Preservation of Bull Semen at Sub-Zero Temperatures

Bulletin 621
UNIVERSITY OF ILLINOIS AGRICULTURAL EXPERIMENT STATION


The authors gratefully acknowledge the financial assistance given to the Department of Dairy Science in support of these investigations by the Southern Illinois Breeding Association of Breese, Illinois, and the Northern Illinois Breeding Co-op of Hampshire, Illinois, through the Illinois Dairy Breeding Federation.

The first announcement in 1951 of the successful impregnation of a cow with bull semen that had been frozen stimulated much interest and research in freezing as a method of preserving bull semen. Research during the years following 1951 resulted in considerable progress and success in using freezing as a means of holding semen for long periods of time without loss of fertility.
Between 1952 and 1957, research on many aspects of the preservation of bull semen at sub-zero temperatures was carried out in the Department of Dairy Science at the University of Illinois. Many of these investigations have aided in perfecting the freezing technique that has been adapted for practical use. Some of these findings have been published, but many items have gone unreported except for general references at scientific meetings.
It is the purpose of this bulletin to bring together the results of several experiments carried out in connection with the freezing of bull semen and to present a practical freezing procedure based on the results of these experiments and findings at other institutions. Persons interested in the development of the procedures and the reasons why certain steps are necessary in freezing semen will find the details in the first part of this bulletin. Those interested only in the freezing procedure may turn to page 35 where a practical method of freezing semen is described.
One of the first considerations in freezing semen is that of deciding which semen samples are to be frozen. Since preservation of the semen—the maintenance of the potential motility and especially the fertility of the sperm—is the primary aim, some attention should be directed to the kind of semen sample that will withstand freezing. Do the initial characteristics of the sample indicate whether the sperm will withstand freezing? Does maturity of the sperm affect their freezability?