Laminitis in Performance Horses

Although obese ponies are the most likely candidates for this crippling disease, racehorses and performance horses are not immune to developing this condition due to the high-energy rations they need to consume to achieve optimum performance.

Performance horses may suffer a sudden, severe attack of laminitis that may end their athletic career or more commonly, a low-grade or “sub-clinical” form of the disease that may significantly impair performance without causing obvious or severe lameness.

Laminitis – A hidden danger

Research has proven that the subtle signs of laminitis may be missed unless x-rays of the pedal bones (coffin bone, P3) are performed. 

Up to 46% of apparently sound thoroughbreds in full race training may show one or more radiographic signs of laminitis¹, including:

• Slight rotation of the pedal bone
• Resorption of bone from the bottom of the pedal bone (pedal osteitis)
• New bone formation along the front of the pedal bone, and
• A slightly dished appearance to the hoof wall

Furthermore, racing thoroughbreds with radiographic evidence of low-grade laminitis with no lameness on veterinary examination, earn 66% less prize money per race than horses without radiographic changes associated with laminitis when measured over a six-month period¹.

These results strongly suggest that low-grade chronic laminitis is affecting racing performance despite horses showing no obvious clinical signs of the disease.

It has been suggested that this may be a reason why some horses have difficulty performing on hard tracks, but perform better on softer ground, although this is unproven.

It is thought that low-grade laminitis in performance horses is related to their consumption of high grain diets for long periods of time in order to meet their energy demands.

Indicators of low grade laminitis

The subtle signs of lameness associated with laminitis in the performance horse can be difficult to identify.

The performance horse may show no obvious signs of lameness, with poor performance being the only difference from their healthy stable mates.

However, in slightly more severe cases there can be “tell-tale” warning signs that suggest low-grade laminitis. These signs include the following:

• “Jarred-up” or “sore feet” in the front hooves, particularly when worked on hard tracks
• A short, scratchy gait which does not warm out, and worsens after fast or hard work – (some may wrongly assume that horse appears sore in the shoulders)
• Prominent “growth rings” on the hoof wall
• A “dished” hoof wall with flared out toes (often with low compacted heels)
• Broken away hoof edges and flaky soles – soles may appear flat or “dropped”
• A crumbly white line or low grade “seedy toe”
• Pain when hoof testers are applied around the edges of the sole, particularly in the toe region.
• Sore footedness after hoof trimming or shoeing
• Toe cracks

Research in Australia has shown an association between high grain diets, hindgut acidosis (high levels of acid in the large bowel) and symptoms of low-grade laminitis.

Hindgut acidosis can also cause other side effects in addition to hoof disorders including loose “cow-pat” droppings, sour-smelling droppings and nervy, fizzy behaviour and other behavioural changes such as stall licking and wood chewing².

References

1. Linford R, O’Brien T & Trout D (1993) Qualitative and morphometric radiographic findings in the distal phalanx and digital soft tissues of sound thoroughbred racehorses. American J. Vet Research 54:1, 38-51.
2. Johnson KG, Tyrrell J, Rowe JB & Pethick DW. (1998) Behavioural changes in stabled horses given non-therapeutic levels of virginiamycin. Equine vet. J. 30:2, 139-143.