=Freezability of epididymal sperm.= Since the freezability of bull semen seemed to be better in second than in first ejaculates and some improvement in freezability was evident through the first 4 to 6 ejaculates taken consecutively, the question of whether epididymal sperm would withstand freezing seemed to be important. Although when 20 collections were made, the later ejaculates no doubt contained fewer mature sperm, the lowered freezability could have been due to accessory gland secretions rather than changes in the sperm themselves. Removing sperm directly from the epididymis would eliminate any effect that the accessory gland secretions could be exerting. Further, if epididymal sperm could be frozen, obtaining and using semen from a bull shortly after his death should be possible. Table 3.--Freezability of Sperm in Samples Taken From the Epididymides ================================================= Prefreezing Post-thawing Bull motility motility Survival (percent) (percent) (percent) ------------------------------------------------- 1 50 40 80 2 40 13 32 3 60 15 25 4 30 15 50 5+6 40 25 62 Average 44 22 50 ------------------------------------------------- To determine whether epididymal sperm would withstand freezing, the 12 epididymides (cauda only) of 6 slaughtered bulls were flushed with saline (0.9 percent) and the sperm obtained were frozen using the same procedure as was used with the 20 consecutive ejaculates discussed earlier. Averages of the 2 epididymides from each bull are given in Table 3; the samples from bulls 5 and 6 were combined. From the data in Table 3, it is obvious that motile sperm were present after freezing and thawing epididymal samples. It is likely that further experience in handling epididymal sperm may lead to improved results. Using frozen epididymal sperm from 2 bulls, Canadian workers have produced confirmed pregnancies in 8 out of 12 cows.[8] =Freezability of washed sperm.= In the laboratory it is frequently desirable to study sperm free of the seminal plasma in which they are ejaculated. Sperm can be separated from the seminal plasma by centrifugation, removal of the supernatant plasma, and resuspension in a salt solution of known composition. Sometimes it is desirable to repeat the process. This tends to wash the sperm with the salt solution and sperm handled in this way are called washed sperm.