Living cells, including spermatozoa, stored under aerobic conditions require oxygen to support their normal metabolism. Excessive levels of metabolites (reactive oxygen species; ROS) can cause cell damage or lipid peroxidation. The ROS and lipid peroxidation can be detected during preparation and cryopreservation of mammalian spermatozoa. The negative effects of ROS can be partially ameliorated by the action of antioxidants. The aims of this thesis were to 1) study the effects of antioxidants on cryopreserved epididymal spermatozoa from the domestic cats and to apply the results from domestic cats to cryopreserved wild felid ejaculated spermatozoa (flat-headed cats; Prionailurus planiceps) in Thailand; 2) detect lipid peroxidation and its effects on post-thaw epididymal cat spermatozoa and 3) evaluate basic seminal characteristics of captive flat-headed cats. In the first study, the semen extender was supplemented with two types of non-enzymatic antioxidants (cysteine and a water soluble vitamin E analogue Trolox). Vitamin E had positive effects on post-thaw sperm motility, progressive motility and membrane integrity. In the second study, centrifuged post-thaw epididymal cat spermatozoa were resuspended in media with or without egg yolk and with or without a transition metal (Fe2+) (which induces lipid peroxidation). Lipid peroxidation was measured by using a lipophilic dye probe (BODIPY581/591 C11). The results demonstrated that BODIPY581/591 C11 could be used to detect lipid peroxidation in cat spermatozoa. This reaction did not significantly increase during incubation unless induced by Fe2+. In the third study, enzymatic antioxidants (catalase, glutathione peroxidase; GPx and superoxide dismutase) were added to the semen extender. Lipid peroxidation was induced after thawing. Supplementation of GPx resulted in positive effects on post-thaw motility, linear motility, mitochondrial activity, membrane and DNA integrity. Although antioxidants had positive effects on sperm quality, the concentration of antioxidants used in this study did not reduce lipid peroxidation. In the last study, the basic seminal traits of captive flat-headed cats were evaluated, as were the effects of adding the vitamin E and GPx to the semen extender for flat-headed cat spermatozoa. The results demonstrated that the captive flat-headed cats were affected by teratozoospermia. The GPx had positive effects on the post-thaw quality of flat-headed cat spermatozoa in a similar manner to domestic cat sperm quality but it did not significantly affect in vtiro heterologous fertility tests. In conclusion, oxidative stress might be one of the factors causing damage during preservation of domestic and non-domestic cat spermatozoa. Post-thaw sperm quality was enhanced by the action of antioxidants
