SPERM STORAGE AND TRANSPORT FOLLOWING NATURAL MATING AND ARTIFICIAL-INSEMINATION

Recent observations in turkey and chicken hens show that sperm storage in both species is a highly inefficient process. After artificial insemination (AI), less than 1% of spermatozoa inseminated are selected for transport to and enter the sperm storage tubules (SST). It has been shown that the sperm selection process is orchestrated within the vagina and not at the level of the SST. At least two mechanisms are involved in the selection of spermatozoa fit for sperm storage, one being mechanical (motility) and the other biochemical in nature (sperm-vaginal mucosa interactions). Furthermore, it was also observed that the sperm storage efficiency in the chicken is dependent upon the logarithm of the number of spermatozoa inseminated. From a practical standpoint, inseminations performed frequently with a moderate number of spermatozoa should be more efficient than inseminations performed with higher doses at longer intervals. Maximal filling of the SST of hens in egg production requires only 1 day for the chicken and 2 days for the turkey. By contrast, the release of sperm from the SST is about seven times faster in the chicken than the turkey hen. The efficiency of oviducal sperm storage is related to a number of factors including age of the hen, stage of the ovulatory cycle when inseminated, and, in the turkey, if the hen was inseminated before or after the onset of egg production. Two different categories should be considered among factors that affect sperm survival in vivo. 1) Factors affecting sperm storage. These factors, acting in the vaginal portion of the oviduct, regulate the migration of spermatozoa up to the SST by increasing (e.g., short intervals between oviposition and AI) or decreasing (e.g., sperm migration in prelaying hens) the barrier effect of the vagina. 2) Factors affecting sperm release. In chicken hens, the hen's age does not impair the sperm storage efficiency but rather increases the rate of release of spermatozoa, thus contributing to a shorter duration of fertility.