THE RELATIONSHIP BETWEEN FERTILITY AND POST-FREEZE MOTILITY OF BULL SPERMATOZOA (BY PELLET FREEZING) WITHOUT GLYCEROL

Glycerol has been the most widely-used protective agent for the freezing of bull semen. However, Nagase, Graham & Niwa (1964) demonstrated that bovine spermatozoa could be frozen without the addition of glycerol. The purpose of this experiment was to determine whether a relationship exists between the motility of an individual bull's semen after subjecting it to the stress of freezing without the protection of added glycerol and the fertilizing capacity of that animal's semen after freezing by commercial means. Semen used in this study was obtained from adult bulls in regular use at a commercial bull stud. Motility, volume and sperm cell concentration were recorded and a 0\m=.\5ml sample was taken from the first ejaculate of each bull immediately after collection. The 0\m=.\5-mlsemen sample was diluted in 1\m=.\5ml of a solution containing 18\m=.\5g of raffinose/100 ml of water and 20% egg yolk by volume. The sample was then cooled slowly from 37° C to 5° C and was frozen 4 hr after collection, on dry ice using the pellet freezing method develo- ped by Nagase & Niwa (1964). This method consisted of placing three drops of the extended semen in a depression on the surface of a block of dry ice. The pellets were removed from the dry ice after a period of 15 min and placed in a 1-ml isotonic saline solution to thaw at 5° C. The thawed samples were then evaluated microscopically for motility immediately after being brought to 37° C on a warming plate. Several samples from each bull were evaluated, using this technique, during a 3-month period to gain a representative assessment of the semen motility. The 60- to 90-day, non-return rate for the months most closely associated with the test-freeze period was used as the measurement of the fertilizing capacity of the semen from the bulls being tested. Data from twenty-one different sires are shown in Table 1 and correlation coefficients were determined for the variables being tested, as shown in Table 2. The data in Table 2 shows that the relationship between the after-freeze motility and the 60- to 90-day, non-return rate was correlated with a coefficient of 0-67 which significantly differs from zero (P<0-01). The correlation coeffi¬ cient value between before-freeze motility and the after-freeze motility also was