Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Aorto-Iliac Thrombosis

Synonyms: Aorto-iliacofemoral Thrombosis, Thromboembolism

Post-Exercise Trembling & Treading, Aorto-iliac Thromboembolism


The descending aorta is a huge artery (larger than a garden hose) that courses along the roof of the rear part of the abdomen. As it reaches the roof of the pelvis, it divides into several large right and left branches that carry blood to each limb. In this uncommon and poorly understood condition, a large clot develops near this branching region. It may occlude blood flow to one of both hind limbs. This results in the reduction of circulation to one or both hind limbs.

The signs are variable lameness and changing lameness that may become severe but can be difficult to localize in a lameness exam. The classic gait abnormality comes on when the horse is exercised.

The cause of aorto-iliac thrombosis is thought to be parasitic damage to blood vessels. There are likely genetic factors as well.

In many cases, the affected limb will be cooler than the unaffected limbs. In some cases, a veterinarian may be able to detect the clot on rectal palpation and, using ultrasound, detect the clot in one of the large ileal arteries within the pelvis.

Diagnosis is through clinical examination and ultrasound.

Treatment may be conservative or surgical.

my vet's role


The prognosis is guarded with treatment and controlled exercise. The condition is thought to be more common in geldings and horses with a history of intense exercise.

It is thought that consistent exercise may favor the development of new circulation to the limb.

my role

Questions To Ask Your Vet:
  • What treatments are available to reduce or remove the clot?
  • What are the success rates with various treatment options?
  • If the condition is successfully treated, what is the likelihood of recurrence?

The only rational step for prevention is maintenance of a good parasite control program, guided by your veterinarian.

Author: Doug Thal DVM Dipl. ABVP