Veterinary Andrology and Reproductive Techniques

IN VITRO FERTILITY ASSAY OF SPERM

• The widespread use of AI in livestock breeding, initiated scientists to persistently develop laboratory tests that would accurately predict the fertility of sires.
• The commonly employed semen evaluation tests have been effective in controlling the quality of bovine frozen semen used for A.I. but cannot be relied upon to accurately predict fertility.
• Hence, there is a need for evolving some methods to assess the fertility of spermatozoa in vitro before it is used for AI.
• Zona-free hamster ova penetration bioassay is a recently developed technique that could be successfully employed for in vitro fertility assessment of spermatozoa.
• Zona-free ova of most mammalian species retain very strong or fairly strong species specificity, rejecting entry of spermatozoa of most other species.
• The Golden hamster is exceptional and permits sperm entry of wide variety of other species provided the sperm have completed capacitation.

The hamster egg penetration is a heterologous sperm penetration test. The ova of any species will not allow the other species sperms to enter inside even after the removal of the zona pellucida. But the hamster egg will allow the other species sperms after the zona removal by enzymatic digestion.

• Sperm penetration bioassay (SPB) has been evolved as a reliable test to assess the fertility of spermatozoa.
• Various reports also indicate that there is a positive correlation between bioassay measures and fertility.
• SPB could also be used in screening and selection of donors with high fertility for in vitro fertilization and embryo transfer studies.
• The logistics of SPB is some what cumbersome, because a colony of hamsters is to be maintained, require scheduled hormonal injections, the animal has to be sacrificed and the oocytes are to be recovered at the optimum time.
• Further, the spermatozoa to be tested should also be available at a fixed time.
• To eliminate these problems, the use of cryopreserved hamster oocytes has been attempted.
• In addition, cryopreservation of hamster oocytes has practical advantages such as long-term storage, ready supply and easy transportation of viable oocytes.
• Ready availability of hamster oocytes is essential for infertility clinics and semen banks where maintenance of hamsters is difficult.
• Now, by research in this Semen Bank, it is established that cryopreserved hamster oocytes can also be successfully utilised for SPB.

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