Motility and eosin uptake of formaldehyde-treated ram spermatozoa

A concentration of 0.005% formaldehyde in phosphate-buffered saline (PBS) achieved complete immobilization of ram spermatozoa while also yielding good recovery of sperm motility after removal by washing. At a higher formaldehyde concentration (0.01%) recovery rate declined with increasing dilution rate. Incubation of spermatozoa in PBS containing 0.005% formaldehyde beyond 6 h at 5, 15 or 25 degrees C resulted in poor recovery rates. Of the incubation temperatures, eosin uptake was lowest at 25 degrees C. During 4 h post-wash incubation at 30 degrees C sperm motility was significantly (P less than 0.001) affected by pre-wash formaldehyde concentration which had no effect on the proportion of eosinophilic spermatozoa.