Review of genetic aspects of radiological alterations in the navicular bone of the horse.

This research paper explores the genetic aspects of radiological alterations in the navicular bone of horses and their influence on the development of navicular disease, also known as podotrochlosis. The researchers found a considerable variation in the prevalence of this disease in different warmblood populations and discovered that these radiological changes mostly develop genetically independent from other orthopedic health traits.

Navicular Disease and its Prevalence

• As the study explains, navicular disease or podotrochlosis causes lameness in horses’ forelimbs, bearing similarities to osteoarthritis in humans.
• Radiological examinations, such as X-rays, can detect changes in the navicular bone early in horses’ lives.
• Navicular disease prevalence varies in warmblood populations, with studies reporting rates between 14.9% and 87.6%.

Genetic Factors and Heritability

• The occurrence of radiological changes in the navicular bone is strongly influenced by genetic factors.
• Heritability estimates for this aspect, obtained through the use of animal threshold models, range from 0.09 to 0.40, indicating a significant hereditary component.
• However, the study notes that these changes mainly occur independently of other orthopedic health traits on a genetic level.

Correlation with Performance and Selection

• There is a negative genetic correlation between radiological alterations in the navicular bone and the number of tournament entries and placings, showing that horses with fewer radiological alterations tend to perform better.
• By selecting breeding horses based on their breeding values for these traits, a reduction in radiological changes and an improvement in performance can be achieved simultaneously.

Identification of QTL

• To better understand the genetic aspects of navicular disease, the researchers developed an optimised markerset to detect quantitative trait loci (QTL) associated with pathological changes in the navicular bone, particularly in Hanoverian warmblood horses.
• The whole genome of the horse was scanned using highly polymorphic microsatellites.
• The results identified chromosome-wide significant QTL on equine chromosomes (ECA) 2, 3, 4, 10, and 26, with genome-wide significant QTL found on ECA2 and ECA10.
• The identification of these QTLs linked to navicular disease will help improve the selection process for a healthy limb constitution in horses.