Should we be aiming for earlier diagnosis of OCD?

Why are the first 30 days of a foal’s life just so important?

Incidents of equine osteochondrosis, flaps of cartilage or loose cartilage and bone fragment within a joint, can be career-determining – and while these lesions can develop in the first weeks of life, we don’t diagnose until the individual is a yearling – could this be done earlier?

OSTEOCHONDROSIS (OCD) can be a careerlimiting condition as well as a welfare concern for the equine athlete. With this in mind, yearlings are radiographed ahead of sale allowing first action to be taken on the farm, or for a prospective purchaser to make his or her own assessment of the commonly affected sites in specific joints, including the tarsus, stifle and metacarpophalangeal joints.

A horse with a radiographic abnormality suggestive of OCD not only can have his or her sales price affected, but an onward athletic career may be less valuable, and may be compromised.

Horses who have undergone early removal of OCD lesions have been shown to have equivalent performance to an unaffected horse (McCoy et al., 2015).

Therefore, the early diagnosis of OCD lesions may maximise racing performance and improve the welfare and value of affected horses.

Radiographs are often taken on farms in the spring / early summer of a yearling, should we be examining horses before then?

Development of OCDs

THE EARLY development of bone is the key to the possible development of OCDs and when cartilage is being converted to bone is the point in development when OCDs can form.

Reasearch in pigs, frequent sufferers of OCD, and then in horses, by Ytrehus, Bjørnar & Carlson, C & Ekman, Stina. (2007) at the Norwegian Veterinary Institute and Swedish University of Agricultural Sciences produced a study called Etiology and Pathogenesis of Osteochondrois.

It was found that the disturbance in ossification that leads to OCD is the result of failure of the vascular (blood and lymph) supply to the growth cartilage.

In the very early days of equine growth (in utero and under 30 days) the vascular system supplies the nutrients to turn the cartilage to bone i.e. ossification.

As the animal grows this ossification front progresses through the bone and joint; eventually the vascular vessels in the cartilage meet up with the same vessels in the bone, and they consolidate.

“When the foals are young, the extremity of the femur is more immature than other joint sites and has a thick layer of growth cartilage that will be transformed into bone, below the articular [joint] surface,” reported Gabrielle Martel, a DVM-PhD student working with Sheila Laverty, MVB, DACVS, DECVS, at the Comparative Orthopedic Research Laboratory at the Université de Montréal in Quebec to thehorse.com.

“This cartilage is fragile and contains many blood vessels. When these vessels are damaged, an area of growth cartilage, normally nourished by the vessels, necroses and cannot be turned into bone.

“This area is a weak zone, and it may separate from the bone when the horse exercises,” she continued.

The lesion that form can sometimes be resolved by the horse itself – the horse can heal it, the ossification front keeps progressing and the horse will be left with clean undamaged articular cartilage.

But, if that damage to the vascular is severe enough, and the horse doesn’t have the proper advancement of bone ossification, an indentation can develop.

If this is not repaired by the horse, it can either become a cyst or an OCD lesion.

The three different forms are known as:

• Osteochondrosis latens: this resolves itself (in the pig study 60 per cent were seen to resolve)

• Osteochondrosis manifesta: these repair themselves

• Osteochondrosis dissecans (OCD): which is a fracture of articular cartilage with fragment or flap and require surgery.

As seen this process is happening early in a foal’s development, however OCD is not being diagnosed until the foal is a yearling. “Early detection of subclinical lesions holds the promise to improve outcomes as exercise restriction may promote healing,” added Martel.

OCD can caused by a variety of issues including heredity, conformation, environment (exercise / confinement), nutrition (too much or too little), body weight and growth rate.

The issues can also be caused by trauma and a study in 2017 looked into foals slipping and falling as they stand and move in their early days, and what the likelihood this can have on causing a trauma site (Quantitative and qualitative aspects of standing-up behavior and the prevalence of osteochondrosis in Warmblood foals on different farms: could there be a link?).

However, nutitrition and growth rate is obvious area that can be managed by studs and breeders and has been focused on by Joe Pagan of Kentucky Equine Research (KER).

He showed in his data at Saracensponsored talks in the summer that above average and larger-born foals have a much higher incidence of OCD both on survey and that need surgical treatment – bigger is not better.

