Bacterial infections in foals behind some joint issues – study

Hock: Complex and large lesions in the sepsis cohort.
Complex and large lesions in the sepsis cohort of the left hind hock of a horse in the study. (a) shows multiple fragments (between arrows) superimposed on the talus. (b) shows three mineralised bodies and three radiolucent defects in the right hind fetlock of the same horse. (c) shows a large mineralised body (between arrows) in the horse’s right hind hock. There is also a small mineralised body with an associated radiolucent defect (between arrowheads) at the cranial distal intermediate ridge of the tibia.

Some of the bone lesions affecting the joints of Standardbreds are caused by bacterial infections at a young age, researchers have concluded.

The study team found that Standardbreds who survived bacterial infections before the age of six months had more osteochondral lesions than those of the same age who suffered no such infection.

The implication of the findings is that some of the lesions in this group were caused by bacteria, Eli Hendrickson, Sigrid Lykkjen, Nils Dolvik and Kristin Olstad reported in the journal BMC Veterinary Research.

Young Standardbred horses frequently develop fragments in joints.

Some fragments represent the bone condition osteochondrosis; others are considered developmental, but it is uncertain whether they result from preceding osteochondrosis.

Coldblood Trotter of mixed Swedish and Norwegian lines. Photo: Don Wright CC BY 2.0 via Wikimedia Commons
Coldblood Trotter of mixed Swedish and Norwegian lines. Photo: Don Wright CC BY 2.0 via Wikimedia Commons

Osteochondrosis occurs as a consequence of failure of the cartilage canal blood supply and ischaemic chondronecrosis.

In foals predisposed to the condition, the failure is associated with incorporation of vessels into bone.

However, bacterial vascular failure was also recently documented in foals suffering spontaneous infections, proving that bacteria can cause osteochondral lesions in foals up to 150 days old.

The study team from the Norwegian University of Life Sciences set out to determine the prevalence of fetlock and hock lesions in seven-month-old Standardbreds who had survived infections before the age of six months. They compared the results to the prevalence reported in three previous Standardbred studies.

The researchers used 28 Standardbreds, comprising 17 males and 11 females, who had been diagnosed clinically with bacterial infections within six months of birth.  The infections ranged from sepsis, omphalitis and septic arthritis to pneumonia and diarrhoea/enteritis.

The first picture (a) shows a focal, uniformly radiolucent defect (between arrows) in the left hind fetlock of a horse. There is also a mineralised body (between arrowheads), referred to as a fragment. (b) shows the left hock of a female Warmblood horse at 46 months old, diagnosed with sepsis at 6 days old; there is a pointy, bone radiopaque protrusion (between arrows), referred to as a spur. (c) At 4 months and 10 days old, the projection demonstrates focal, radiolucent defects (between arrows; osteochondrosis) in the contour at the same site as the spur in b.

The average age at diagnosis was 41.3 days. All had been treated at the Norwegian University of Life Sciences.

Eight x-ray joint images from each of the horses had been taken at the university when the horses were aged about seven months. They were examined to detect bone-related joint lesions.

Osteochondral lesions were detected in one or more joints in 19 of the 28 horses for an overall prevalence of 67.9%. Lesions were identified in the fetlock joint of half the horses, and lesions in the hock joint were found in 39.3% of the 28 horses.

The problems were found to be at least twice as common when examined against the comparison groups.

“It may,” the researchers said, “become necessary to develop methods for differentiating between acquired, septic and aseptic, heritably predisposed lesions.”

They suggested the most likely way to differentiate clinically would be a polymerase chain reaction (PCR) test on synovial fluid for a panel of common bacterial species.

“This is something we would like to explore, because it could be useful in valuable coldblooded trotter stallions.

“It is unlikely to be feasible in large screening studies, and once a genetic test for osteochondrosis becomes available, clinical differentiation of septic and aseptic lesions is superfluous.”

They said that, given the results, it was highly likely that the difference found was due to bacterial infections.

Prevalence of osteochondral lesions in the fetlock and hock joints of Standardbred horses that survived bacterial infection before 6 months of age
Eli H. S. Hendrickson, Sigrid Lykkjen, Nils I. Dolvik and Kristin Olstad
BMC Veterinary Research 2018 14:390

The study, published under a Creative Commons License, can be read here.

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