Some FAQ’s

– About Frozen Semen

By Jamie Anderson, MA Physiol (Oxon)

What is the industry minimum standard for motility of frozen semen?

Frozen SemenThere actually is no official “minimum quality standard”, so it typically varies between 30% and 35% depending on the centre it was frozen at. It is important to remember that motility does not guarantee fertility. No lab tests are able to guarantee fertility either. The ability to produce pregnancies is your best indicator of fertility of frozen semen. Having said that, most reputable freezing companies target around 800 million sperm per dose which at a minimum progressively motile, morphologically rate of 30% yields an insemination dose containing something greater than 200 million PMMN sperm.

Why are frozen semen AI packages more costly than fresh/chilled packages?

This is due to the difference in longevity between fresh/chilled and frozen semen. Once inseminated, fresh/chilled semen will remain alive and viable in the mare for 48-72 hours; and significantly more for some stallions. Frozen semen however has a much shorter “shelf life”, and will only remain viable inside the mare for 6-12 (or perhaps even 18) hours.

This shorter longevity means that more precision is required in terms of the timing of insemination relative to ovulation; which requires a greater number of ultrasound scans, sometimes every few hours through the night. Multiple inseminations may be required depending on the availability of the semen, and the practises that individual vets and technicians adopt.

Additionally, frozen semen is more irritating to the mare’s uterus than fresh/chilled semen, and so will often cause a more intense “reaction” which may be observed as pooled fluid inside the uterus. This requires additional treatment to deal with the irritation and subsequent fluid production.

These factors all conspire to make frozen semen packages a little more expensive than fresh/chilled packages.

Is my mare a good candidate for frozen semen?

If your mare has regularly got in foal in the last few years on the first or second attempt without fluid-related complications, is between 3 and 12 years old, and has good reproductive conformation then she is probably a good candidate for frozen semen.

Older mares (13+), those with unknown fertility (maidens), those who are subfertile, or mares who have experienced delayed uterine clearance (DUC), are less likely to be good candidates for frozen semen.

How do I know if the frozen semen I am using is fertile?

The only way to be certain if it is adequately fertile, is if mares bred to the same batch of frozen have become pregnant after 3 cycles or less.

30%+ progressive motility after thawing with good velocity is a good indicator that the semen has the potential to be fertile, as do positive results from other lab tests such as mitochondrial function, membrane integrity and chromatin assays. However, it is important to realise that, at the time of writing this, laboratory tests cannot predict the fertility of frozen semen.

The frozen semen I’m using passes minimum motility standards. Does that mean it is fertile?

No. While 30%+ progressive motility after thawing with good velocity is a good indicator that the semen has the potential to be fertile, as do positive results from other lab tests such as mitochondrial function, membrane integrity and chromatin assays. However, it is important to realise that, at the time of writing this, laboratory tests cannot predict the fertility of frozen semen.

The only way to be certain if it is adequately fertile, is if mares bred to the same batch of frozen have become pregnant after 3 cycles or less.

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