Biting and Snapping Pony

Q. We've been raising a Welsh pony for the kids.  At about nine months of age, he started with constant nipping at your arm and the lead shank, kind of playing with you.  We read on the Internet that this biting is a "colt thing," and that it should go away with maturity. Our vet thought that gelding him as soon as possible would help.  After he was castrated, the incessant nipping and playing pretty much stopped, but he then started less frequent but more serious biting.  When you were leading him, he would make a quick turn of his head and bite your forearm, usually just your sleeve.  After he put a big welt on my daughter's wrist right through her winter jacket, we decided to start punishing him by whacking him on the lips each time he did that. He tested each of us, but once we all had had a chance to let him know he couldn't do that, he hasn't really tried anymore. He has never gone back to the nipping and playing with the lead shank.

But now he has two new problems. One problem is that he has become pretty head shy--it's like he's got his eye on you all the time and can't seem to relax when you are leading him or working around his head. He holds his head high and cocked sideways, looking down at you like he's always afraid of being hit.  The second new problem is that he has a completely different type of attack. Every once in a while when you go to get him in the stall or pasture, for no apparent reason, he just lunges with his mouth wide open straight for your arm or shoulder. It's just one quick snap of his jaws on whatever he contacts. If he misses you, it could be the wall or the gate that he bites, or he might just snap in mid-air.  After the one snap, he immediately retreats and quivers like he knows he was bad.  This morning he came at my shoulder, and when he backed off, he had the hood of my parka and a chunk of my hair hanging from his teeth. I was on my butt in the stall doorway.  He was cowering in the corner of the stall. I realize now that he is too dangerous for the kids.  Any ideas on where to go from here? He's two years old.

A. Let me begin by commenting that you are not alone either in the initial problem or with the apparent complications, where attempts to eliminate biting seem to lead to head shyness or increasingly dangerous behavior. In most horses, correcting biting is easy and quick, but for certain individuals it can be very challenging.  The head shyness and the quick attacks you describe mean that the pony has failed to get the message that it is only the biting that is bad.  As you said, he is confused about what caused the punishment and is afraid of people. Now that he is truly dangerous, it becomes difficult to relax and behave normally, let alone respond effectively to his misbehavior.

At this point, the savage attacking represents a serious safety threat that must be addressed immediately. I should mention that some horses, usually intact stallions, periodically attack people as if they are trying to kill the person.  These horses typically have no history of biting or any type of aggression toward people other than the sporadic savage attacks. Unlike with your pony, the savage attack is usually much more than a single lunge and bite.  The recommendation for a truly savage horse would be euthanasia or very specialized management (similar to management of stud bulls) in which people are never in direct physical contact with the horse. It is difficult to be sure your pony is not one of those rare savage horses, but my long-distance guess is that the attacks you describe likely represent fear-related behavior resulting from your attempts to correct his milder form of biting. If that is correct, then there is hope that the behavior can be corrected and that this pony can be a useful and safe companion animal.

At this point, I would recommend a trainer who is experienced and competent with rehabilitating this sort of case. It would be great if you could find someone who specifically appreciates pony personalities.  The trick now is to get the pony to feel completely safe with people and to understand that it is only biting that will result in punishment. Most successful trainers use a gentle, reassuring handling technique.  They use ample positive reinforcement for good behavior and very well-timed, judicious punishment for the biting.  After the well-timed punishment, they immediately relax and proceed.

It typically takes a couple of weeks or less for the pony to return to normal, dependably safe behavior. I have seen horses and ponies with very severe problems get the message within a few minutes of interaction with an expert.  The trainer might wish to take the pony to his/her facility for initial evaluation and retraining, then later work with you and the pony together.  There sometimes is an advantage to beginning the retraining in an environment that is new to the animal, and working with one or more expert handlers who are relatively consistent in their methods. Some trainers prefer to work with you and the pony in your home farm environment from the start.  This has the advantage that the pony and you learn together. It is very frustrating when the pony becomes a gentleman with the new trainer and returns to his old ways with you. It has been my experience that for the particular problem of biting, and especially for ponies, relapse is a lifelong concern. So, once the behavior has been corrected, you or anyone who ever works with the pony should handle him consistently in this regard.  This often is a challenge when the goal is to have a kid's pony.

On one hand, this might be an opportunity for your family to learn a lot of good horsemanship. On the other, it might be wise to find a pony without the biting tendency and history for your family project.

Why Can I See the Whites of My Horses Eyes?

Q. - Why can I see the whites of my horse’s eyes all the time, even when he’s relaxed? He is a chestnut Appendix Quarter Horse gelding.

A. - The "eye whites" you are describing is the white color of the conjunctiva, third eyelid, and sclera, tissues that surround the central, clear cornea of the eye.

There are several reasons that a horse may have more of this white area showing. The most common reason is simply less pigmentation or brown coloring. Lightly colored horses, such as Paints, Appaloosas, and some chestnut horses have less overall pigment in their skin, including the areas around the eyes. Without the pigment, the white areas are much more visible.

Generally, this lack of pigment has no health or vision affects; however, horses with less pigmentation are more susceptible to developing skin cancer or squamous cell carcinoma. Therefore, I advise that these horses be protected from direct sunlight using fly masks or similar protective devices.

