Evaluation by the heterospermic insemination technique of the differential effect of freezing at -196 C on fertility of individual bull semen

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Abstract
Replicate evaluations of the heterospermic insemination technique were made. Each semen mixture contained equal numbers of spermatozoa collected from 4 bulls. A portion of this mixture was inseminated unfrozen (control) and another part after standard freezing at -196.degree. C in liquid N and use within 2-3 days (Series A). The paternity of calves was established by blood-typing; their relative numbers defined the relative heterospermic fertility (RHF) of the bulls. The RHF of the bulls was close to 1:1:1:1 after fresh semen but not with Series A. Another portion of each mixture (Series B) was frozen at -196.degree. C for 3 1/2 yr and tested for repeatability. Lack of repeatability would suggest an effect of storage time. The numbers sired by Series A (50:13:12:36) did not differ significantly from those of Series B (52:19:23:31). The pooled data from Series A and B (102:32:35:67) differed significantly from those obtained with fresh semen (28:26:30:40). Series A and B, separately or pooled differed significantly from the 1:1:1:1 fresh semen ratio. The heterospermic fertility of individual bulls was affected unequally by the deep freezing process but not by the period of storage. The changes were traceable to an alteration in the heterospermic performance of 1 bull compared to the other 3. Possible causes of spermatozoa damage are discussed. Further study is indicated.

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