Image courtesy of Lesley Warwick

Ray of Light

US study finds lesions on stifles, sesamoids not as detrimental to racetrack success as many believe

The assessment of radiographs by veterinarians and the amount of risk their clients are willing to take can make or break a vendor’s yearling sale season, causing much angst and have a big impact on breeders’ end-of-year financial bottom lines. 

Many commercial breeders are currently undertaking x-rays of their 2022 foal crop to help determine their course of action ahead of the 2024 Australasian yearling sale series, mitigating their own risk as much as possible, and the revealing nature of those radiographs and their subsequent assessment by veterinarians often leading to whether those horses make select sales and when and where they are sold.

There is a US study which has recently found buyers – and veterinarians – may be placing too much emphasis on the results of the x-rays on sale yearlings and two-year-olds when making decisions about which horses to buy and for how much.

Vendors around the world, and many veterinarians, are united in the hope that buyers take those findings on board.

The study, conducted by Colorado State University and led by Dr Frances Peat, assessed the radiographs in the repository of 2,508 yearlings at the 2016 Keeneland September Sale – representing 10.9 per cent of the 2015 foal crop and 36 per cent of the yearlings sold in the US that year – and 436 two-year-olds across all major North American two-year-old sales in 2017.

Researchers also matched radiographs for horses who appeared at both yearling and two-year-old sales to help understand horses’ developmental changes detected in x-rays.

In examining x-rays of stifle lesions, the study showed:

  • The vast majority of horses as yearlings and at two were grade zero for lucencies in the stifle. Of those who had some lesions (9.6 per cent of yearlings and 11.2 per cent of two-year-olds), grade one was the most common, followed by grades two and three respectively.
  • Forty-five percent of horses who had grade one lesions as yearlings had the same condition as two-year-olds while 36 per cent improved to be considered grade zero. 
  • There was no significant difference in racing performance for horses with any lesions in the stife and 85 per cent of yearlings in the study cohort started at least once by the end of their four-year-old season. The probability of a horse with a grade three lesion starting in a race was lower (77.6 per cent) than the probability for a horse with any other grade (84.3 to 91.3 per cent), but the difference was not statistically significant in mathematical analysis.  

Well-known Australian vet Dr Chris Lawler cited a local study conducted by Dr Josie Leutton who found that only seven per cent of horses with any level of stifle lesion went on to develop overt lameness in training, regardless of the size of the lesion.

“In other words 93 per cent of them will be OK – pretty good odds in my opinion,” Dr Lawler told ANZ Bloodstock News. 

“Given this percentage, it is hardly surprising that those ‘brave souls’ who risked purchasing horses with stifle lesions in the early days of sales radiography were, on the whole, rewarded handsomely. They usually purchased these horses at a heavily discounted rate.”

However, in the current market, he said the “discounts” received for those perceived faults rarely eventuated at the yearling sales with an educated buying bench and a small pool of veterinarians with a deep understanding of the lesions and their effect or otherwise on a horse’s soundness. 

Lawler said: “Nowadays the market has caught up and most of these horses bring close to the value they would have if they were presented with no lesion at all.”

Melbourne veterinarian Dr Johnnie Walker said the impact of x-ray results on a buyer’s willingness to bid depended largely on the purpose they were selecting the horse for.

“Veterinarians will have in their mind a level of risk that they are or aren’t prepared to accept on behalf of their clients. Some veterinarians take a zero risk approach and other veterinarians are accepting of risk with their clients. Then there’s what’s really fit for purpose,” Dr Walker said.

“If you’re trying to buy a colt to trade to Hong Kong eventually, the standard in which Hong Kong is prepared to accept is really high. 

“You will hear about horses who failed Hong Kong but went on and won another three Group 1s or whatever, or horses that failed the vet and the trainer comes out and says they’ve never had a problem with the horse in its life. 

“That’s not the vet’s fault in Australia, that’s the standard set by the Jockey Club, if you like. So, what might be acceptable for someone to buy and race in Australia is different to someone who wants to buy a horse and then eventually have it accepted to trade up into Hong Kong.”