If there’s a sudden or gradual development of increased eye white, this may indicate a problem.  A painful eye may have an elevated third eyelid, and an eye that has been damaged might become smaller than normal and show more scleral white. Therefore, if you notice a change in the eye regarding the amount of scleral white, I encourage a thorough examination of the eyes by your veterinarian. 

Obsessed with Salt

Q. ~ My new 2-year-old filly is obsessively licking and biting her salt block. She lives on a dry lot and gets high-quality orchard grass hay, a daily ration of commercial horse feed appropriate for her growth stage and size, and an omega-3 supplement. She also receives ample fresh water. Her current workload is very light and mostly includes basic handling rather than exercise. I haven't had blood work done on her. Should I be concerned about her licking and chewing the salt block? Does it suggest there's a problem with her diet or health, and can she hurt herself by taking in too much salt?

A. ~ This is a very common question. The good news is that sodium chloride, commonly known as salt, is water-soluble. As long as your filly has ample fresh water as you indicate, and she’s actually drinking enough, excess sodium will simply be excreted in the urine.

The National Research Council (2007) reports the maximum tolerable intake of sodium chloride to be at about 6% of total dietary intake, presuming adequate water intake. Assuming your filly matures at about 1,100 pounds and consumes 2-2.5% of her body weight in forage and feed per day, this equals just more than 1 ½ pounds of salt per day. Few horses consume anywhere near this much.

However, be aware that signs of salt toxicosis include colic, diarrhea, frequent urination, and general weakness. You should consult your veterinarian immediately if your horse exhibits any of these clinical signs.

Horses have a defined appetite for salt and will seek to consume sufficient amounts to meet their needs. Most commercial feeds do not contain sufficient salt to meet a horse’s daily needs, and salt content of forages is usually low as well. Thus, it is recommended to provide a salt block and water at all times.

There are many reasons why she may be obsessively licking and biting at her salt block, including boredom. When kept on dry lots, horses will often search for things to forage (or chew) on, from fence posts to salt blocks. If it is possible, you can try to spread out her hay ration into three to four feedings per day so that her “chew time” is spread out a little bit.

Is My Horse a Tick Magnet?

Q. I have two geldings, a dark bay and a chestnut, that were turned out together for about two months. When I brought them back to the barn, the dark bay was covered in what seemed like hundreds of deer ticks. The chestnut maybe had five ticks. Why would there be such a difference in tick numbers if they were in the same pasture?

A. There can be distinct differences in blood-feeding arthropods’ (such as ticks and horse flies) attraction to individual horses. Some differences are inborn among these bugs; others are acquired after previous feeding exposure. Researchers are still learning which factors are important and how to use this knowledge to produce better repellents and protective chemicals for humans, horses, and livestock.

The factors that attract these bloodfeeders vary with the pest. For example, vision is important to horse flies. They see a dark moving shape in the distance and fly toward it. As they get closer, their senses check for other attractions, such as warmth, carbon dioxide, or specific skin odors. Often, dark-colored animals are more susceptible to attack from biting flies than light ones in the same herd because they are easier to see.

Ticks have limited vision so they rely on other senses. Hungry ticks climb vegetation and wait for a passing host. Ground vibrations from animal movement or carbon dioxide indicate a host is approaching. In theory, all horses pastured in the same field should pick up similar numbers of ticks. But once on a horse, the ticks might stay and feed or reject the animal and drop off without a blood meal. Over time, ticks continue to accumulate on “acceptable” animals; few will stay on those that have some sort of resistance mechanism.

Animals’ responses or resistance mechanisms to tick bites appear to be a very important factor in whether ticks remain on an animal. Ticks inject dozens of chemicals as they feed. Animals with strong immune responses to these materials are not good hosts. Their physiological reactions interfere with the ticks’ ability to feed so the ticks drop off without engorging. Differences in skin chemistry or oiliness, or accessibility of capillaries also may interfere with the feeding process. In some cases, strong reactions that result in itching and irritation may increase grooming activity, which reduces tick numbers.

It’s clear that some animals are more attractive to blood-feeding pests than others.

Continued research may help to develop more effective pest control tactics. In the meantime, protection efforts (e.g., sprays, clearing brushy pasture areas, etc.) can be focused around susceptible animals.

Post-Expiration Date Dewormer Efficacy

Q. - Is dewormer still good after its expiration date?

A. - Like all medications, dewormers have a limited shelf life, which is determined through drug stability testing. The expiration date on the label is the latest date for which the manufacturer can guarantee full product potency.

In addition to the expiration date, equal consideration should be given to proper product storage. If the dewormer was stored outside the recommended temperature range listed on the label (i.e., in the tack room or horse trailer where it could have gotten too hot or too cold) its drug stability will be negatively impacted, as well.

If an improperly stored or expired dewormer is utilized, the horse will likely not receive a sufficient dose and the product will fail to adequately address the horse’s parasite infection. Under-dosing is one of many factors than can contribute to parasite resistance.

Bottom line: If you want to be sure your horse is getting what you pay for, store all medical products within the label recommendations and administer prior to the expiration date.

Common Parasite Eggs Found in Fecals

Q. - What species of parasites are identified in a fecal egg count test?

A. - It depends on who is doing the count and the type of procedure used. If we’re just doing a typical fecal egg count using a technique like the McMaster’s, which is a common method, we’re mostly looking at (small and large strongyle) eggs.

