Science - July 13, 2011

Breeding horses without joint problems

Many horses used in show jumping and dressage suffer from joint problems. Wageningen research shows that selection using offspring and DNA information from stallions can lead to a substantial reduction in the complaint.

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Osteochondrosis (also known as OC) arises when the cartilage in the joints of a horse does not ossify properly. The complaint can lead to swollen joints, damage to the bones and pain for the animals. OC occurs in foals and after about a year, recovery is no longer possible. Pricey show jumping and dressage horses suffering from OC have no chance of a sporting career, fetch less on the market or have to undergo an expensive operation. That is why the equine sector wants to use a breeding program to rid the sector of OC.

The Royal Warmblood Studbook of the Netherlands, the breeding organization for show-jumping and dressage horses, provided Wageningen Ph.D. student Ilse van Grevenhof with a dataset of 811 horses. She used x-ray photos to determine whether the horses had OC in their limbs.
The breeding organization uses the stallions for selection. They are subjected to a detailed assessment of their visible characteristics such as sporting performance and OC. 'This assessment is not very reliable for determining the hereditary disposition to OC', says Van Grevenhof. 'A stallion may have a genetic disposition to OC but have been raised in favourable circumstances. For whether a horse gets OC depends not just on its hereditary disposition but also on environmental factors such as the feed and the stable floor. A stallion may not have any visible symptoms of OC but still pass the complaint on through its genes.'
That is why she also looked at the x-ray photos of 25 offspring for each stallion. There, she saw big differences in the presence of OC between foals from different stallions. She was able to use that information to calculate the hereditary disposition for the complaint. That was 23 percent. 'That is quite a lot', says Van Grevenhof. 'The hereditary disposition among horses for dressage is 15 percent and that is a characteristic that is already used a lot in selection for breeding.'
Van Grevenhof does not know which of the horse's genes are related to OC but that is also not necessary. Identifying 60,000 DNA markers for a number of stallions and comparing them with the presence of OC in their offspring will allow determination of a stallion's genetic disposition for OC through its blood. However, she will need data for several thousand horses to get this genomic selection to work. That amount of data is not available at present but will be in a few years time.

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