- Cushing’s Disease – a malfunction of the pituitary gland, leading to excess production of cortisol, which is a natural steroid. This is a typical problem of the older horse.
- EMS – Equine Metabolic Syndrome caused by obesity, especially in ponies. It causes imbalances in blood sugar/fat/insulin ratios, which result in insulin resistance and lead to laminitis.
- Undigested sugars and starches passing into the hind-gut of the horse.
- Percussion – the effect of riding/jumping on hard ground.
- Use of steroids – thought to make the gut wall more permeable to the toxins which trigger laminitis.
- Infection – e.g. post-parturition.
- Antibiotics can upset the balance of the hind-gut microflora.
Laminitis is frequently caused by undigested sugars and starches passing into the hind-gut of the horse, where they are broken down by bacteria to lactic acid. This increases the acidity in the hind-gut, suppressing the fibre-digesting bacteria. Other species (Streptococcus, Salmonella, E. Coli etc) proliferate. It is thought that they produce toxins which pass into the bloodstream. When they reach the hooves, these toxins trigger laminitis.
Fast-growing lush grass produces large amounts of sugars, especially on bright sunny days. Unused sugars are stored as fructans, especially if the grass is stressed because of cold or drought. Fructans are very sweet, and make grass extremely palatable. They cannot be digested in the horse’s small intestine and so pass into the hind-gut where they are readily broken down to lactic acid. Susceptible horses should ideally graze at night and only be allowed hay or straw during the day. Grazing muzzles can also be helpful.
Horses have traditionally been fed on starchy products such as oats, barley, maize, etc. Many modern proprietary feeds also have a substantial starch and sugar content. Some horses, and more especially ponies, are unable to cope, especially if they have managed to raid the feed-store. The consequent hind-gut overload may trigger laminitis or colic.
By combining feeds with long fibre such as chopped straw or alfalfa it is possible to slow the rate of passage of feed through the small intestine and so ensure maximum digestion of the soluble nutrients. Replacing starchy ingredients with high quality vegetable oils and proteins, and good quality digestible fibre greatly reduces the likelihood of excess starch and sugar reaching the hind-gut. Probiotic supplements or yeast can boost the beneficial bacteria in the hind-gut, and inhibit colonisation by harmful species.