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Laminitis in performance horses

Laminitis does not only occur in overweight ponies grazing on lush pasture!

Although obese ponies are certainly likely candidates for this crippling disease, racing horses and performance horses are also at risk of developing the 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 (the hoof bones) 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
  • 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.

comparison of average earnings per race

These results strongly suggest that low-grade laminitis is affecting racing performance without the horses showing any obvious symptoms 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.

The cause of low-grade laminitis has not been determined. However, as performance horses, usually receive high grain diets for long periods of time in order to meet their energy demands, the chances are high that the laminitis may be feed-related.

Indicators of low grade laminitis

Performance horses may show no obvious signs of lameness, with poorer 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 – the horse may also appear 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

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.

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