The results obtained in freezing several consecutive ejaculates are shown in Figure 1 as averages for the ejaculates from 6 bulls. In same instances, there was an insufficient quantity of semen available to test the freezability. (Procedure: Diluted to 30 x 10^{6} sperm per ml. with 1:1 yolk-citrate, then cooled and glycerolated with an equal volume of 14 percent glycerol (percent by volume) in 2.9 percent sodium citrate. Final sperm concentration, 15 x 10^{6}. Equilibration time, 15 hours. Freezing rate, 2 deg. C. per minute from +5 deg. to -19 deg. C. then 4 deg. C. per minute from -19 deg. to -79 deg. C. Held frozen for 5 or more hours then thawed in water at 5 deg. C. and checked for motility.) [Illustration: Percent of motile sperm before and after freezing consecutive ejaculates collected within a 4-hour period from each of 6 bulls (Fig. 1)] In general, the motility before freezing improved slightly from the first to the fourth to sixth ejaculate and then declined until about the 12th or 14th ejaculate, at which point the prefreezing motility seemed to level off through the 20th ejaculate (Fig. 1). The percentage of motile sperm found after freezing and thawing followed the same trend at an average level 10 to 15 percent lower than the prefreezing level. As is readily seen from the trend lines in Fig. 1, the difference between the prefreezing motility and the post-thawing motility increased gradually after about the fifth ejaculate. Although the absolute difference did not increase greatly, the percentage of survival after freezing dropped from 81 percent on the first 5 ejaculates to 26.5 percent on the last 5 (Table 2). Table 2.--Comparison of the Freezability of 20 Consecutive Ejaculates Collected Within a 4-Hour Period (Weighted averages for 6 bulls) =================================================================== Number Prefreezing Post-thawing Ejaculate of motility motility Survival ejaculates (percent) (percent) (percent) ------------------------------------------------------------------- 1st to 5th 29 53.3 43.2 81.0 6th to 10th 26 43.8 30.2 69.0 11th to 15th 23 28.6 14.5 50.7 16th to 20th 19 18.1 4.8 26.5 -------------------------------------------------------------------