CHROMOSOME COMPLEMENT OF RABBIT BLASTOCYSTS RESULTING FROM SPERMATOZOA STORED INVITRO AT-196-DEGREES-C

Rabbit semen was collected, pooled and extended in a tris-yolk-DMSO medium. Following storage in pellet form at -196°C for periods varying up to 24 weeks, the semen was thawed and used to inseminate artificially females, which had been injected with 50 IU hCG 5h previously. Rabbits inseminated with freshly extended semen served as controls. Females were killed 6 days postinsemination, blastocysts recovered and examined for chromosome abnormalities. With increasing storage time, a decrease occurred in the number of motile spermatozoa with the greatest decline found within the first 24 h of storage. The percentage of blastocysts recovered compared with the count of corpora lutea was 69% for the control animals and 46, 52, 58, 59, 66 and 57% following semen storage times of 24 h and 4, 8, 12, 16 and 24 weeks, respectively. The frequency of chromosome abnormalities was found to increase with increasing storage time. There were 2/36 or 5.6% chromosomally abnormal blastocysts in the control group. These were a diploid/trisomy and a diploid/monosomy. Among females inseminated with stored semen, 20/130 or 15.4% of the blastocysts were abnormal with the greatest frequency of chromosome abnormalities occurring following semen storage for 24 weeks. Mosaicism was the most frequently observed abnormality and was found in 15 blastocysts. In addition, 3 triploids, 1 monosomy and 1 trisomy were present.