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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.

Study: Though Gnarly-Looking, Orbital Fractures In Horses Often Heal Well

A horse with a broken orbital bone can be a sight to behold – the horse's head is often massively swollen and he may be unable to open the eye on the affected side. It can be impossible to imagine a horse with this type of injury ever being able to go back to “normal,” but a study has shown that most horses with occipital fractures have a good prognosis for both retaining their sight and returning to work.

A study from North Carolina University, led by Dr. Joseph Gerding, used 18 horses referred to the North Carolina State University College of Veterinary Medicine clinic for orbital fractures. The horses were injured by rearing in a confined area, running into a stationary object, or by being kicked. Fifteen of the horses had surgery to stabilize the bone.

Horses that had received kicks to the occipital bone had higher risk of trauma to the eye, vision loss or eye removal. Horses with this type of injury also had a likelihood of having fractures in other bones as well, possibly involving the sinuses and creating a massive nosebleed. If other bones were involved, the favorable outcome from occipital bone surgery becomes more guarded.

Horses that were injured from rearing may have additional complications that require more aggressive treatment. Sinus and skull X-rays and CT scans can help diagnose orbital fractures and assess if any other bones are involved.

The study team found that surgery to stabilize a broken occipital bone was often successful in restoring function and appearance, as 13 of the 18 study horses returned to their previous level of use.

Study: Ophthalmic Atropine Use May Increase Risk Of Colic

Atropine is a commonly used drug in horses with eye issues – specifically with equine uveitis – but a new study has found that it can affect more than just the equine eye: it can also increase a horse's risk of colic.

Dr. Lena Ström and her research team investigated how the drug interacts with the horse's body and found that frequent administration of atropine may reduce intestinal action, increasing colic risk. The team suggests allowing for additional time between atropine treatments to minimize colic risk, but the frequency of medication administration must focus on the horse's comfort.

The research team used two different dosing protocols on four horses to assess the effects of manually delivered atropine on the gastrointestinal system. The research team monitored the frequency of gut noise on all horses to estimate gut action.

The scientists found a decrease in intestinal action after 1 mg of atropine was given every three hours, however there was no change to gut action after the drug was given every six hours. No signs of colic were seen.

The researchers determined that atropine eye drops given at one- or three-hour intervals will accumulate in the plasma over 24 hours and cause possible intestinal complications. Atropine administered in six-hour intervals allows for the removal of the drug from plasma and limits the possibility of colic.

Read the full study here.

Another Positive For Pasture: Equine Eyes Benefit From Turnout

A recent study has found yet another reason to turnout horses as much as possible: It keeps their eyes healthy. The diversity of fungal species found in the eye is greater in horses that spend time outside.

Drs. Mary Walsh, Courtney Meason-Smith, Carolyn Arnold, Jan Suchodolski and Erin Scott used molecular-based DNA testing to identify what type of fungi were present in the eyes of 12 horses: five mares that lived outside and seven stallions that lived in stalls.

The scientists took eye swabs from each eye of the 12 horses, then extracted and sequenced the genomic DNA from the swab.

The scientists found that the equine eye is host to many fungal, bacterial and viral organisms, and that the composition and structure of fungi varied significantly between pastured and stabled horses. Though many horse owners associate these organisms with eye issues, previous studies have shown that fungi may occur naturally on the eye: between 13 and 95 percent of eye swabs performed on healthy horses were positive for fungal growth.

The team determined that horses that were exposed to a variety of plant matter, like grasses, as well as to fluctuations in temperature and humidity, are more likely to have a wider range of fungal organisms in their eyes than horses that live in stalls, where the environment is more controlled. The differences in composition, structure, and richness of fungi inhabiting the equine ocular surface is most likely affected by the housing environment in which a horse lives, they concluded.

They also noted that horses that live on pasture may be more at risk of fungal infections if their eye is injured.

Read the full study here.