Current status of semen preservation in the ram, boar and stallion.

From the studies cited it was concluded that short and long term preservation of stallion semen has encountered major obstacles. Fertilizing capacity of extended or extended and cooled spermatozoa has been impaired. With the hydrogen ion extenders, the fertility was depressed either with or without glycerol when the semen was inseminated immediately after extension. With the cream-gel extender, fertility was not impaired when inseminated immediately after extension, but was impaired after storage at 5 C for 24 hr or in the presence of glycerol. The fertilizing capacity of extended frozen spermatozoa particularly from some stallions has been more adversely affected than that of others. These studies show that the pregnancy rate range was from 50 to 80% for raw semen from the same stallion used in the frozen studies. Pregnancy rate with this magnitude of difference must be carefully weighed in applying the results from a few stallions to the population. Sufficient information has been generated to suggest that the preservation of stallion spermatozoa is possible but the fertilizing capacity is impaired. Causes of this impairment must be further investigated. When this is accomplished, the number of motile spermatozoa needed per insemination and the frequency of insemination required for optimal fertilization reported in this review must then be reevaluated.