The aim of the experiment was to determine the effect of potential antioxidants (adenosine, L-cysteine hydrochloride, ascorbic acid, magnesium fumarate and prolactin) supplementing the Biosolwens extender on semen survival time and sperm chromatin structure. The semen motility was examined every day and the susceptibility of sperm chromatin to denaturation was evaluated on collection day and day 15 of storage. The addition of magnesium fumarate to Biosolwens extender increased sperm survival but resulted in the highest increment in the proportion of sperm with damaged chromatin. Biosolwens supplemented with 200 mg of L-cysteine hydrochloride brought the best results. It is possible that lower concentrations of this component would act in a more protective manner. The examination of the chromatin structure appears to be an useful tool for investigation of semen preservation.