The factors affecting the successful freezing of bull spermatozoa

The breeding of farm animals by artificial insemination marked an important advance in technique and opened new possibilities for livestock improvement throughout the world. The storage of semen for three or four days satisfies the day-to-day requirements of a bull stud. The difficulty of maintaining semen with high fertility rates for a longer period of time causes a wastage of semen from valuable sires. There is a growing importance of progeny testing, and it would be highly convenient if the semen from a bull could be collected and stored successfully during the long period when his offspring are growing to maturity. It is evident that new methods of preserving semen for very long periods of time would not only benefit the existing artificial insemination services, but would enable good sires to be used after they become sterile or die.

The preservation of bull spermatozoa has been successfully accomplished by freezing and storing in an alcohol solution at the temperature of solid carbon dioxide. By freezing the semen, the full potential of artificial insemination can be offered to the farmer. It would thus be theoretically possible to breed to selected bulls, plan a breeding program of inbreeding, line breeding or outcrossing far in advance and be sure the semen will be available.

Since 1951, numerous investigations have been carried out to determine the factors which are successful in the freezing of bull spermatozoa. Some bull studs are using frozen semen instead of fresh semen and in turn are getting a lower conception rate with the frozen semen. There are some variables in freezing bull spermatozoa which have not been found to complete the successful freezing and obtain a high survival rate equal to that of fresh semen. These experiments were conducted in an effort to determine the effect of various treatments on the freezing of bull spermatozoa.