Freezing of equine semen under two schemes of addition of dimethylformamide

The aim of this study was to evaluate the post-thawing quality of equine semen subjected to two dimethylformamide (DMF) addition schemes during freezing. Semen of five Colombian Creole horses was obtained and diluted in modified INRA82 medium with two DMF addition treatments, T1: immediate addition of 5% DMF, and T2: fractional addition of 5% DMF (during 10 min). Semen was packed into 05. ml straws and subjected to conventional freezing. Sperm motility, vitality and morphology before and after dilution were assessed. In addition, a post-thaw analysis of sperm motility and kinetics using a computerized system and the evaluation of plasma membrane integrity by the hypoosmotic test (HOS) were performed. Before and after freezing, a lower reduction in sperm motility was observed by the immediate addition of DMF (T1), compared to the fractional addition of the cryoprotectant (T2) (p\u3c0.05). Superior values of total and progressive post-thaw motility for T1 were found, while the straightness index (STR) was higher for T2 (p\u3c0.05). It is concluded that the immediate addition of DMF during freezing provides a better protection of the post-thawing sperm motility of stallion semen than the fractional addition of this cryoprotectant.