The effect of cooling rate before freezing and the temperature of the semen upon addition of DMSO on the fertilizing capacity of chicken semen stored at - 196 degrees C.

Semen was collected from Single Comb White Leghorn roosters, diluted 1:4 with Beltsville Poultry Semen Extender at 35 degrees C and cooled at various rates to 5 degrees C. DMSO was added to the semen between 10 and 120 min after ejaculation at temperatures between 15 and 5 degrees C, respectively. Following the addition of DMSO, the semen was allowed to equilibrate for 2 h in a 5 degrees C environment. The semen was then frozen at 1 degree C per min from 5 degrees C to - 20 degrees C, transferred into liquid nitrogen vapour for 4 to 10 min and then immersed in liquid nitrogen for 4 to 60 days. The thawed semen was inseminated on two consecutive days and fertility was calculated during 5 and 7 days commencing on the second day after the last insemination. In general, fertility was unaffected by the rate of cooling and the temperature at which the DMSO was added. In one trial, however, the fertilizing capacity was significantly greater if the DMSO was added within 45 min when the temperature of the semen was 15 degrees C. Approximately 42 to 71 p. 100 of eggs laid by hens during the 5 day period after the second insemination were fertile regardless of the method of cooling or the temperature of the semen when the DMSO was added. The motility of the ejaculates after thawing and before insemination varied between 15 and 55 p. 100 and this measure of physiological quality was a poor indicator of fertilizing capacity. Embryonic mortality was unaffected by the cooling and freezing procedure and hatchability of fertile eggs was not significantly different for the hens inseminated with either fresh or frozen semen.