We can’t differentiate between the large and small strongyle eggs—all of the eggs look the same, although we know from research studies from over a number of years that well over 99% of the eggs we see in a fecal sample are from small strongyles.

With that said, there are other parasite eggs you can see in the feces less commonly, such as tapeworms. However, a horse can be infected with tapeworms and you still won’t see the eggs in a fecal. Also, commonly in young horses, roundworm eggs seen during the fecal exam. And then, of course, there are some other less common parasites that you will occasionally see eggs from.

The eggs of these different parasites all look different, so if the person doing the count is well qualified, he or she will be able to identify the different species present.

Encouraging Horses to Drink

Q. - How can I encourage my horse to drink?

A. - You can lead a horse to water, but you can't make him drink! Thirst is triggered by an increase in the sodium concentration of the blood. Because horses lose a great deal of sodium in their sweat, they may also lose some of their trigger for thirst. Offering electrolytes will help stabilize the horse's blood electrolyte levels and should help encourage him to drink.

Generally making sure the horse always has access to fresh, clean water helps. Sometimes masking the water with flavoring agents may help if you travel and have different water sources (that may make a finicky horse drink less). You can also offer water mixed in with hay, hay cubes, or other feeds to increase water intake.

Re-evaluating Therapeutic Shoeing

Q. - If a horse has been wearing therapeutic shoes long term but has started to have soundness issues after two years of going well, is there any point or situation you'd recommend going "back to basics" with a straight shoe or barefoot to evaluate and pinpoint the issue's root cause?

A. - Yes, this is often the case. Therapeutic shoes can outlive their usefulness. The shoeing prescription needs to be re-evaluated intermittently. Therapeutic shoeing changes the way the foot loads, and can eventually overload other areas of the foot and cause lameness.

Can Humans and Horses Transfer WNV to Each Other?

Q. - Can horses contract West Nile virus from humans, or humans from horses?

A. - While horses and humans can get West Nile virus (WNV) from the bite of mosquitos (that have previously bitten a WNV-infected bird), both horses and humans are what we refer to as dead-end hosts. That means that once the human or the horse becomes infected with the virus, as a general rule the virus doesn’t replicate at high enough levels in the bloodstream, which is called “viremia.” So horses and humans don’t get high enough viremia to subsequently infect a mosquito so that that mosquito could transfer the disease to another horse or human. The only way for a horse or human to get West Nile virus is through a mosquito bite.

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.

The Importance of Vaccination

Q. - Why are vaccines important for the health of our horses?

A. - Basically, vaccination is the administration of some antigenic material (a substance capable of inducing a specific immune response in the body by binding to a specific antibody; it can be a property of bacteria, viruses, other foreign proteins, or even host tissue cells) that is designed to stimulate the individual immune system to fight disease. So, in a sense, a vaccine is “priming” the immune system against a specific disease.

Vaccines can prevent, ameliorate, or lessen illness from a potential infection or infectious diseases, but the tricky part is vaccine selection and administration protocols; things of that nature can be complicated.

In a sense, vaccination is not “one size fits all.” These decisions are based on risk of exposure to the diseases, the consequence of a specific disease, the effectiveness of the product, and potential adverse effects. You really have to weigh the cost of the vaccination against the potential cost of the disease.

Something else to remember is that a vaccination program is really designed to protect a population, as well as the individual animal. Also, vaccination is not a remedy for poor management. So, proper management, parasite control, and biosecurity measures are also necessary (in addition to vaccination).

Apple Cider Vinegar for Horses

Q. - I have heard many differing opinions about the possible health benefits of feeding horses vinegar. Is vinegar good for horses to consume?

A. - Vinegar in small amounts is fine for horses. It helps acidify the urinary tract, which might be helpful for some horses prone to urinary tract stones.

I suggest no more than a cup a day and use raw apple cider vinegar with the “mother” in it. The mother (mycoderma aceti) is a culture of cellulose and acetic acid bacteria used to ferment cider or wine into vinegar. The mother will look cloudy at the bottom of the bottle and is an excellent source of live microbials.

Start by adding a tablespoon of the vinegar to the horse's feed twice daily. Gradually work toward 1/2 cup to each feeding (two feedings per day) for a total of one cup per day.

Older Creature Comforts

Q. - My senior horse is 30 this year. Overall, he's a healthy horse with minor issues (I have him on a pellet diet because of his teeth). My biggest concern is his mental happiness. As his body deteriorates, how can I keep him comfortable and happy?

A. - What a great question. I don't know of any research on changes in horses' mental comfort or what we might interpret as loss of happiness in horses of advanced age like we think of in some people of advanced age, so I can only answer from experience. It has been my impression that the behavior and "attitude" of healthy, physically and socially comfortable aged horses doesn't differ much from that of younger horses. Rather, their attitude generally reflects their physical health and comfort as well as their social and environmental comfort.

If your 30-year-old horse appears happy, I would not expect that to change until he develops a physical or social discomfort. If you think your horse is not as mentally comfortable at 30 as he was at 20 or 10, then I would recommend working with your veterinarian to try to figure out if anything physical or environmental is bothering him that could be alleviated. Unfortunately, many of agings inevitable aches and pains are not easily relieved long-term without side effects that can also be bothersome. And as horses age, they tend to lose some of their trusted herd-mates, and available new companions might not be equally compatible.

