooled to 5◦C and frozen in 0.25-ml French straws and stored in liquid nitrogen. Frozen straws were thawed individ ually at 37◦C for 20s in a water bath for evaluation. The freezing extender supplemented with 5mM glutamine led to higher motility rate (68.0±4.4%) and hypo-osmotic swelling test (HOST) (64.1±5.5%), when compared to glutamine (2.5mM) and BME (13 and 26%) (P<0.05). No significant differences were observed regarding sperm motility and HOST, following the supplementation of the freezing extender with glutamine 2.5mM and BME (13
and 26%) after thawing. CAT activity remained significantly higher following the addition of glutamine 5mM (6.4±0.9kU/g protein), compared to the other treatments (P<0.01). The anti-oxidants at different levels were not effective in the elimination of malondialde hyde (MDA) formation and maintenance of SOD activities, when compared to the control (P<0.05). Findings showed that glutamine (5mM) supplementation in semen extenders, was of greater benefit to frozen–thawed ram sperm. Future efforts are needed to find the appropriate anti-oxidants and their effective concentrations to improve post-thaw sperm parameters (e.g. motility, membrane integrity, fertility) and anti-oxidant activities when frozen–thawed ram sperm is used.