The diet of laminitic horses must be chosen very carefully, this is because laminitis often originates in the gut then causes severe problems in the hoof.
Caecal bacteria from horses adapted to grain diets are less efficient than those adapted to hay. If a hay-adapted horses is suddenly put on a grain diet, impactions may occur, laminitis, colic or swollen legs may then occur. There have been a number of causes associated with laminitis (Frape, 2009);-
- Fat ponies on lush pasture
- Carbohydrate overload
- Excessive weight bearing on a sound leg and post- exhaustion myopathy
- Stress from exercise in overweight animals
- Excessive tube feeding of sick, aphagic horses with a high carbohydrate-protein diet
The pie chart below shows how the main cause for the onset of laminitis is lush pasture, this is due to it containing fructans which are rapidly fermented in the hindgut. Grain overload was also the cause in 7% of cases, this shows how feeding has a large effect on laminitis (King, 2004). However, the true causes of laminitis are still unknown; this is why there are a lot speculations and theories into this area.
Pie chart to show the causes of laminitis (Image from Lameness and Laminitis in U.S Horses, King 2004).
There are a number of theories that try to explain the causes of laminitis.
The levels of microorganisms in the gut change depending on what the horse is fed. Therefore a change in the ratio of concentrates to forage being given the horse can result in a problem. High fibre diets are the best for horses so making sure that horses that may be prone to laminitis get a high fibre diet is very important. Giving the horse excessive quantities of starch from cereals or fructans from pasture can cause incomplete pre-ileal digestion and absorption of carbohydrate. The material that has not been digested in the small intestine will undergo rapid fermentation in the large intestine. There will be a large amount of volatile fatty acids produced causing a fall in pH. The environment will then be more suited to the microbes who produce lactic acid causing it to accumulate leading the pH to decrease even further. Endotoxins will then be released which will go into the blood (Frape, 2009).
The vascular theory is the oldest, this was developed by Hood (1999). This is when there are endotoxins in the blood which cause microthrombi and thrombosis. There is an increased blood flow to the foot but this is caused by the blood is diverted away from the laminae. The laminae is the part between the hoof wall and the coffin bone and has a vital role in hoof strength. Eventually there will be a degeneration of the bond between the hoof and the pedal bone which then sinks and rotates due to the horse's weight causing a chronic case. Laminitis is a local manifestation of a chronic problem. The front feet are usually the most effected. It also leads to the hoof growing much more rapidly and rings will appear on the hoof due to pressure being put on the coronary band (Frape, 2009).
Pasture management can also help to prevent laminitis. Grass should be kept short and leafy either by grazing or mowing and the soil should be appropriate. Restricting grazing early in the morning will avoid intakes of the highest concentrations of the bad carbohydrates encountered during the days. Horses can also wear a muzzle to restrict their intake of grass. Animals on a restricted intake of grass should be fed alternative sources of forage to make sure they get enough nutrients.
It seems there are many different factors leading to laminitis. Research seems to suggest the same causes are often seen. It is also thought there may be a number of contributing factors. Knowledge when feeding is important, however, research is sometimes conflicting and this will not always prevent laminitis as there may be other factors involved.