Old School Tying Up Treatment

Q. Your article on tying-up ("Exertional Rhabdomyolysis: Not Just Tying-Up Anymore"­) was very detailed but left out the old remedy I have used successfully every time: vitamin E/selenium injections prior to whatever led to tying-up episodes in the past. I never had this fail and wonder why it has been abandoned?

A. Results from studies done on Standardbreds that developed tying-up found that these horses had higher levels of vitamin E and selenium than horses that did not tie up. This led to the conclusion that tying-up was not consistently caused by a deficiency in these vitamins and minerals. In addition, newer formulations of vitamin E and selenium are more bioavailable (a greater amount is absorbed by and made available in the horse's body), so it's now possible to achieve adequate systemic levels by dietary supplementation (rather than injections).

Tumors and Treatments

The luster and shine of a horse's coat speaks volumes about his inner health. But problems might lurk beneath the skin in the form of tumors or other lumps. As you groom your horse, take extra care to notice any suspicious changes, as some skin lesions can pose troubling health consequences. The most common equine skin tumors to watch for are melanoma, squamous cell carcinoma (SCC), and sarcoids.

Melanoma

Horses' tumor susceptibility, especially for melanoma or SCC, correlates with the degree or lack of skin pigmentation. Researchers claim in studies that 75-80% of gray horses over the age of 15 eventually develop melanoma. However, the equine form of this skin tumor is not usually malignant or as rapidly progressing as that which occurs in humans or dogs. In 2008 Leif Andersson, PhD, and his colleagues in the Department of Animal Breeding and Genetics at the Swedish University of Agricultural Sciences examined the association between melanoma and gray coat color in horses. Andersson reports that gray horses carry "a unique (genetic) mutation, inherited from generation to generation, that predisposes to melanoma development."

While most melanomas in gray horses are benign, histologic changes during tumor development (e.g., expanding into surrounding muscle) can cause them to become malignant. In humans, for example, a genetic predisposition such as fair skin coupled with exposure to sunlight's ultraviolet (UV) rays can be a melanoma-causing combination.

"Gray horses are protected from damaging effects of UV light by the hair coat and black skin pigmentation," Andersson continues. "The difference in malignancy between gray horse and human melanoma occurs because of underlying mutations that occur in different genes. Our data documents that the specific mutation that causes graying also predisposes a horse to melanoma."

Melanoma development also depends on the type of gray--there is a distinction between a pure gray or white horse and one sporting a "speckled" or "flea-bitten" coat. Horses that inherit two copies of the gray mutation (homozygous)--one from each parent--sport the pure white (pink skin) or gray coat (black skin) color, whereas horses carrying a single copy of the gray mutation (heterozygous) might be speckled gray. "Homozygous gray horses turn gray more quickly and tend to develop more melanoma but do not show speckling," Andersson explains. "Most speckled grays are heterozygous for the mutation and have less melanoma incidence. This molecular understanding of the cause of gray horse melanoma opens up an opportunity to develop an efficient therapy (for treating this condition)."

Melanoma tumors with an actively necrotic (dead tissue) center can rupture and "bleed" black, tarry material--these can become aggressive and disseminate elsewhere in the body (metastasize), including the central nervous system. Veterinarians usually can identify internal melanomas using diagnostic procedures such as abdominal ultrasound or endoscopic exam of guttural pouches (air-filled cavities in the horse's skull, behind the ears).

The best melanoma management advice has been to leave them alone unless they ulcerate, interfere with tack placement, or metastasize internally. But more recently veterinarians have been targeting and eliminating these tumors.

Veterinarians often turn to pharmaceutical and surgical methods. Christina Hewes, DVM, Dipl. ACVS, of the Morrie Waud Equine Center in Delavan, Wisc., for instance, has used the drug cisplatin extensively as a chemotherapeutic approach to equine tumors. "Cisplatin binds to DNA in tumor tissue to cause cross linking (bonds between the proteins that keep cells from dividing), which prevents cell growth and causes apoptosis (programmed cell death)," says Hewes. "It targets rapidly dividing cells, like tumor cells. Local administration causes minimal side effects because skin and subcutaneous (beneath the skin) cells divide more slowly than tumor cells." She notes that cisplatin beads release drug continuously for 30 days, allowing the horse's body to absorb them slowly.

"Melanomas can be removed successfully with debulking (cutting away) only, but if the entire tumor cannot be removed, implanting with cisplatin (beads or sponges) helps to kill residual cells," she says. Residual cells that are left following traditional excision methods can potentially regrow, sometimes with increased intensity and invasion into surrounding tissue. Thus, Hewes prefers surgical removal via laser excision, explaining, "Laser removal vaporizes cells 0.2 mm deeper than the visible incision line. Although this is a small distance, often it is enough to kill residual tumor cells."

A commercial melanoma vaccine (developed for dogs by Merial) is available only through veterinary oncologists, or a veterinarian can prepare an autologous vaccine from a horse's own melanoma tissue (the excised tumor is chopped into bits, frozen, and stored, and then thawed pieces are injected beneath the mane). While vaccine treatment is expensive and not entirely curative, users of either vaccine have reported fairly good success in shrinking melanomas. Researchers also report that the oral anti-ulcer medication cimetidine might slow melanoma growth.

