The use of frozen boar semen technologies to preserve genetics, reduce risk when introducing new genetics into the breeding herd, allow international distribution of genetics and provide a reserve of semen to cover emergency needs has been a goal of the pork industry for many years.

A study conducted at the University of Illinois, in collaboration with the USDA and Purdue University, was designed to help establish the parameters for successful use of frozen boar semen. The fertility effects of 1, 2 or 4 billion thawed, motile boar sperm were studied using single or double inseminations in gilts.

Semen from six selected sires was collected and shipped by PIC to the USDA National Animal Germplasm Program laboratory at Fort Collins, CO, for freezing in ½ cc. straws. Frozen semen was shipped in liquid nitrogen tanks to the University of Illinois Swine Research Center for use in the fertility trials. The experiment was conducted in five replicates using terminal line PIC gilts.

At 180 days of age, prepubertal gilts were treated with PG600, followed by Matrix (Intervet, Inc.), to synchronize estrus. All gilts that expressed estrus following Matrix withdrawal were assigned to a treatment. Gilts were allotted to treatment with each boar represented across treatments.

Multiple straws of frozen boar semen were thawed into Minitube thawing extenders to create 80 cc. doses containing 1, 2 or 4 billion motile sperm/dose. Semen was used within one hour of thawing.

Estrous detection and real-time ultrasound were each performed at 12-hour intervals to determine onset of estrus and to verify fertility and time of ovulation. Gilts were inseminated once at 32 hours or twice at 24 and 32 hours after the onset of estrus using conventional artificial insemination (AI) catheters.

Data were collected for interval from AI to ovulation, pregnancy and number of fetuses at Day 24-35. The data were analyzed for the effect of dose, number of inseminations, replicate, boar, and interval from insemination to ovulation, where appropriate.

There was no effect of either dose or number of inseminations on pregnancy rate, number of healthy fetuses or embryo survival (Table 1). There was an effect of interval from insemination to ovulation on number of fetuses and embryo survival, but not on pregnancy rate.

Optimal insemination occurred within eight hours before ovulation. Boars significantly influenced number of fetuses and embryo survival, but not pregnancy rate.

Results suggest that limited numbers of thawed, frozen sperm can be used to establish acceptable pregnancy rates and litter sizes in gilts. There was little evidence that using double insemination at 24 and 32 hours after onset of estrus or using higher numbers of sperm was advantageous. This indicates that acceptable fertility can be achieved using a single insemination with 1-2 billion thawed, motile sperm. It was also evident that the boar impacted litter size and that selection for fertility and motility after freezing may be a necessary measure. Lastly, the interval from insemination to ovulation is an important limitation to fertility when using frozen boar sperm. Insemination within eight hours of ovulation has the greatest potential for fertility.

Researchers: K. Spencer, S. Breen, J. Taibl, B. Yantis and R. Knox, University of Illinois; P. Purdy, H. Blackburn, S. Spiller and C. Welsh, National Animal Germplasm Program, ARS, USDA, Fort Collins, CO; and T. Stewart, Purdue University. Contact Knox by phone (217) 244-5177) or e-mail: rknox@uiuc.edu.