Cover image courtesy of Scone Equine Hospital
Nick Johnson, CEO of the New Zealand Thoroughbred Breeders Association, sat down with Dr Frances Peat BVSc PhD MS PGCertSc DACVSMR and Dr Dave Keenan BVSc MANZCVS at Karaka to discuss the results of an eight-year study into American yearling pre-sale x-rays.
The study overview
Dr Peat has a PhD in pre-sale x-ray imaging and was part of the team that looked at 2795 North American yearlings who went through sales in Kentucky. The study focuses on radiographic findings in the proximal sesamoid bones of the fetlock and the medial femoral condyle of the stifle, seeking to determine how these findings impact future racing success. One of the key factors in this study was to look at the changes in a horse between yearling time and breeze-up sale time.
“Essentially, there was an eight-year research project done in Kentucky, looking at sales x-rays and what the impact was on race performance, including if they got to the races. Pre-sale x-rays has been a subject to debate for the long time, and now these findings have been released,” said NZTBA’s CEO Nick Johnson.
CEO Nick Johnson | Image courtesy of New Zealand Thoroughbred Breeders Association
“The findings demonstrate that veterinarians have been quite cautious in the past and this has had a negative impact on sales. My motivation is to get the information to vendors and buyers so they are aware of the research, and they can speak to vets about the research.
“In the past, there have been some breeders who have stopped breeding because the impact of negative x-rays on sales. Hopefully this will see breeders return to breeding and the sales ring, and we’ll see breeding flourish.”
“Research shows cautious x-ray grading has hurt sales. By sharing these findings, we aim to boost breeder confidence, bring them back to the sales ring, and help the industry thrive.” - Nick Johnson
“There are two areas of the horse which are discussed in this study, being sesamoids and stifles, and the research compiled a grading system for x-rays based on actual racing outcomes with a grade one result having little to no impact on soundness.”
Stifle Lucency
Of the horses in the study, 85 per cent made it to the races, meaning that one in seven horses didn’t make it to the races. Approximately 10 per cent of sales horses have a ‘stifle lucency’ and most of those were grade 1 (the lowest grade).
The study asked the question – do these get worse or improve between yearling sale and breeze up sale? The answer was that only 20 per cent of horses get worse, with the rest staying the same or improving.
Then the question – do these affect the chance of getting to the races? Grade 1 and 2 luciences showed no change in the chance of racing, staying at 85 per cent. Of the Grade 3 horses, 78 per cent got to the races.
Sesamoid x-rays
The study built on previous studies around sesamoid x-rays, looking at bone shape, vascular channel depth and width, and fragments.
Around 40 per cent had an issue at Grade 1 level with only 5 per cent having Grade 3 issues. Incredibly, 97 per cent of horses rated as Grade 1 improved stayed the same or improved between yearling and breeze ups and overall most horses improved, even those with major Grade 3 issues as yearlings.
Dr. Frances Peat | Image courtesy of New Zealand Thoroughbred Breeders Association
The study found that horses rated as Grade 1 as yearlings had zero impact on racing performance. There was some reduced performance for more severe issues with Grade 3 rated sesamoids in forelimbs having an impact on getting to the races with fewer starts for those who did race, and Grade 3 in hindlimbs had no impact on the chance of racing but did cause a delay in getting to the races.
Fragments present in forelimb sesamoids also had an impact on getting to the races. As Dr Peat says, “Knowing the numbers around how much reduction of probability it is and also what the impact is (for each horse), because if it’s a case the horse might start later vs it might not race at all, these are obviously things to take into account in your discussions with your own vet for how the evidence applies to your situation.”
“Knowing the numbers around how much reduction of probability it is and also what the impact is (for each horse) - these are obviously things to take into account in your discussions with your own vet for how the evidence applies to your situation." - Dr Frances Peat
The upside of the study
The horses with Grade 3 issues proven to affect performance is around 1% of horses that were in the study, and of the 10 per cent of horses rated as Grade 1, most improved between yearling sale and breeze up sale.
“As someone who represents breeders and is passionate about breeding industry, I think it’s important that vital research like this gets out to farms and breeders, as it’ll ultimately allow people to sell more horses,” said Johnson.
“I think it’s important that vital research like this gets out to farms and breeders, as it’ll ultimately allow people to sell more horses." - Nick Johnson.
Audience questions
One of the audience questions asked was about whether this study translates to New Zealand, and the answer was that they believed it would for two reasons. One that the horses involved raced all over the world, and the other being that the gap between yearling sale and breeze up sale in America is much shorter than down here, so there is less time to develop than here, with more pressure on these horses, and yet, they still improved.
A significant difference with this grading system, compared to older methods, is that previously, any mark on an x-ray was flagged as a problem. The new system categorises issues into three levels of severity, which explains why horses used to “fail” an X-ray under the old approach but could still go on to perform well. They were likely only a Grade 1 under the new system but were previously grouped with the more severe Grade 3 cases.
“This study has enabled us to have facts across a big number of horses and we now know that 80 per cent of horses improve over time,” said Dr Keenan.
“This study has enabled us to have facts across a big number of horses and we now know that 80 per cent of horses improve over time.” - Dr Dave Keenan
“It’s worth understanding because the purpose of x-ray repositories is to give confidence to buyers,” said Dr Peat.
This study reveals that 85 per cent of horses successfully made it to the races, demonstrating that minor issues have no significant effect on achieving this milestone. However, a small percentage of horses with Grade 3 issues experienced some impact on both reaching the races and their total number of starts.
Horses who had issues as yearlings were 80 per cent likely to improve when they were re-presented for sale as breeze up 2-year-olds five months later.
