=Freezability of first and second ejaculates.= In the early days of artificial breeding in this country, it was commonly believed that a second ejaculate collected a few minutes after the first resulted in a larger ejaculate containing more sperm. With the development of the procedure of stimulating sexual excitement by restraint prior to collecting semen, this difference between first and second ejaculates has been greatly reduced. Still it was noted that second ejaculates frequently withstood freezing better than first ejaculates, even though restraint and stimulation of the bull occurred prior to collection of the first ejaculate. During the course of a number of experiments, it was possible to compare the freezability of 2 ejaculates that were collected a few minutes apart from the same bull. Two consecutive ejaculates were obtained one or more times from 24 bulls so that a total of 58 comparisons could be made. The mean prefreezing and post-thawing percentages of motile sperm in first and second ejaculates are presented in Table 1. An analysis of variance showed that in this comparison the differences between first and second ejaculates in sperm survival during freezing were highly significant. A later comparison of 27 first and second ejaculates from 26 bulls did not show as great a difference between first and second ejaculates in their ability to withstand freezing (Table 1). Table 1.--Comparison of the Freezability of First and Second Ejaculates Taken a Few Minutes Apart From the Same Bull ===================================================================== Number Number Prefreezing Post-thawing of of Ejaculate motility motility Survival bulls ejaculates (percent) (percent) (percent) --------------------------------------------------------------------- 24 58 1st 60 39 65 2d 62 45 74 26 27 1st 60 36 60 2d 65 40 61 --------------------------------------------------------------------- =Freezability of several consecutive ejaculates.= The fact that second ejaculates sometimes withstood freezing better than first ejaculates suggested that the maturity of the sperm might be a factor affecting freezability. An opportunity to check this idea came when 20 consecutive ejaculates were collected from each of 6 bulls within a 4-hour period. The sperm in samples collected in this manner might be expected to be less mature with each additional collection.