ABSTRACT : The present study was conducted to investigate the effects of butylated hydroxytoluene (BHT) supplementation on diluted, cooled and frozen-thawed ram spermatozoa. After primary evaluation of collected ejaculates, only semen samples with motility of more than 70% and sperm concentration higher than 3×10 3 sperm/ml were used for cryopreservation. The selected semen samples were then pooled and diluted 1:4 with Tris Citrate Fructose Yolk (TCFY) extender supplemented with different concentrations of BHT (0.5, 10, 2.0 and 3.0 mM). As the control, semen was diluted and frozen in the diluent without BHT. Motility, progressive motility, viability, membranes and acrosome integrity were evaluated after dilution (part 1), cooling (part 2) and freezing and thawing (part 3). The results of the first part of the experiment showed that there were no significant difference between treatments in the motility, progressive motility, viability, membranes and acrosome integrity of spermatozoa, but the results with 2.0 mM BHT were slightly better than obtained with other levels of BHT and control extender. Significantly better results (p<0.05) were observed in the second part of the experiment for cooled spermatozoa characteristics, when extender was supplemented with 2.0 and 3.0 mM BHT. Furthermore, the results obtained in the third part of the experiment indicated that, after freezing and thawing, all evaluated semen characteristics were improved significantly (p<0.05) by increasing BHT levels, with the best results obtained for extender containing 2 mM BHT. Comparison of these results with those of control diluent, the effects of supplementation were significantly (p<0.01) better. However, the higher concentration of BHT (3.0 mM) reduced the motility, acrosomal integrity, viability and hypo-osmotic swelling response of spermatozoa compared to extender containing 2.0 mM BHT. In conclusion, the results obtained in this study showed that the semen quality of rams was improved