Nongray mature horses that develop melanoma usually have a poor prognosis leading to death due to systemic spread, according to Hewes. In contrast, young horses of any color have an excellent prognosis following tumor removal.

Squamous Cell Carcinoma

Certain horse breeds, such as Paints and Appaloosas, often lack pigmentation at the mucocutaneous junctions, which are where skin meets mucous membranes. These areas--the mouth, within the eye, the vulva, penis, prepuce, and anus--are most susceptible to developing squamous cell carcinoma (SCC). Those located on the vulva, prepuce, and related areas are far more difficult to resolve than those on the horse's cornea.

Elizabeth Carr, DVM, PhD, Dipl. ACVIM, ACVECC, associate professor at Michigan State University's College of Veterinary Medicine, discusses the puzzling locations of SCCs in horses. "The eyes, muzzle, prepuce, and vulva, with only a fine hair covering, receive sunlight exposure to a greater degree than does the hair-covered back of a horse," she says. "Often, these are light-colored areas lacking UV-¬protective melanin pigment. In one study 69% of ophthalmic (pertaining to the eye) SCC developed on nonpigmented, pink skin."

Carr continues, "UV light penetrates skin cells to damage DNA, which results in abnormal cellular growth patterns. Depending on injury type, it may become a precancerous cell or fully transform into a malignant, cancerous cell." The precancerous stage is generally treatable; once cancer cells become malignant, they have the potential to invade surrounding tissue and become more difficult to target.

Typically, cutaneous (skin) SCC only invades locally but might spread to local lymph nodes. "If untreated, lymph nodes develop masses that could invade into deeper tissues, but it's unusual to see skin SCC metastasize to internal organs," Carr remarks. "SCC in the horse has low metastatic potential, with primarily regional invasion (instead)." If the lesion occurs in or near the eye, for example, it might wreak significant damage in ocular tissues. Carr comments that SCC also can originate internally, such as in the stomach.

For cutaneous SCC treatment to be successful, veterinarians must recognize it early. "Surgical excision is a great choice," notes Carr. "However, it's not always possible to completely remove all malignant cells. In those cases I combine therapies by adding intralesional chemotherapy treatment to surgery." For small areas that might contain residual cancer cells, Carr might treat topically with chemotherapeutic 5-fluorouracil (5-FU) or imiquimod (an immune-boosting drug); otherwise, she relies on cisplatin or other chemotherapeutic agents. Not all SCC requires the big guns, though. "Cryotherapy (freezing with liquid nitrogen) is very useful to treat small tumors or tumor margins following excision," she adds.

Fernando Malalana, DVM, GPCert (EqP), MRCVS, of the University of Liverpool Equine Hospital, uses the chemotherapeutic drug mitomycin C (MMC) for equine periocular (around the eye) SCC based on success he's seen reported in human ophthalmology. Malalana recommends four rounds of weekly MMC treatments--topical treatment along with instilling an MMC-solution into the conjunctival sac (conjunctiva is the thin vascular membrane that arises at the edge of the cornea and extends over the white part of the eye and folds back, forming this sac before covering the third eyelid and lining the eyelid) every six hours for seven days--for regression of small tumors. For larger tumors he reports that MMC stops growth or reduces tumor size to enable better surgical resolution. "With the exception of conjunctival lesions, which didn't seem to respond to treatment, 25% (of SCC tumors) reoccurred if MMC was used solely or following surgical excision," he notes.

Elizabeth Giuliano, DVM, MS, Dipl. ACVO, associate professor of ophthalmology at the University of Missouri's College of Veterinary Medicine, recently proposed another approach to treating periocular SCC: photodynamic therapy (PDT). "PDT utilizes a photosensitizing agent and light in the presence of oxygen to produce a localized phototoxic effect," she explains. "This two-stage process first delivers the photosensitizer to the patient, usually by intravenous injection; then, the target tumor is laser irradiated." The therapy kills tumor cells through photochemistry (chemical reactions that proceed with the absorption of light by atoms or molecules), which damages cellular structures, causes tissue inflammation, and reduces blood supply and oxygen availability to tumor cells.

Radiation therapy is yet another effective SCC management tool; however, it is not without its downsides: expense and logistics. The veterinarian inserts "seeds" or beads containing radioactive material into the cancerous tissue, where they damage the DNA of local cancer cells as well as that of normal tissue. "Until radioactive beads are removed, the horse is hazardous and must be housed in a facility licensed for radiation therapy," explains Carr. "In addition, a veterinarian needs special licensing to implant radioactive beads. These concerns make radiation therapy an uncommon, although effective choice."

While most SCC cases are cutaneous and treatable, Carr notes that SCC of the stomach carries a very poor prognosis because it's difficult to resolve surgically. "The biggest issue regarding internal SCC lesions is that they are generally undiagnosed until they've become quite large and invasive," she says. "At this point there is little that can be done."

