Laminitis

As a young horseman, I was taught by those with more experience to look upon the emerald pastures of April and May with dread. “Don’t turn your pony out on that grass or he’ll founder,” they would warn me. I didn’t know what founder was but it sounded bad. I got the impression that it mainly consisted of a hard crest of the neck followed by death. I was slightly misinformed, as are many people concerning this mysterious condition.

Founder is a layman’s term for laminitis, or inflammation of the soft tissue structures in the foot. I think of founder as a particularly severe episode of laminitis where the third phalanx, or “coffin bone,” separates from the surrounding soft tissue and sinks toward the sole of the foot, just as a foundering ship sinks to the bottom of the sea. Fortunately this is a rare event, though laminitis is a common disease.

Many experienced horse people think of the classic foundered equine as a fat little Shetland pony. This stereotype is slightly misleading. I see many ponies with laminitis, but I see more full-sized horses. The majority of them are obese (this is where the cresty neck part of the picture comes in: a horse’s crest is composed largely of fat). The exact reason that obesity is associated with laminitis is unclear, but these horses probably have dietary habits and metabolic problems that predispose them to laminitis. I have seen laminitis in physically fit horses that experienced sudden changes in diet, unusually hard work, other sicknesses (severe diarrhea, for example), or injuries.

Laminitis is associated with spring. This is due to the rapid growth of grass in this season. The growing grass plant goes through rapid changes in sugar content. This amounts to a dietary change for your horse, even if you did nothing to change the amount of grain, hay, and supplements in the ration. In Virginia, we can have spring-like conditions for much of the year, so we see laminitis commonly in spring and fall, and during the occasional cool, wet summers. Why does a dietary change cause laminitis? No one is certain, but we think it might involve sudden changes in the bacterial population in the horse’s guts, and toxins that are released as some types of bacteria die off in response to the changing chemical composition of the grass. A similar change can occur if your horse suddenly consumes too much grain.

A horse with laminitis has painful feet. Symptoms include reluctance to walk, especially over hard ground and gravel; reluctance to turn in a tight circle; standing with the legs placed unusually far forward, the rear legs under the belly; hot feet; and thumping pulses in the arteries leading to the feet. All four feet are usually affected, but the front feet are more painful because they carry more of the weight. If your horse is only lame in one foot it’s probably not laminitis; however if he is extremely lame for a long time he may get laminitis in the good foot from bearing all his weight on it all the time.

If you see symptoms of laminitis there are several things you can do while you are waiting for the vet. Place your horse on a soft surface. Several inches of sand is the very best, but any soft ground or deep bedding (6 inches or more) will help. If your horse is really painful, give one 1 gram tablet of bute (phenylbutazone). Bute is an anti-inflammatory, and most research is showing that anti-inflammatory therapy is the most important medicine for treating laminitis. If bute is unavailable one could also use flunixin (Banamine) or large animal aspirin boluses. Running cool water over the feet may be helpful too.

Preventing laminitis is possible. Limit grazing when the grass is growing fast. Use a grazing muzzle if your horse is too piggy. Turnout in a round pen or arena for exercise, instead of on pasture, is another option. Feed reasonable amounts of grain. Most horses get more than they need. Horses that are not in work or only in light work can do well on a ration of free-choice good quality hay and/or pasture alone. Proper and timely foot trimming is critical. Long toes add stress to the foot and act as a lever, pushing the hoof capsule away from the coffin bone. Maintain a good general health plan including parasite control, vaccinations, and dental care.

Pastern Dermatitis

This is a common skin condition during wet weather and when dew is heavy on the grass. It is often called scratches, mud fever, and dew poisoning. Mild cases look like rain rot on the lower legs. The scabs are often sensitive. If the infection goes deeper and causes an allergic reaction, the legs may swell. In such cases, the horses can be very lame.

It is difficult to prevent this problem in sensitive horses on pasture. Ideally they are kept inside until the sun dries the pasture. Dry lots and arenas can also be used to avoid wet conditions.

Mild, superficial cases of scratches can be treated topically by cleansing with betadine shampoo (allow the suds to remain on the skin for 15-20 minutes), removing the scabs (a studded rubber mitten helps), drying, and applying a 1:1 mix of zinc oxide (Desitin) with nitrofurazone (Furazone ointment, the flourescent yellow stuff). If this does not help after a few days, or if the legs are swollen and sore, you should have a vet take a look.

Mosquito–Borne Encephalitis

As mosquito season approaches we are braced for neurological viral infections. The diseases we see in this area are Eastern Equine Encephalitis (EEE) and West Nile virus (WNV) infection. Most of you are very educated about WNV due to the recent epidemic and media attention. During the summers of 2002 and 2003 we had a large number of cases in Virginia and Dr. Massie and I became all too familiar with treating the disease. The summer of 2004 was much better, and in 2005 there were no cases of West Nile reported in Virginia. This appears to be due to a combination of factors:

1. Widespread vaccination has built up the immunity of the general population.

1. Natural exposure to the virus either killed the most susceptible horses or induced strong natural immunity.

1. Many of the birds that served as the reservoir for this virus were killed by the infection, so the pool of carriers was reduced.

It appears that the risk of WNV infection is decreasing but it is too early to tell if it is reduced to a level that eliminates the need for vaccination. The American Association of Equine Practitioners still recommends annual vaccination against WNV, with boosters in the late summer and fall in areas where mosquitoes are found late in the year.

Eastern Equine Encephalitis

This disease is spread from birds to horses (and humans) by mosquitoes. We do not see a large number of cases, but the reported number has recently increased in Virginia. This may be due to complacency brought on by the relatively low rate of infection, and the large amount of press given to WNV and, more recently, EHV-1 encephalitis. This disease is different from WNV in that it is native to this area and is not as lethal to birds. It is more fatal in horses than WNV. It might be more likely for this illness to persist in our area than WNV. Annual springtime vaccination is considered very effective in controlling it.

Equine Herpes Virus

This virus is currently receiving a huge amount of attention. Multiple outbreaks of neurological EHV-1 on eastern racetracks and boarding stables have occurred this year. Racing has been disrupted as several tracks were placed under quarantine.

Historically a concern to pregnant mares (abortions) and young horses (respiratory problems), EHV-1 seems to have become more dangerous in recent years. Affected horses have a high fever and depression, quickly followed by weakness in the legs and difficulty emptying the bladder. This can be followed by inability to stand and death within 4-5 days. It is highly contagious and spreads by casual direct contact and indirectly on feed and water buckets, and even on the hands of caretakers. Horses that contract the virus and recover will remain carriers for life, shedding the virus occasionally when stressed.

No vaccines are very effective against this neurological strain of herpes. Even natural infection only induces 6-9 months of immunity. Horses exposed to transient equine populations (boarding facilities, tracks, stabled at show grounds etc.) may be partially protected by vaccination every 3-4 months. Vaccinating more often than that may be harmful. Backyard horses and small closed herds have minimal risk of exposure. If you have horses that travel and come into close contact with other horses you should isolate them for at least three weeks before rejoining the herd. This is a good biosecurity rule in general, not just for EHV.