He also revealed that the month of birth can have a significant affect – foals born in April in the US, and in May in the UK, are bigger and have a higher instances of OCD.

Use of ultrasound

Radiographs of young racehorses are not generally taken until around 330 days of age, which is then it is usually too late to do anything other than operate or intervene surgically.

Some are now lookinginto methods to improve possible early diagnosis, and for nutritionists and veterinarians to discover if can we affect the resolution or the repair stage of the lesion before it becomes a “fully fledged” OCD?

Colleagues at the research laboratory in Quebec have looked into the use of ultrasonography to detect early subclinical lesions and, thus, allow early management of these lesions.

Ultrasound examinations were performed on a group of control foals and a group predisposed to developing osteochondrosis.

The images were compared to sitematched histologic samples (cartilage samples viewed on a microscope) and MRI images.

“By using this sophisticated experimental imaging methodology we were able to ensure that what was observed on the ultrasound images was reliable,” Martel said.

Ultrasonography allowed the team to differentiate between ossification variations and early OCD.

Further, it provided a multiplanar assessment (views of tissues from different angles) of surface characteristics (such as the lesion’s length, depth, and width) and was useful when used alongside radiography.

The results from an earlier study out of Laverty’s laboratory showed for the first time that ultrasonography was more sensitive than radiography at identifying clinical OCD lesions at the distal femur. But the study was conducted in foals older than six months.

Field research in Ireland

For the next arm of the research, Martel and colleagues performed ultrasound exams on 47 foals aged 27 to 166 days (less than one month to about five and a half months of age) on a large farm in Ireland.

Ultrasound and radiograph examinations were taken of the foals, which were repeated when the foals were yearlings.

The researchers found subclinical OCD lesions in six of the foals. After exercise restriction, none of the foals had lesions visible on radiography when they were yearlings.

“The concept underlying these series of studies is to detect subclinical osteochondrosis lesions as early as possible at this important site, before they become symptomatic,” explained Martel. “The lesions develop in the first weeks of life and from past studies at the University of Utrecht in Holland, it is known that some heal up to 11 months old.

“Management practices such as exercise restriction may prevent injury to the weakened cartilage affected by subclinical osteochondrosis and promote the natural healing capacity of growth cartilage,” she continued.

“The ultimate goal is to detect, manage, and monitor them as early as possible in a rapid, practical manner to, ideally, avoid surgical intervention or diminish the extent of OCD lesions and improve outcome for osteochondrosis at this site.

“However, additional research is now required to determine if this early imaging approach will achieve this desirable goal.”

Should veterinarians and managers start screening foals for femoral trochlea OCD lesions?

“Based on the results subclinical osteochondrosis lesions can be detected by ultrasonography with confidence from three months of age onward,” said Martel.

“We also detected subclinical lesions earlier, but the ultrasound screening was more challenging as the younger foals (less than three months) had a longer haircoat at the site that interfered with the quality of the image.

“We did not want to clip hair, as this would not be desirable or practical.”

In an ideal situation, she said, foals could be screened monthly up to nine months of age to determine if lesions heal or worsen during that timeframe.

However, Donnington Grove vet Charlie Schreiber MRCVS, warns we are practically some way from this goal of carrying out ultrasound on young foals, and says it will be some years yet until this could be undertaken on a farm-scale.

“There are not many exeprienced users of ultrasound yet, and at present generally foals would need to be sedated, I am not sure this is advisable,” he said, adding: “The technology is there but we are a way off yet.”

Martel confirmed this opinion: “If screening of an entire population on a farm is not an economically viable option, it would be advisable to educate breeders and farm staff how to detect sentinel early signs of an osteochondrosis problemy.”

The future?

“Additional careful prospective studies are now required in the field with large numbers of foals to provide evidence to determine, with confidence and accuracy, what management or therapeutic strategies can be employed to improve the outcome of these lesions,” sais Martel. “In the meantime, a commonsense practical approach needs to be made based on current knowledge.”

This onward research, alongside on-farm proactive approaches, and the continuing nutritional research from Pagan et al into possible predisposing factors such as growth rates and birth weights, issues which he certainly feels play their part in causing or minimising the incidence of OCDs, could revolutionise the detection and non-surgical treatment of OCDs.

However, until early diagnostic methods are improved, good farm and nutritional management using the new tools available such as KER’s Gro-Trac, alongside good basic horsemanship, remain key.