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Megaesophagus Identified as Hereditary Disease in Friesians

In November 2014, the researchers at Utrecht University Equine Clinic and Wolvega Equine Clinic confirmed what had been reported before by previous studies, that being “the predilection of Friesian horses for megaesophagus compared with non-Friesians,” with the prevalence reported to be 2.2% of those Friesian horses presented to these facilities as compared to a rate of 0.5% in horses of other breeds.

The objective of this study was to better understand the changes that occur at the cellular level of the esophagus of affected horses and to compare that to normal control horses, with an emphasis on the specific characteristics of the esophagus that are important for normal function. Friesian horses (ages two months to 26 years) that had presented to either of these clinics and had been diagnosed with megaesophagus were compared with three non-affected Friesian horses whose pedigrees were not closely related to the affected Friesians and three warmblood horses that were also included as controls. Of the 18 affected horses, only 12 had dilation of the esophagus. The researchers concluded the following with regard to megaesophagus in the Friesian horse:

  • Megaesophagus occurs more frequently in Friesian horses than in the general horse population.

  • It occurs most frequently in the first five years of life.

  • Esophageal dilation occurs most frequently in the portion of the esophagus that lies within the thoracic (chest) cavity.

  • There can be severe functional problems of the esophagus without grossly visible esophageal dilation.

  • There is increased abnormal collagen found mainly in the nondilated portion of the esophagus of affected horses.

  • This abnormal collagen can be found in very young foals, suggesting that

  • Megaesophagus has a hereditary component in Friesians.

Scientific Article: Ploeg, M. et. al. “Esophageal Dysfunction in Friesian Horses:

Morphological Features” Veterinary Pathology OnlineFirst, November 3, 2014 as dol:



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