In a recent Australian study, microscopic fractures were found in the front leg bones of nearly all euthanized racehorses—including those not put down for catastrophic breakdowns. The study found that older horses with longer careers had more bone damage, indicating that the injury accumulated because of chronic overload of the joints.
Dr. Ebrahim Bani Hassan of the University of Melbourne reported in the Australian Veterinary Journal that his finding suggests that racehorses may need to be better managed and offered longer breaks to ward off bone fatigue, reported HorseTalk. The study team related the prevalence of microscopic bone fractures in the lower legs of 83 Thoroughbred racehorses back to the training history of each individual horse.
The samples were from horses that were between the ages of 2 and 10, and all were from Melbourne racetracks or the University of Melbourne Equine Centre. The researchers used the forelimbs of 38 Thoroughbreds for the study and the hind limbs for the remainder. All the bones were scanned using a scanning electron microscope to detect microfractures. The bones were also assessed for bone density.
Race careers ran the gamut from no starts to 66 starts and their earnings varied by horse from $0 to nearly $2.7 million.
Of the 38 forelimbs that were examined, 21 had been in training at the time of death. The majority of these horses were euthanized because of a leg fracture. Of the 17 horses not in training, four had leg fractures that resulted in their deaths. The others died or were put down because of joint infections, intestinal issues, cardiac arrest, ligament problems, kidney issues or ataxia. Their time away from race training was between 1 and 59 weeks.
Of the 45 hind limbs that were reviewed, 24 of those horses were in training when they were euthanized. Nine of them had fractures, including one pelvis and one shoulder. The other 15 died of tendon injuries, cancer, exercise-induced pulmonary hemorrhage, gut issues and cardiopulmonary problems. Eight of the 21 horses not in training suffered from fractures, four of which involved the leg bones.
The researchers discovered that palmar/plantar osteochondral disease (a degenerative condition affecting the lower leg bones in horses) was found in 65.8 percent of the forelimb horses and 57.8 percent of the hindlimb horses that were studied. This condition is typically determined to be the result of “bone fatigue,” where damage accumulates from stress fractures or repeated loading. These types of injuries begin at the microscopic level and accumulate until they are visible to the naked eye.
Using the microscope, microfractures were seen in the 97.4 percent of the forelimbs examined. The density of these tiny fractures increased with the age of the horse and with the number of starts. Additionally, older horses with longer racing careers had more presence of microscopic subchondral bone injury, which is consistent with bone failure related to accumulated training distance.
The researchers conclude that rest from intense race training may allow for some repair of the microscopic damage, though it is not known how much damage needs to accrue before an injury is apparent. Many of the horses used in the study were reported to have been training well, with no signs of lameness prior to their euthanasia.
Read more at HorseTalk.
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