The hypoosmotic test (HO) was used to evaluate plasmatic membrane integrity of equine chilled semen and to estimate the correlation between the results of the HO test and those from applied routine exams of semen. The semen of seven stallions was preserved at 5ºC in three different extenders. Each ejaculate was diluted in three extenders, Kenney (K), Baken with 3% of egg yolk (B3) and Baken with 10% of egg yolk (B10), and chilled at 5ºC. The total motility (MT), progressive motility (MP), spermatic vigor (V), normal spermatic morphology (NOR) and HO test were used to evaluate semen immediately after collection and at 24 hour-intervals. Spermatic longevity was defined as the time taken to the progressive motility to decline under 10%. Semen diluted in B3 had the best longevity. The results of the HO test suggest that extenders made with egg yolk preserved the membrane plasmatic. Correlation (P<0.05) between HO test and spermatic motility (MT=0.57; MP=0.59), and low correlation between HO and NOR (0.16) were observed.
equine; hypoosmotic test; chilled semen; extender