Normal HL values vary by breed and age:Weanlings will have a greater proximal HL compared to distal HL
Yearlings will have approximately equal proximal and distal HL
Thoroughbreds are usually 17mm proximally, and 19mm distally
Standardbreds have been shown to have a similar proximal and distal HL, around 16 mm at 2 years old, and 20 mm at 4 years old
Warmbloods have similar proximal and distal values, up to 20 mm each
HL tends to increase with age, up to 17 mm in most light breeds, or higher, especially in very old animalsVenogramsVenograms can help determine the prognosis for the animal, particularly in horses where the degree of pain does not match the radiographic changes. In venography, a contrast agent, visible on radiographs, is injected into the palmar digital vein to delineate the vasculature of the foot. The venogram can assess the severity and location of tissue compromise and monitor effectiveness of the current therapy. Compression of veins within the hoof will be seen as sections that do not contain contrast material. Poor or improper blood flow to different regions of the hoof help determine the severity of the laminitic episode. Venography is especially useful for early detection of support limb laminitis, as changes will be seen on venograph (and MRI) within 1–2 weeks, whereas clinical signs and radiographic changes do not manifest until 4–6 weeks.Horses undergoing venography have plain radiographs taken beforehand to allow for comparison. The feet are blocked to allow the sedated horse to stand comfortably during the procedure.
Mechanical separation
Commonly known as road founder, mechanical separation occurs when horses with long toes are worked extensively on hard ground. The long toes and hard ground together contribute to delayed breakover, hence mechanical separation of the laminae at the toe. Historically, this was seen in carriage horses bred for heavy bodies and long, slim legs with relatively small hooves; their hooves were trimmed for long toes (to make them lift their feet higher, enhancing their stylish "action"), and they were worked at speed on hard roads. Road founder is also seen in overweight animals, particularly when hooves are allowed to grow long; classic examples are ponies on pasture board in spring, and pregnant mares. Poor blood circulation
Normal blood circulation in the lower limbs of a horse depends in part on the horse moving about. Lack of sufficient movement, alone or in combination with other factors, can cause stagnant anoxia, which in turn can cause laminitis.A horse favoring an injured leg will both severely limit its movement and place greater weight on the other legs. This sometimes leads to static laminitis, particularly if the animal is confined in a stall. A notable example is the 2006 Kentucky Derby winner Barbaro.Transport laminitis sometimes occurs in horses confined in a trailer or other  transportation for long periods of time. Historically, the most extreme instances were of horses shipped overseas on sailing ships.