- In Vitro Evaluation of Frozen-Thawed Stallion Semen: A Review
Although motility evaluation has its limitations, it should be performed to obtain a minimum threshold value. In many laboratories, a minimum progressive motility of 30% is required. Subjective evaluation by a trained person using a good phase contrast microscope is adequate for routine evaluations. In scientific experiments, subjective evaluation has been replaced by the use of objective computerized image analysers. It is clear that freezing and thawing processes cause premature capacitation and acrosome reaction of spermatozoa, damage membranes and kill cells. Not all of these changes are reflected in motility, but sperm motility is a readily assayed barometer of relative cell health. Membrane and particularly acrosome integrity should be evaluated by fluorescent probes. Other tests are not in routine use, although some of them might have potential in the evaluation of frozen semen. HOS-test, particularly, could be a useful test, and it is simple to perform. At the moment, it is obvious that we need to combine several tests for fertility evaluation of frozen-thawed stallion semen. Much research is still needed in this field if we are to be able to increase the use of frozen stallion semen and get good pregnancy rates. Reliable in vitro semen evaluation methods are a prerequisite to the development of freezing and thawing techniques. Quality control of frozen semen by dependable laboratory methods is necessary before semen is distributed to the field.
The author wishes to thank professor R.M. Kenney, ass. professor Stewart Meyers, and Paul Loomis, president of Select Breeders Service, Inc., for reading the manuscript critically and for providing excellent comments.
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