Laminitis is one of the most common causes of lameness and disability of horses and ponies. It is a disease associated with ischaemia of digital dermal tissues, it is not primarily an inflammatory disease; hence laminitis is a misnomer. The bond between the dermal and epidermal laminae (the inter-laminar bond) is the only means of support of the distal phalanx within the hoof. If sufficient inter-laminar bonds are destroyed the animal becomes foundered ie; the pedal bone moves distally within the hoof. The cause of laminitis is unknown; the following situations are known to frequently precede an attack of laminitis. Animals in these situations can thus be regarded as at high risk from laminitis. These situations may occur singly or in combination. 1. Obesity / Overeating. Many animals perform no work and are used as garden ornaments by people with limited understanding of horse management. Horse owners are encouraged to overfeed their animals by feed companies, show judges and peer pressure. 2. Toxaemia. Any systemic disease involving a septic or toxic focus i.e., pneumonia, pleurisy, diarrhoea, colic (particularly following colic surgery), purulent metritis. Effective treatment of the initiating cause must be accomplished before improvement in the laminitis can be expected. Bacterial, viral, plant, chemical, and fungal toxins have been implicated. 3. Trauma / Mechanical. Fast or prolonged work on hard surfaces i.e., jumping ponies in summer, racehorses on firm ground, inadequately fit endurance horses are at high risk. 4. Hormonal. Some laminitis cases appear to be hypothyroid although the indiscriminate use of thyroxine supplementation without testing is not recommended. Elderly animals often develop neoplasia of the pars intermedia of the pituitary gland. This manifests as a failure to shed the hair coat in the spring, the coat becomes long and fine or matted. The animals are often polydipsic and may be diabetic. Laminitis is a common sequel to such tumours. Measurement of T3, T4, insulin and cortisol following injection of thyroid releasing hormone is a useful test for both thyroid function and pituitary neoplasia. 6. Stress. Any stress such as overworking unfit horses, prolonged travelling in hot (or cold) conditions, anthelmintic treatments (particularly double doses of pyrantel) or vaccination may result in laminitis in some animals. Certain cream treatments for the treatment of sarcoids seem to be related to the onset of laminitis and founder.
