Venograms and Laminitis

Q. - What is a venogram and how is it used to help diagnose laminitis?

A. - In an X ray we can see the coffin bone and other bony structures within the foot capsule, but we can’t really get a good look at the soft-tissue structures, including ligaments and vessels. A venogram is also an X ray, but we place a tourniquet on the leg inject a dye into the vein that feeds the foot. That dye moves into the structures of the foot around the coffin bone and the vessels that feed the laminae (blood flow to the laminae is compromised during laminitis) and, in the image, shows up bright white. It can give us an indication of where there’s leakage of blood in the hoof capsule or maybe limited blood supply.

Ringbone Treatment Options

Q. - What’s the best way to treat ringbone?

A. - Ringbone is proliferation of bone around the pastern or coffin joint. It has often been classified as articular when the joint is involved, or nonarticular when it is outside the joint. It can, however, have both an articular and nonarticular component.

Ringbone can be a frustrating disease that is progressive, much like knee pain and back pain in people.

I don’t know that there’s an ultimate cure or prevention, if you will. My feeling is if we start treating some of these horses earlier when we have only slight to mild problems, we may be able to slow down the progression. Things like Surpass (a topical anti-inflammatory cream), shock wave therapy, treating the joint if the joint is actually involved—all of those things decrease inflammation and we have to assume will probably decrease the progression of the disease. Nobody has studied that specifically, but those would be the things, short-term, that I would probably do when a horse has a flare-up in that area.

Ultimately, if it’s causing performance-limiting problems and it’s the pastern joint, we can fuse the pastern joint. Once the motion stops, the pain stops, and it’s a relatively high success rate, 60-80% depending on if it’s front or hind leg. Those horses go back to full work. It’s expensive (it usually costs about $5,000 for the surgery) and the layup time is six months to a year, so it’s not a fast procedure. But at least there’s something that we can do.

If it’s ringbone in the coffin joint, there’s not really a whole lot we can do, and that certainly frustrates all of us.

Rattlesnake Bite Vaccine

Q. - I have questions about a vaccine for snakebites: My own veterinarian has not mentioned this but my neighbors vet recommended that they vaccinate their horses against rattlesnake venom. Last summer six horses in two-mile radius of our farm sustained snakebites, and I am trying to anticipate the upcoming season. I was told by my neighbors the vaccine is a series of three injections, and often horses develop a temporary swelling or irritation at the injection site. Can you tell me more about this vaccine? Is it effective against all rattlesnake species in the United States? Is a horse that previously has been bitten by a rattlesnake more or less likely to have a severe reaction if bitten again?

A. - There is, indeed, a rattlesnake vaccine labelled for horses. And I must disclose that I have done collaborative research work with the company that produces the vaccine, Red Rock Biologics. The rattlesnake vaccine is made with venom from the Western Diamondback Rattlesnake, and in vitro studies showed it to be effective in neutralizing this snake’s venom. We know that rattlesnake venoms, while different in many ways, are also similar in many ways and contain many similar toxins. This knowledge would lead one to believe that antibodies made against one rattlesnake venom may be at least partially effective at neutralizing other rattlesnake venoms. Scientific studies have shown that some rattlesnake venoms are more similar than others; however, a vaccine against any one venom would not likely provide protection against all rattlesnake venoms in the United States or elsewhere. So, the answer to your second question is that it is unlikely that antibodies produced from vaccination with the (Western Diamondback) rattlesnake vaccine would be fully protective against every species of rattlesnake in the United States. To my knowledge, studies of this type have not been done.

The initial vaccine series is a series of three injections given in the muscle 30 days apart. There are not specific instructions for administration location of the vaccine, but any of the usual sites for an intramuscular injection would be acceptable, including the neck or low in the semimembranosus/semitendinosus muscles (hamstring area).

I participated in the safety trial for the vaccine, and we only had a couple of horses develop injection site reactions that were very mild and resolved without any treatment.

The timing of the vaccine, in my opinion, should be such that the horse will have the highest antibody titer during the peak rattlesnake season, which may vary depending on the area of the country where you reside. This means that horses would need to receive all three vaccines prior to the beginning of rattlesnake season, with the last one being at least 10 days prior to rattlesnake season.

