Use of spermatozoa for artificial insemination. I. Fertilizing capacity of fresh and frozen spermatozoa in sows on 36 farms.

A field trial was conducted on 36 farms in the Netherlands to compare the fertilizing capacity of fresh and frozen-thawed boar spermatozoa. Four-hundred and fifty-one sows were artificially inseminated with semen than that had been frozen and thawed according to the Beltsville Method or diluted in Kiev extender and inseminated on the day of collection. Twelve boars of the Dutch Landrace and Dutch Large White breeds were used. Farrowing rates, total number of pigs per litter and number of live pigs per litter were higher (P less than .0001) for sows inseminated with fresh semen than for sows inseminated with frozen-thawed semen (79.1%, 10.6 and 9.9 vs 47.0%, 7.4 and 7.1, respectively). Farrowing rates for sows inseminated with frozen-thawed semen were higher when semen from Dutch Large White boars was used than when semen from Dutch Landrace boars was used (58.6 vs 40.9%); the pattern reversed for insemination with fresh semen (76.5 vs 81%). Boar differences based on farrowing rate ranged from 62 to 92% for fresh semen and from 29 to 72% from frozen semen. There was no inseminator effect or farm effect on farrowing rate. On the basis of these results, frozen semen used for artificial insemination under practical circumstances can be expected to result in a farrowing rate about 30 percentage points lower and a litter size about three pigs smaller than does fresh semen.