The trouble with Friesians - DVM
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The trouble with Friesians
With a recent spike in popularity—and more than 100 years of tight inbreeding—these horses are developing serious breed-specific conditions.



Hydrocephalus is a relatively uncommon disorder in horses, but in Friesians it is seen at an estimated rate of 2.5 foals per 1,000 births.1 Some researchers think the higher incidence of hydrocephalus in this breed is caused by a deformation of the jugular foramen. If this collagen-based structure fails to develop properly, a chain of events begins that may lead to fatal hydrocephalus. A nonfunctional jugular foramen could lead to internal jugular vein compression. This could disturb cerebral spinal fluid and enhance its accumulation, resulting in hydrocephalus.1 In an article documenting Friesian clinical issues, Siebren Boerma, DVM, of the Equine Clinic Garijp in the Netherlands and colleagues discuss both dwarfism and hydrocephalus and attempt to connect them genetically.1


One of the most serious clinical problems seen in the Friesian breed is megaesophagus. This problem is directly related to the suspected collagen abnormality seen in this breed.1 Megaesophagus is a chronic dilation of the esophagus, accompanied by a lack of normal muscle tone and contractile ability in the esophageal wall. It can be seen in all animals but is usually found at a very low rate in the general horse population.

In a study conducted between 2002 and 2007 by Boerma along with Marianne Sloet van Oldruitenborgh-Oosterbaan, DVM, PhD, DECEIM, of Utrecht University's Department of Equine Sciences, 45 cases of megaesophagus were recorded.3 These cases were seen at either the Equine Clinic Garijp or Utrecht University. Of these 45 cases, 41 were Friesians, and the lead researchers noted a familial predisposition among affected horses, strongly suggesting that this condition may be hereditary.

Horses with megaesophagus show a variety of progressive clinical signs, including loss of appetite, salivation, muscle wasting, mild colic and esophageal obstruction or choke. Radiography with contrast material or direct visualization via endoscopy can identify the swollen, semifunctional esophagus and confirm the diagnosis. Chronic megaesophagus often leads to aspiration pneumonia, which can be expensive to treat and may ultimately lead to fatal complications in the horse. These horses can occasionally be managed, and some do well. But the far better method of dealing with megaesophagus in Friesian horses is to identify animals affected with this condition and remove them and related family members from any future consideration as breeding animals.

Compromised immunity

Friesian horses are thought to have weakened immune systems, so many problems that affect other horse breeds only marginally tend to be worse in this breed. For example, the incidence of retained placenta is nearly 54 percent in Friesian horses compared with only 2 to 10 percent in the general equine population.1

Photos 1 and 2: The caudal aspect of the left forelimb of a Friesian mare showing an area of poor hair growth, scabs and irritated skin. This area of caudal alopecia and roughened skin is located slightly higher than in most Friesians but shows the typical dry, flaky, rough appearance seen in these horses. Allergic reaction and insect bite hypersensitivity are two of the main causes of these lesions. (PHOTOS COURTESY OF DR. KEN MARCELLA)
Insect bite hypersensitivity (excessive skin response to the bite from various seasonal insects, predominantly no-see-ems, or Culicoides species4) occurs in 18 percent of Friesian horses, as reported in one study.1 This hypersensitivity is an intense pruritic response commonly leading to hair loss (often extensive) and skin damage of the mane, tail, head and ventral abdomen (Photos 1 and 2). In many individuals, this skin damage is severe enough to render the horse unusable for prolonged periods (weeks to months) during the summer fly season. Comparatively, insect bite hypersensitivity occurred in only 8 percent of the Shetland pony population studied in the Netherlands.1 It is now thought that this Friesian condition is a familial disease with a polygenetic background. Affected animals can be treated with traditional methods, including medicated baths and topicals, insect control and repellant, corticosteroids and allergy desensitization, antihistamines and anti-inflammatory drugs. Friesians with this condition will often show a response to treatment, but recurrence is likely.


Source: DVM360 MAGAZINE,
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