In mammals for getting offspring, every times needs to have successful mating with ovulation except in the bat. In bat once successful copulation can able to produce offspring continuously up to 225 days. The ability of sperm storage in the female reproductive tract is considerably found in a variety of animals including insects, fish, amphibians, reptiles, birds, and mammals. In order to store sperm, females possess specialized structures in their genital tracts, such as sperm reservoirs in mammalian species, spermathecae in amphibians or spermathecae and seminal receptacles in insects and these structures store the sperm until the time of ovulation or a time when the oocytes are transported to the site of fertilization.
Other then bats, in birds and reptiles on a single successful copulation or artificial insemination can produce many fertile eggs for longer duration of period. The female birds achieve this marvelous feat by storing the spermatozoa for longer periods in the specialized structures called as sperm storage tubules (SST) in the oviduct. These SST are situated at the utero-vaginal junction (UVJ) and infundibulum, whereas the UVJ is the primary site for the sperm storage in female reproductive tract. The duration of sperm storage varies with species viz. in chiken-28days, quail-12days, and turkey-72 days. Some of researcher found that these SST may be functional before the maturation of the ovary and oviduct.
In avian species, upon copulation or insemination, the majority of deposited sperm is lost from the vagina. About 1% of the total deposited sperm are transported through the vagina to reach SSTs in chicken whereas it is 2% in turkey. During this transportation sperms are in motile state but once they reached SSTs, become immotile and they remain in unconscious state during their storage. Motility is restored at some stage before fertilization. This restoration of sperm motility is necessary for the release of spermatozoa from the SSTs and for the penetration of the inner perivitelline layer for successful fertilization. The mechanism by which sperm becomes immotile and their release from the SSTs is still yet to be established. The survivability of sperm in the SST for a prolonged period enables female birds to produce one or more clutches of fertile eggs even after single mating or insemination.
Female reproductive tract of chicken, PC: Authors
The advantage of prolonged sperm storage and survival in the oviduct of laying birds is fully exploited and utilized in practical poultry production systems. Knowledge of the dynamics of sperm transport, selection and storage in the avian oviduct may provide insight to the investigators attempting to develop livestock breeding strategies using artificial sperm capsules. Understanding the mechanism of sperm storage in the SSTs and their subsequent release for fertilization will further improve the efficiency of artificial insemination (AI) technique wherein the superior sires can be more effectively utilized for breed improvement programs. This will also reduce the frequency of AI sparing the birds from handling stress.
The fertile period, the number of consecutive days that hens lay fertilized eggs, is about 2 to 3 wk in chickens and 10 to 15 wk in turkeys. A factor contributing to this difference in sustained fertility is that turkeys (30,566 SST) have 6.2 times the number of SST than broilers (4,893 SST). Not only is the number of SST greater in turkeys, but the length of the turkey SST is greater than that is in broiler. Furthermore, the maximum number of sperm recovered from turkey SST was 4.1 × 106, representing 1.6% of the sperm number (250 × 106) inseminated, whereas the maximum number of sperm recovered from broiler SST was 2.2 × 106, only 0.9% of the sperm number (250 × 106) inseminated. Thus, the difference in the length of the fertile period between broilers and turkeys is predominantly due to the increased numbers of SST and the subsequent increase in sperm storage capacity of the turkey compared with the broiler.
1 PhD Scholar, 2 SRF, 3 Scientist
ICAR- Central Avian Research Institute, Izatnagar
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