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Gender Selection Helps Sustain Rare Breeds

Rare breeds of horse may have another tool in their arsenal against extinction: gender selection. The gender of a foal depends on what chromosome the sperm contains when it fertilizes the ovum. The nucleus of a sperm carrying the X chromosome is 4 percent larger than sperm containing a Y chromosome. This difference allows the sperm to be separated.

Inseminating the mare with semen that contains mainly X chromosomes increases the chances of getting a filly. This is important for breeds like the Suffolk Punch, which have fewer than 300 mares in the entire world. The Suffolk Punch is an English draft bred that is known for their power, stamina and temperament.

Tullis Matson, who owns AI Services, a UK-based equine reproductive center, began using new technology to sex sort equine semen in 2019. The company works in partnership with both Cogent and Sexing Technologies, and uses specialized equipment to sex sort the semen prior to insemination of the mare.

Ruby, a Suffolk Punch owned by Nottingham Trent University, was inseminated with semen from Holbeach Iggy, a Suffolk Punch stallion owned by Mike Clarke of Holbeache Farm, Suffolk, as part of a project between The Rare Breed Survival Trust and Nottingham Trent University. Using pedigree information, the project determined which animals can be bred to one another to minimize genetic decline and the risk of inbreeding.

Ruby had a healthy filly from the procedure. This form of gender selection allows breeding populations to increase more rapidly than by using traditional breeding methods.

Read more at Equine Science Update.

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Quality Of Frozen Semen Affected By Stallion Age And Breed

A study out of Australia has found that semen from Arabian stallions withstands the freezing and thawing cycle used in artificial insemination (AI) better than semen from Icelandic, Quarter Horse or Warmblood breeds.

Drs. Jörg Aurich, Juliane Kuhl, Alexander Tichy and Christine Aurich, from the University of Veterinary Medicine in Vienna, examined the semen quality of 1,012 frozen and thawed samples from 134 stallions of five different breeds. They calculated the acceptable percentage of ejaculates for AI as well as the doses available.

The researchers found that the most important variable was sperm motility before freezing: The higher this number, the more likely quality post-thaw semen would be found. Thawed semen is considered acceptable for insemination when the sperm's ability to swim in a straight line or in large circles is 35 percent or higher.

The age of the stallion was also an important parameter; there was a marked decrease in acceptable ejaculates in stallions over 9. The researchers suggest that stallions with high breeding values used in competitions should be collected while they are younger and not after they have retired from the competition ring.

While Arabian stallions had above-average acceptable ejaculates, Icelandic and Quarter Horse stallions had below-average ejaculates. Warmblood and Lipizzaner stallions had average numbers. The researchers note that this suggests a genetic basis for semen cryotolerance.

Total sperm count was the most important variable determining the number of doses of semen obtained. Stallions with good semen quality are more likely to yield acceptable semen after thawing, but good sperm motility in raw semen doesn't always correlate to post-thaw semen quality.

The scientists concluded that there are individual stallions that have semen that does not freeze well, though their raw semen is high quality.

Read more at HorseTalk.

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