Prevention and early recognition are key to successful SCC outcomes. For instance, says Carr, "Fly masks on horses with pink-skinned faces or (areas around their) eyes decrease sun exposure. Routine veterinary exam of external genitalia, particularly of pink-skinned (nonpigmented) colored breeds, achieves early recognition, which is a life-saving measure. The biggest factor in success with SCC is the follow-through. If a tumor is removed yet its margins retain residual cancer cells, it needs additional treatment or it'll simply grow back."

Sarcoids

"Cutaneous tumors represent more than 50% of total tumors in horses; sarcoids represent more than 50% of those," reports Youssef Tamzali, DVM, PhD, Dipl. ECEIM, of Ecole Vétérinaire de Toulouse, in France. Certain horses, such as particular families of Arabian horses, might be genetically predisposed to sarcoid tumors. Many believe bovine papillomaviruses (BPV) type 1 and type 2 to be the causative agent of equine sarcoid tumors, although this is not definitive.

Sarcoids tend to be only locally ¬invasive, appearing in several forms: nodular; ¬verrucous (cauliflowerlike); fibroblastic (resembling granulation tissue); or mixed. Veterinarians recommend leaving a flat, "quiet" nongrowing sarcoid alone until it shows activity (e.g., increasing size or irritation), and they suggest always assessing nonhealing traumatic wounds for sarcoids.

Researchers have found that if a surgeon removes sarcoids from a horse without any further treatment, the horse has a high risk of recurrence (more than 50%). Thus, for treating active sarcoids many veterinarians rely on chemotherapy using implantation of cisplatin beads.

A procedure to amplify this therapy, says Tamzali, is electrochemotherapy, or ECT. "This uses electrical field pulses to induce increased cell membrane permeability to antitumor drugs, such as cisplatin," he explains. While Tamzali also uses this method to treat SCC and melanoma, the ECT unit is not yet available in the United States, but can be purchased from Europe. He notes that his research into ECT and other techniques such as electroimmunogenotherapy is ongoing.

Depending on a sarcoid's location (such as near the eyes or ears, on the lower legs, or over or near a joint or bony protrusion), it might be difficult to eliminate completely, but both Hewes and Tamzali stress that preliminary surgical debulking decreases the number of tumor cells to be killed by chemotherapy, reducing the number of treatments needed. "Debulking a tumor also activates remaining tumor cells--rapid growth makes them more sensitive to cisplatin," says Hewes.

Flat sarcoids grow more slowly than other forms, so cisplatin doesn't target their DNA effectively. "Flat sarcoids respond better to topical agents such as 5-fluorouracil," Hewes suggests. The 5-FU, however, will likely cause inflammation, redness, pain, swelling, and associated discomfort.

Topical treatment is another tactic veterinarians use to stimulate a horse's immune response to resolve sarcoids. Imiquimod cream, with its strong antiviral and ¬antitumor properties, has an 80% success rate in reducing all sarcoids' size by at least 75% (Nogueira SA et al., Vet Dermatol. 2006). Other topical paste products include an herbal compound of bloodroot and zinc chloride. Zinc chloride inflames the tumor while bloodroot alkaloids alter tumor cells so they appear antigenic (foreign) to the horse's immune system. This elicits the horse's rejection of small, flat sarcoids.

BCG (bacillus Calmette-Guerin) injections following debulking of nodular sarcoid tumors have been known to shrink tumors located remotely from injection sites; however, these might cause severe reactions. Some veterinarians will administer an autologous sarcoid vaccine when a horse has not responded to other treatments, but this approach has yielded variable results.

Freezing with liquid nitrogen or heating with radiotherapy hyperfrequency are other variably successful approaches to destroy superficial sarcoids.

Researchers continue to examine effective ways to treat sarcoid tumors. For instance, Nasir is investigating a novel treatment for viral sarcoids: gene silencing, or siRNA. "Gene silencing introduces small RNA (the genetic material ribonucleic acid) molecules into cells to 'shut down' specific gene expression and inhibit activity of the target gene so that virus is unable to replicate itself," she says. "We anticipate that siRNA sarcoid treatment will involve topical application and/or injection directly into the tumor."

Take-Home Message

In many cases Hewes suggests that equine tumors of any type should only be treated if they are actively growing, causing a problem, or in an inconvenient location. "A dedicated and vigilant owner is important to monitoring treatment progress and identifying possible regrowth of the tumor," she says. "An owner-veterinarian relationship is instrumental in achieving success for tumor resolution."

Fly Control for Horse Barns

Flies are a fact of life around horse barns and other livestock facilities, or are they? According to a study conducted at the University of Florida, fly populations increase and decrease in relation to some factors that humans can’t control, such as air temperature and other weather patterns. Stable management practices, however, can have an impact on reducing fly populations.

How manure is handled is of major importance. The farm that had the fewest flies removed each day’s manure and stall waste to a separate pile. Within a few days, that pile was mixed into a “working” compost row that was regularly turned, speeding bacterial fermentation and generating enough heat to kill fly larvae. Simply piling manure won’t work very well, but turning and aerating the compost is very effective in disrupting the reproductive cycle of flies. This farm reported no insecticide use, a testament to the efficacy of their management plan.

Two farms in the study chose to spread manure and soiled bedding on fields, an acceptable management practice that can decrease fly populations if it is done correctly. One farm spread the manure thinly over a wide area, allowing the material to break down with exposure to sunlight. At the other farm, waste was spread on the same path day after day, eventually building up a thick layer of wet organic matter that was an ideal breeding ground for flies. This farm had the highest fly population of any in the study.

