Methods of freezing semen:

Currently two techniques are used to freeze canine semen: the straw system and the pellet system. The earliest work done with frozen canine semen in the late 1960's froze the semen in a similar way that cattle semen was frozen. The method used was a modified technique using glass ampoules and straws. There were no successes using these early methods after about 30 attempts. The first successful inseminations with frozen canine semen did not occur until 1970, using a freezing method totally different from the straw system. This new method consisted of freezing the semen in small pellets. Unlike the straw method, pelletizing the semen allowed changes in temperature to occur extremely rapidly as the pellets were only 1/16 the volume of the .5mL straws, thus enhancing sperm viability. With time and more research modifying the freezing technique and work developing freezing media, rapid freezing and thawing procedures were developed with conception rates as high as 93%. ICSB recently produced a healthy litter of Beagles from semen frozen in 1972.

In an eight year study (1971-1979), supported by the American Kennel Club, the pellet method provided appreciably greater numbers of viable sperm cells during freezing. During this study more sperm cells were recovered with greater motility after thawing. Compared to the straw method, recovery rates of pelletized canine semen were 20% to 60% higher depending on the size of straws used.

Currently conception rates of 73% to 85% are reported by users of the straw method compared to a 93% conception rate using pellets surgically with proper ovulation timing tests on the recipient bitch. The litter size using pelletized frozen semen is averaging a normal size while the straw method will often produce smaller than normal litters.