Laminitis in the Pony and Horse

Laminitis in the Pony and Horse

Imagine you have finger nails which grow all the way around the end of your finger rather than just on the upper surface. Then, imagine the finger nail being part torn from its bed and having to walk on it at the same time. This is the pain a horse feels with laminitis. Still drawing the comparison with finger nails, look at your own nails and see the fine striations growing towards their tips. These are the 'laminae'. Laminitis is inflammation of the laminae and can be caused by a range of different conditions.

Laminitis of dietary origin is the principal cause of laminitis in our ponies and horses in Guernsey. The animals most prone to this condition are those of 'native breeding', over-weight and under-exercised with excessive access to food. The access to food beyond the horses normal requirements is an influencing factor to the induction of laminitis.

Factors which interested us, as veterinarians, was that although we saw an increased incident when the spring and early summer grass suddenly sprouted, we were also seeing cases at other times of the year including at times, in the winter. The production of 'richer' grass was not in itself a sufficient answer. Initially it was believed that high protein content was the causative factor but in recent years it has become evident that it is the presence of a nutrient group called soluble complex carbohydrates which pass to the hind gut of the horse and cause a massive change in the balance of the digestive bacteria of this area. Large amounts of lactate producing bacteria develop under these conditions and produce exotoxins which release enzymes from the basement membrane of the horses hoof laminae causing inflammation and separation of the hoof from the live dermal laminae. These complex carbohydrates are present in rich grass and particularly so in cereals (hence, laminitis after raiding the food bins) but also are present when pasture is 'stressed' such as after fertilizing, a hard frost or sudden change in climatic conditions.

There is also vasoconstriction (closing down) of the capillaries in the hoof causing poor circulation and congestion. This explains why horses with laminitis have hot feet and a marked digital pulse.

Other causes of laminitis are too numerous to mention.

-In the middle aged to older pony a laminitis caused by a cortisone imbalance known as Cushings syndrome is being diagnosed more frequently. This is caused by a benign tumour of the pituitary gland of the brain, in most cases. Treatment is available to improve and stabilize the condition.

Any acute illness with sudden, high, temperature.

Excessive exercise on hard, concussive surfaces.

Poor farriery with hooves cut too short or unbalanced.

Production of internal toxins from kidney or liver disease or retention of the afterbirth in recently foaled mares.

Sudden and major changes in hoof temperature, sucha s might occur under severe winter conditions.