Insulin Resistance and Iron Overload

Q. - Do you know of any research on how to reduce iron overload in horses that already are insulin resistant and have foundered? Is there an equine equivalent of chelation (a process that binds a mineral to an amino acid) therapy to flush out toxins or heavy metals?

A. - Great question. First, while we did find a correlation between insulin resistance and serum ferritin, the point of our study was to see if the reason iron was accumulating in black rhinos is possibly because they were insulin resistant. This is as opposed to finding out if they were insulin resistant because they were accumulating iron. There is a big difference between the two. Most captive rhinos are overweight (similar to horses) and likely do not receive adequate exercise (again, similar to horses).

My first suggestion, rather than to concentrate on the iron in the diet, is to get rid of the factors that made the horse insulin resistant (such as being overweight and not receiving adequate exercise). By correcting those issues, iron in the diet is likely a non-issue.

That being said, once the problem has developed, feeding a diet lower in iron might be prudent, though there is no good evidence that it can correct insulin resistance (or even that excess dietary iron contributes to insulin resistance). Regardless, if you have concerns, testing your feed/hay to determine iron concentrations can answer the question as to whether it is high in iron.

The National Research Council recommends a minimum of 40 to 50 ppm of iron in the feed (this would be an average of all feed provided). The optimal amount may be, and likely is, higher. This should provide a starting point in determining whether you are providing feed that is high in iron or not.

But to answer your specific question, to my knowledge there are not any recommended chelating agents currently being used. Even if you could remove the excess iron, it would not remove the factors that caused the horse to become insulin resistant in the first place. Those are probably even more important to focus on, though decreasing excessive dietary iron (if found to be doing so) would not hurt.

Possibly Protective Broodmare

Q. I am concerned that if my mare is so protective that she will not let me near her or the foal. How will I deal with that?

A. Some mares are very good mothers and this involves protecting their foals, but it does make it difficult to work with the foal if the mare is excessive in this behavior. You might need to desensitize the mare to your presence.

If her protection of the foal doesn’t mean attacking you I would recommend sitting in the stall or open doorway quietly for prolonged periods of time (30-60 minutes) several times a day. The mare will become comfortable with your being there, and the foal will be curious. Often the foals will approach you if you are quiet.

Always greet the mare first when entering a stall. Food distractions are also helpful.

Cold Weather Leg Wrapping

Q. - In temperatures below 15 degrees I wrap my horses' lower legs in fleece-lined boots at night, as they are prone to laminitis and I hope it will aid circulation as well as keep them warm. They seldom go into the barn, even in very cold temps. Do you think this helps them, or what would you suggest during winter?

A. -  I don't think you will do any harm by wrapping your horses’ legs, but I do think it’s more beneficial due to the support it gives the soft tissues, such as the tendons, rather than aiding circulation. Because horses have a natural perfusion mechanism, they can adjust their temperature using blood vessel dilation and constriction to stay warm.

Also, researchers have proven that cryotherapy (cold therapy) does help ameliorate some of the factors that can cause laminitis, so a horse standing in colder temperatures (e.g., ice water, ground snow) might actually be beneficial.

How much weight can a horse safely carry?

Q: I’m concerned that I may be too heavy for my horse. Staying fit is a constant battle for me, and right now I weigh 175 pounds at 5 feet, 5 inches. My Quarter Horse-cross gelding is 14.1 hands, but sturdy at about 900 pounds. Am I too heavy for him?

A: The basic rule of thumb for a horse’s weight-carrying capacity is 20 percent of the horse’s weight, or, say, 200 pounds for a 1,000-pound horse. (Two hundred pounds would be an approximate upward limit, not an average of what he can carry.) That means a 900-pound horse like your gelding, in general, shouldn’t be expected to carry more than about 180 pounds, including tack, to avoid putting excessive stress on his joints and ligaments.

(Obviously, this rule of thumb assumes that the horse in question is at a healthy weight. A horse that’s grossly overweight at 1,200 pounds, for instance, can’t necessarily carry 240 pounds.)

All that said, there are many variables that affect this rule of thumb. One would be the type and build of the horse, regardless of his overall weight. A tall, relatively lightly built horse that weighs 900 pounds is, in general, going to be less able to carry weight comfortably and safely than a 900-pound horse that’s shorter and more compact—in other words, sturdy, like your gelding. The amount of bone a horse has—meaning the size of his weight-carrying large bones, as indicated by the circumference of the cannon bone—is closely related to the sturdiness factor. The more bone, the better, with respect to a horse’s ability to carry weight and stay sound.

Then, too, your overall fitness (as opposed to just your weight) is also a factor. A strong, fit, well-coordinated but heavier rider can often be easier for a horse to bear than a weak, unfit, awkward but lighter rider.

Your riding ability comes into it, as well. Skill and experience will enable you to be better balanced at all times, which makes you easier to carry at any weight.
So, overall, assuming that (1) you’re reasonably fit for riding and have good basic skills; (2) your horse is indeed a sturdy fellow with reasonable bone; and (3) your tack doesn’t weigh an additional 100 pounds, you should be fine.

Founder vs Laminitis 

Q. - I hear a lot of people use the words laminitis and founder interchangeably. Are these two conditions the same thing?

