24th August 2011
Predicting Osteochondrosis in Australian Thoroughbreds
RIRDC Horse Research
Article from RIRDC March 2011 issue
By:- Kao Castle, Leo B Jeffcot, Herman W Raadsma, Imke Tammen and Frank W Nicholas.
The developmental orthopacdic disease osteochondrosis (OC, also commonly known as osteochondritis dissecans or OCD) can cost breeders hundreds of thousands of dollars a year in lost sales. It is estimated that 3.5 per cent of premium yearling sales turnover is lost annually due to the condition.it affects Thoroghbreds around the world, as well as being common in the Warmblood, Coldblood and Standardbred breeds.
Research funded by the Rural Industries Research and Development Corporation (RIRDC), and with input from the University of Sydney, has developed genomic* tools, including Estimated Breeding Values (EBVs), to predict the occurrence of OC in individual horses and their progeny*. The results of the study indicate that genetic selection based on EBVs would be able to significantly decrease the number of Thoroughbred horses diagnosed with OC in Australia and New Zealand.
Currently there is no way to predict whether and individual horse is likely to be diagnosed with OC, an diagnostic methods (clinical signs, radiography or arthroscopy) are costly and time consuming. It is widely accepted that both genetic and non-genetic factors contribute to the disease, which is associated with poor race performance including fewer race starts and lower earnings in two and three year olds.
The research aimed to deliver
- An understanding of the relative contributions of genetic and environmental factors to OC in Thoroughbreds
- Computer based predictions of whether individual horses included in the study are likely to have OC-affected foals in the future
- Laboratory tests to determine whether any individual horse is likely to develop OC as a foal or pass on a tendency to develop OC to their offspring.
This research delivers the first published estimates of the heritability of OC in Thoroughbred horses.
From the data collected from 1,231 horses in Australia and New Zealand, it was found that genetic factors account for one third to one half of the variation in in OC status in the stifles, hock and fetlock in the study population. Consequently, selection against OC can be effective in Australian Thoroughbreds.
Laboratory testing to access the genetic risk of a horse developing OC at specific anatomical sites may also become possible in the future. This is an important addition to just using EBV’s because to provides insight into a horses risk profile in the absence of information from other, related horses (which EBV’s require). So if someone wanted to bring in new bloodlines from overseas, this kind of test could be very useful.
The research also identified some non-genetic factors through reviewing the work of previous researchers, including mechanical damage to cartilage and over feeding, which were likely to be contributing to thigh rates of OC in the Australian Thoroughbred population.
Australian studs generally had harder ground than New Zealand studs which could increase the probability of mechanical damage to the joints. Variable glycaemic load* resulting form supplementary feeding of meals absence of sufficient pasture could potentially also play a role.
EBV’s calculated for OC in these horses could be the basis of a computer-based test predicting the likelihood of an individual horse having offspring affected by OC. In order to calculate EBV’s for future brood mares and stallions, an ongoing program wold be required to collect pedigree and diagnostic data describing the OC status of as many Australian Thoroughbreds horses as possible. Genetic selection against OC would utilise these EBVs.
According to previous research into the disease, alterations to husbandry techniques could play an important role in reducing rates of OC. For example, many Australian studs could reduce their rates of OC simply by addressing the nutritional regime of their young horses.