3rd August 2008
Predicting the Future with Yearling Radiographs
By Dr Chris Whitton, Senior Registrar/Senior Lecturer in Equine Medicine & Surgery, The University of Melbourne, Werribee Equine Centre.
The horse racing industry is built on future prediction, it’s what punters are doing every time they bet and breeders when they mate their mares. In recent years, yearling radiographs have taken future prediction to a new level but at considerable expense.
Radiographic repositories have become an established part of yearling sales in Australia and overseas. Australia introduced the radiograph repository to its auction sales in 2003. Thirty four views are required for submission, with an additional eight views if a horse is expected to be purchased by a Hong Kong buyer.
Taking an extensive number of radiographs of each yearling and their submission to repositories is a major undertaking that involves considerable expense. Not surprisingly, many vendors wonder if the effort and expense is worthwhile and recent research raises important issues.
Repositories have a number of important roles. Firstly, they act as a deterrent to sellers entering horses that have severe orthopaedic problems. There has been no research that has examined the effectiveness of repositories in this role. Secondly, they provide buyers with information that will enable them to make an informed decision. Current and previous research has examined the usefulness of repositories for this second role.
Before the introduction of the repository system, high value yearlings were radiographed multiple times which was not in the best interests of the horse and resulted in unnecessary exposure of personnel to radiation. With the advent of the repository, repeat examinations were eliminated but many more yearlings undergo examination.
Many of these radiographs are not examined on behalf of potential buyers. However, submission of radiographs into the repository is entirely voluntary and perhaps with time and maturity of the market, there will be rationalisation of the number of horses being radiographed.
Radiographs are a useful aid for diagnosing the causes of lameness in horses, however they have their limitations. They only form part of a complete assessment by a veterinarian and should never be considered in isolation. They are most useful for problems that involve bone and have limited use for examining soft tissues. Problems often have to be severe before they appear on radiographs, arthritis being a good example.
It is also common to have abnormal findings on radiographs in sound horses. In young horses, radiographs are useful for diagnosing osteochondrosis, a condition that affects the join surfaces of growing horses, and for identifying bone cysts.
So should we be relying on radiographs to identify potential problems in healthy young horses before they enter race training?
The answer is complex. A number of studies have examined the performance of European Standardbreds that were radiographed as yearlings.
One study concluded that there was no association between radiographic changes and performance. Others have shown that horses with radiographic abnormalities at more than one site have poorer performance but horses with problems in singles sites performed as well as horses with no radiographic abnormalities.
The first large study in thoroughbreds was performed in the United States and published in 2003. Radiographs were examined and abnormalities were recorded and categorised. The horses’ performance was then followed in their two and three-year-old racing careers. The investigators found some abnormalities that were associated with poor performance but many were not.
Changes that were associated with future performance were limited to the fetlock joint but did not include vascular channel abnormalities in the sesamoid bones. To cloud the issue, another US study restricted to lesions of the sesamoid bones only, found some vascular channel abnormalities were associated with impaired performance in horses’ careers at two and three years old.
Current work at the University of Melbourne performed by PhD student Melissa Jackson has examines radiographs presented to all the premier sales in Australia in the first year of the repositories, 2003.
Funded by the Rural Industries Research and Development Corporation (RIRDC) and Racing Victoria Ltd, this is the largest study of its kind.
A large number and variety of radiographic abnormalities were observed and the association of lesions with performance of the horses at two and three years of age were examined. Preliminary findings indicate that there were some abnormalities that were associated with future performance, however many abnormalities were not.
The abnormalities that did affect performance differed from those in the two previous investigations from the United States.
What are some possible explanations for these findings? Firstly, we do not know what treatment horses might have received for the abnormalities that were identified. Certainly many horses that perform well despite major problems identified on radiographs do so because they have been successfully treated, usually surgically. One of the benefits of surveying young horses with radiographs is that problems can be identified early and treated before they become a major problem.
Secondly, the sales process selects for less severe abnormalities. Horses that make it to sales do not have joint swelling or obvious lameness as will be seen with more severe and performance limiting radiographic abnormalities. And as discussed previously, there is the deterrent effect of the radiographic repository.
Sellers are likely to withdraw horses with sever radiographic changes if they believe the abnormality will be viewed on radiographs and significantly reduce the sales price.
Further information that is useful to both buyers and sellers will come out of the RIRCD study in the near future. In the meantime, it is reasonable to assume that although they provide useful information that assists with decision making when purchasing a yearling, it is difficult to make reliable predictions of future performance bases on radiographic examination alone.
With thanks to Chris Whitton Werribee Equine Centre. http://www.equinecentre.unimelb.edu.au/ and Inside Breeding: Inside Racing Sires Supplement 2008 http://www1.racingvictoria.net.au/index.php?option=com_content&task=view&id=78&Itemid=113