Genetics To Blame For Friesian’s Eye Issues

A study team led by Dr. Rebecca Bellone, of the University of California Davis Veterinary Genetics Laboratory, has identified a genetic variant as the cause of a painful eye condition in Friesian horses. The condition, called distichiasis, causes hairs to grow at odd angles along the eyelid; these hairs rub the cornea, making the eye irritated and painful. Severe cases may result in corneal ulceration and possibly the loss of the eye.

Distichiasis can be treated by removing the offending hairs via thermocautery, but the condition recurs in nearly 50 percent of cases. To determine the genetic cause of this condition, the scientists traced the family trees of 14 horses afflicted with the condition. The team discovered a large chromosome deletion between two genes on the ECA13 chromosome strongly associated with distichiasis.

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The team concluded that distichiasis in Friesians is a trait with incomplete penetrance, meaning that the condition may show up in some individuals with two copies of the variant, or the horse may show no sign of the condition at all. The research team noted that testing can avoid crosses that produce animals that are homozygous for the variant. Results can also be used to ensure affected horses are evaluated often to prevent irreversible corneal damage.

To read the full study, click here.

Read more at Equine Science Update.

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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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