Hypoosmotic swelling (HOS) as a screening assay for testing in vitro fertility of bovine spermatozoa

Semen from 5 Piedmontese bulls was subjected to the hypoosmotic swelling (H OS) test in order to determine if the results could be correlated to the fe rtilizing capacity in vitro. Semen was routinely prepared for in vitro fert ilization (IVF), with aliquots being sampled after thawing, after separatio n on a Percoll gradient and after capacitation in a medium containing hepar in. The aliquots were added to a fructose-sodium citrate hypoosmotic soluti on (100 mOsm) and incubated at 37 degrees C for 5 min. At least 200 spermat ozoa were observed at x 400 and classified according to the presence or the absence of a swollen tail. After capacitation, spermatozoa were used to fe rtilize in vitro-matured bovine oocytes (1.5 x 10(6) cells/mL); IVF was per formed in Fert-TALP medium supplemented with 6 mg/mL BSA and 10 mu L/mL hep arin in a humidified atmosphere with 5% CO2 and 5% oxygen. Presumptive zygo tes were cultured in SOF medium supplemented with 8 mg/mL,BSA and amino aci ds. There were no significant differences in the in vitro fertility of the bulls, but a significant difference was found between bulls in the response to the HOS test. The 3 assays were significantly correlated, while no sign ificant correlation was observed between the percentage of swollen spermato zoa and in vitro fertility. The HOS test does not appear to be sufficiently sensitive to discriminate between semen samples of intermediate fertility like those used in this preliminary research. (C) 2000 by Elsevier Science Inc.