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Puzzling Condition Still Misunderstood In Horses

Updated: Mar 13, 2023

Aorto-iliac thrombosis is still one of the most poorly understood conditions in the horse. Basically the problem is one in which there is deposition of debris along the major arteries supplying blood to the hind legs. As the debris collects in the arteries the space in the vessel through which the blood flows becomes increasingly smaller thereby allowing less and less blood to flow through it.

A horse which is performing requires a tremendous amount of blood to power the muscles of the legs. If you diminish the flow, then you decrease the performance capability of the animal. Horses with aorto-iliac thrombosis will simply not race/perform up to par. They may demonstrate a gait in which the animal seems to be almost unbalanced behind. On examining the animal after a race/event, the hind legs may be cooler than normal. If there is not enough blood circulating in the limbs, then there is not enough blood present to even keep the legs warm. Performing a test in which the vein on the inside of the hind leg is blocked and then allowed to fill up with blood may demonstrate that the time required for the vein to fill is far longer than normal.

Some affected animals after racing/event may demonstrate distinct discomfort in the hind legs. These horses will tend to be continuously shuffling their hind legs such that no leg remains on the ground for longer than a few seconds. Think of it in this fashion. If you held your foot still for long enough then eventually it would 'go to sleep.' This simply means that there is very little blood circulating in the area. As you move your foot around again, more blood would flow into the area. At this time you would experience a 'pins and needles' effect. This effect is exactly what the horse would feel and hence his apparent discomfort.

For a long time it was felt the condition was due to migrating bloodworms causing blockages in the arteries. The horses were therefore treated with very high doses of worm medicine. Some animals did indeed respond to the treatment and therefore it is likely worth attempting on any affected animal. Today the condition is felt to be similar to if not the same as arteriosclerosis in man. Research in that direction will likely result in a definitive treatment for the condition.

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