In the sesamoiditis part of the study, which also used a zero to grade three ranking system to illustrate the severity of the lesions, Dr Lawler said Australian veterinarians used a slightly different grading system for osteo lucent channels which are greater than two millimetres in width. 

One channel was considered to be mild risk, two channels was moderate risk and three channels was labelled as severe and Dr Lawler said management of those horses in the higher risk categories, particularly two-year-olds, was vitally important.

“I have two major clients that have purchased horses with mild sesamoiditis in a front sesamoid where the sesamoid has subsequently ‘given way’ –  the suspensory branch has torn off the affected sesamoid in their first preparation,” Dr Lawler said.

“These horses don’t fit their training regimes and both clients have instructed me to not let them purchase a horse with any level of sesamoiditis in front. 

“I can’t argue with their experiences and they won’t change their regimes. Other clients will be more conscious and not commence pacework with these horses unless they have obtained an up-to-date set of radiographs and scanned the suspensory branch attachment to the sesamoid.”

The US study found 85 per cent of the yearlings and two-year-olds from the 2015 crop had no sesamoid abnormalities while horses graded zero, one and two made the races from 84.3 to 91.3 per cent of the time.

Importantly, those horses in the grade three category raced 77.6 per cent of the time, no later than as a four-year-old, a decrease that was deemed not to be statistically significant by researchers.

In yearlings who were pinhooked into two-year-old sales, 72 per cent of grade one faults evident on radiographs had dissipated by the time the horses had turned two.  

The average age of horses assessed in the study that were deemed to have grade three sesamoiditis had their first start in the two-year-old season, only a few weeks later than horses with horses with lesser or no abnormalities.

“Some x-ray findings do change and some x-ray findings do not change, so it is really hard to pin down and be categorical in the advice that you give,” Dr Walker said. 

“It is very much a gut feel as to what level of risk you’re prepared to accept for what purpose that horse needs to race and then overlay price on it.”

He added: “So, an extremely well-bred filly with horrendous x-rays, you might be looking to say, ‘what is she worth to me as a broodmare?’. 

“If you think the risk of her making the races is high, but there’s a really nice, averagely bred colt that you think you can get a lot of money for this horse if he was to be traded to Hong Kong if he was good enough, but then his x-rays have to be faultless.

“If he has to be resold as a breeze-up horse, then his x-rays have to be spotless on the horse as well, so fit-for-purpose is a really important factor when considering the advice that you give to a buyer.”

American veterinarians discussed the findings at a recent forum, which led Dr Nathan Mitts of Peterson & Smith to suggest that management of milder forms of sesamoiditis was, in many cases, too conservative.

It is a conclusion drawn from the research that Dr Walker agrees with.

“If a horse is not in constant work, their bones will turn to chalk. They need to be worked, particularly a young horse who is still growing,” he said. 

“Their bones aren’t concrete. Bones are living organisms and it changes with exercise. So, if you want the front of its shins, the front of its cannon bones, the bones in its knees to be stronger, you actually have to stimulate the body to make them stronger.” 

He likened the management of horses to negating astronauts’ disease.

“These blokes who went up into space early days and floated around in weightlessness for six months and then came back to earth, their bones were chalk. They just turned into violet crumble. They weren’t exercising and loading the bone,” Dr Walker said.

“Certainly the clients I advise, we’re very conscious of astronauts’ disease. We’re very reluctant to leave horses sitting in paddocks for six months doing nothing.

“Even if it has an issue, you can modulate its exercise, but giving them no exercise is [counterproductive].”

Dr Walker hopes the US study may convince some risk-averse buyers to consider the statistics. 

“The answer to that study is that it is a positive step in the right direction for those who would otherwise be reluctant to take a risk,” Dr Walker said. 

“I think it will encourage some people to take more risks than they otherwise would – don’t worry, there are veterinarians out there who are ‘zero risk’ – and providing you overlay that with fit-for-purpose, that is an important consideration, I think it’s a positive for the vendors because that study should ameliorate the risk that some people otherwise would not take.

“It gives them an argument.”

Article written by Tim Rowe, ANZ Bloodstock News