Frisian horses, and especially young horses, are more likely than other breeds to suffer ruptured aortas. Doctoral Candidate Margreet Ploeg has studied the causes of this serious and tragic condition.
In this condition, the aorta always ruptures at the same location, near the ligamentum arteriosum. A ruptured aorta is usually paired with the formation of a pseudoaneurysm, or thickening of the wall of the aorta. In many cases, this pseudoaneurysm is linked to the pulmonary artery.
An histological examination of the tissue indicated necrosis of the muscle tissue in the aorta wall, a defective structure in the proteins elastin and collagen, and an accumulation of mucopolysaccharides. These defects weaken the wall of the aorta and can result in a rupture. The histology results show that there is an underlying problem in the support tissues, in which elastin and collagen play an important role.
Previous research has suggested that Frisian horses may have a general problem with their connective tissue, one of the support tissues in the body, and that the problem is therefore not limited to the aorta. Frisian horses are also more prone than other warm-blooded horses to suffer from an enlarged oesophagus. Histologies of the wall of the oesophagus shows deviations in the collagen similar to that described for the aortas.
Biochemical examinations of the aorta show that a type of enzyme known as matrix metalloproeinases display increased activity at the location of the rupture in the aorta wall. The doctoral candidate also found an increase in the number of connections in the network of the protein elastin at the same location. These two findings may be part of the healing process as a result of the rupture of the aorta.
Moreover, Ploeg has concluded that Frisian horses differ from warm-blooded horses at the biochemical level in the amount of glycosaminoglycanes, a type of sugar chain that is important in tissues such as arterial walls, in the aorta and in tendon tissues, and that they differ in how they form collagen. This means that the metabolism in the support tissues of Frisian horses may differ from the metabolism in the tissues of warm-blooded horses. This is the first indication that the connective tissues in Frisian horses differ from that of warm-blooded breeds.