Your question about previously bitten horses is very good and one that does not have an exact answer. I can only provide an answer in relation to what we know in other species. From my research we know that horses do develop antibody titers against rattlesnake venom after being bitten by a rattlesnake, but we do not know how long these antibodies last or if they are protective if the horse is bitten again. People that are bitten by poisonous snakes multiple times tend to have weaker reactions each subsequent time they are bitten. When I was in private practice I treated dogs and horses bitten by rattlesnakes, and animals that were bitten more than once seemed to have weaker reactions with each subsequent bite; however, I do not have enough data currently to prove this.

The rattlesnake vaccine is rather new in the horse, and I do not believe there are any published studies as of this moment; however, we have submitted a paper on the comparison of antibody titers in naturally bitten horses with vaccinated horses.

Preventing Gastric Ulcers

Q. - What is the best way to prevent gastric ulcers in horses? I know there are various treatments available for horses that have been diagnosed with ulcers, but can horse owners in general prevent ulcers, and what is the best method in that regard? My understanding is that I should offer my horse:

1. Free access to grazing if possible;
2. Free access to hay with little to no fasting, if stabled for long periods;
3. Alfalfa/alfalfa chaff fed with hard feeds; and
4. Minimal disruption to his routine.

Perhaps you can confirm or elaborate on these?

A. - Gastric ulcers can affect upwards of two-thirds of all performance horses and can cause weight loss, colic, and poor performance. Ulcerogenic factors identified include low-forage diets, intense/increased exercise, high-concentrate diets, regular/prolonged transport, feeding at intervals, management/housing changes, water deprivation, weaning, moving to a new home, and prolonged stabling. Prevention is therefore key to keeping your horse healthy and at the top of his game. The most effective prevention strategy involves a comprehensive combination of feeding, management, and pharmacologic approaches.

By understanding the physiology of horses’ gastrointestinal systems, we can feed them in a manner that reduces their likelihood of developing gastrointestinal problems including gastric ulcers. Horses are by nature continuous grazers that eat coarse grasses 16 to 18 hours a day in natural settings. However, many performance horses have significantly restricted grazing access and often require additional caloric supplementation to meet their energy requirements.

This predisposes these horses to ulcer development. Feeding strategies veterinarians recommend to decrease ulcer incidence include allowing free access to or long periods of grazing; providing constant hay access during periods of confinement longer than six hours; using restrictor/slow feeders to promote “foraging” and saliva production; feeding frequent small grain concentrate meals; replacing simple carbohydrate calories with fats and fiber-based diets; offering alfalfa hay/cubes/pellets; and providing continual access to clean, fresh water. Of these feeding practices, maximizing consistent daytime fiber intake and providing free water access are the most important.

When used as part of a comprehensive approach, some oral supplements might be beneficial when administered longterm. Administration recommendations are directed at maximizing their effect (for example, when they are fed relative to known periods of gastric hyperacidity), but the scientific evidence of their efficacy is sparse, so ask manufacturers for published evidence before purchasing.

Minimizing stress relative to housing, common routines, and transport may also be beneficial. Horses housed permanently on pasture with light exercise are six times less likely to get ulcers than stalled, moderately exercising horses, and horses with constant access to forage are four times less likely to get ulcers.

Minimizing changes in routine and applying stereotypy-reducing strategies—particularly in young horses—may be beneficial, as these behaviors’ development is often associated with ulcers. Researchers have shown that installing mirrors in stalls and trailers can help reduce blood cortisol (stress hormone) levels and potentially lower ulcerogenesis.

Although these feeding and management changes can result in lowered ulcer incidences overall, these practices often cannot overcome the isolated, high-stress, ulcerogenic nature of showing/competing. Many horses in these circumstances benefit from pharmacologic acid reduction prior to and during competition. Owners can administer UlcerGard (omeprazole), the only FDA-approved and scientifically proven ulcer prevention medication in horses, as a once-a-day dose just prior to and during stressful events. Other unapproved medications (i.e., ranitidine) are used with varying success in treating ulcers—often combined with decreases in training/stress—but researchers have not extensively studied doses, dosing intervals, and length of administration for prevention.

The important thing to remember is that not all horses are the same, and they might respond differently to the recommended approaches. Consult your veterinarian when instituting comprehensive feeding, management, and medication programs to maximize your success and to help avoid any unforeseen complications.