KFPS Royal Friesian


DNA test added to stallion selection


With the start of 2014, DNA-testing will be added to the list of stallion selection criteria.
The DNA marking tests that serve to identify the carriers of hereditary faults such as ‘dwarfism’ and ‘hydrocephalus’ in the population of Friesian horses are now virtually completed. The test will be used to test the stallions who are taking part in performance testing at the end of this year. These stallions will be tested for anomalous genes straight after the Stallion Inspection. In the next few months these tests will be further developed to make them widely available for use so that they can also be made accessible to breeders. It will be an interesting instrument for breeders to test their broodmares. The completion of this marking test represents a significant step in the process of eliminating inbred disorders of the Friesian horse.

The KFPS intends to use the DNA tests for fast and total elimination of hydrocephalus and dwarfism in foals and to gradually phase out carriers. These tests would make it possible to remove the (mutated) genes responsible for these faults from the total equine population in just one generation, simply by excluding all carriers (male and female) from breeding. But this is not a favourable strategy, mainly because such a narrowing down of the population would lead to more inbreeding, which is in fact the cause of inborn disorders. Therefore KFPS policy will not primarily focus on the exclusion of breeding animals but instead focus on the prevention of risky matches. Over time this will reduce the number of carriers within the population.

For this reason the marking tests will principally be used to avoid risky matches. Risky matches are defined as matches between mares and stallions who are both carriers of hereditary faults. A quarter of matches where both parents are carriers of dwarfism and/or hydrocephalus will result in the birth of an anomalous foal. If only one of the parents is a carrier this will never lead to dwarfism or hydrocephalus in the foal.

A gradual phase-out means that testing of stallions will start this year with the young stallions that have been selected for the Performance Test. If a stallion proves to be the carrier of one of these genes this does not automatically mean that the stallion will not be approved. However, if an animal is found to be a carrier this will be publicised following the approval. Previously approved stallions will not be tested, mainly because the marking tests appear to have a certain margin of error. Although the margin of error is expected to be exceedingly small testing of approved stallions is not under consideration. 

Over the past few years the policy to prevent risky matches has already paid off by reducing the number of foals with dwarfism or hydrocephalus to less than ten cases per year. When it comes down to choosing the right stallion, sound communication between breeders and stallion keepers, based on studbook data, is the key to success. The DNA tests will help to achieve an effective reduction in the number of risky matches.

In the next decades DNA-testing (genomics) will come to play an important role in breeding and selection with regard to health-related issues. Genomics research is widely underway and is aimed at developing DNA tests for a number of disorders and conditions in (Friesian) horses, such as osteochondritis, sweet itch, widening of the oesophagus (gullet), aortic rupture, etc.  In the course of this year the KFPS will continue to give updates on the availability and application of these tests.