 A. - That's a more difficult question to answer than you might expect, because the two terms are used interchangeably by a lot of people. However, "founder" implies more of the chronic condition, or the horse that has already had its coffin bone rotate or sink. That is classically a "foundered" horse, versus a laminitic horse that has the onset inflammation of the laminae, which support the coffin bone within the hoof capsule.

Unusual Spots

Q. Our 11-year-old chestnut Morgan mare has suddenly developed white spots all over her body with no apparent cause. She is outside 24/7. The spots range in size from about dime-size all the way up to silver dollar size. There doesn't seem to be any irritation or irregularity in the skin. It looks like someone splattered her with white paint. Are there any clues as to the cause?

A.  It sounds like your horse is exhibiting a form of vitiligo (also called leukoderma or birdcatcher spots), an uncommon acquired pigmentation disorder characterized by progressive areas of pigment loss. These spots typically are only a cosmetic problem and rarely indicate other problems. There is also no known cause or effective treatment. Veterinarians have seen a higher incidence of vitiligo in some breeds (for instance, Arabians) than others, suggesting there might be a genetic basis.
White hair color can also be associated with trauma such as healed wounds or saddle sores from improperly fitting tack, but this does not sound like the case with your horse. Other causes for vitiligo can include skin damage due to sunburn, sun damage, frostbite, and even infections with the parasite Onchocerca. If you are still concerned about these spots I would recommend talking to your veterinarian about them during your next exam.

Differences in Urine

Q. ~  My two horses' urine output is very different. For instance, the ammonia smell of my Thoroughbred's urine is a lot stronger than that of my Quarter Horse. I read that protein affects ammonia levels--could that be why? And the color of my Quarter Horse's urine (in the snow) has always been of a medium to dark orange, while my Thoroughbred's is, well, yellow. What could be causing this?

A. ~  The kidneys produce urine, which contains waste products that need to be eliminated from the body. These waste products include urea and ammonium ion, two breakdown products of protein. The more protein a horse has in his diet, the more urea and ammonium his body will produce and excrete in the urine. Urea is composed of two ammonia molecules and can be broken down to ammonia after being passed in urine. So the answer to your first question is that the more protein your horses consume, the more urea and ammonium they excrete. This contributes to the ammonia smell in their stalls.

However, if your Thoroughbred and Quarter Horse are eating the same diet, that does not explain the difference between the ammonia smell in their stalls. An additional factor that can play a role can be differences is the normal bacterial flora present in the lower urinary tract. Some horses simply have more bacteria with an enzyme called urease that splits urea back into ammonia molecules. If your Thoroughbred has more bacteria with urease in his lower urinary tract, his body will produce more ammonia and, thus, you will notice a stronger ammonia smell in his stall.
Finally, horses also have varying amounts of compounds called urocatechins in their urine. These can be oxidized by light after they are passed and turn orange to red in color, thereby discoloring shavings. In the winter, they also discolor snow and are often confused with bloody urine. The color change only occurs in urine passed by some horses and not others--the reason for this difference is not fully understood.

Why Does My Horse Drool so Much?

 Q. My 18-year-old Arabian gelding likes to drool. My veterinarian has examined my horse and his teeth and says my horse is in excellent health. The drooling is not continuous--it just happens every once in a while, and he'll spit a slobber out. It's pretty gross.
 My questions on horse slobber are:
Could this be an allergy? Is it more behavioral because I give him treats? My vet calls me a "Pez Dispenser"; maybe my horse sees me and starts to salivate? He gets plenty of water, but does he need electrolytes even in winter?

A. Thank you for your question. It sounds like an interesting case, and it is great that you are already working with your veterinarian who has completed a thorough oral examination.

Excessive drooling, or hypersalivation, can have several potential causes. One of the most common causes is slaframine toxicosis from ingesting mold on red clover. Most horses stop the drooling when they are taken off the inciting pasture, although hay might potentially result in exposure as well. That seems unlikely based on the history you have provided.

Other causes include lesions of the oral cavity and tongue, such as dental disease, foreign bodies, grass awns, or abscesses. One horse that I examined about a year ago had a thin wire through her tongue, which was not visible until we took X rays.

Esophageal obstruction and gastric ulceration are potential causes of excess salivation as well. I would not expect an allergy or treats to cause what you have described, but I would certainly defer to your veterinarian who knows your horse and the extent of the situation. If the problem persists or worsens, I would recommend some additional diagnostic tests (such as X rays, ultrasound, endoscopy, and/or CT scan) to rule out a lesion in the mouth or tongue.

(from thehorse.com)

Will Rolling Cause Colic?

Q. My horses normally get turned out daily. After a few days at a show, I took my stall-bound horses to a round pen to roll and move around on their own. Someone suggested I don't do this, because it could cause my horses could get torsion colic.

Does the actual act of normal rolling cause torsion? Also, is there a relationship between torsion colic and time of feeding or amount fed?

A. Normal rolling as a cause of colic is very common misconception among horse owners. However, it is very unlikely for normal, healthy horses to get colon torsion from rolling, so I would allow your horses to do it. Regarding the second part of your question, the only relationship related to feeding and colic is that many concentrates (such as sweet feed) predispose horses to colic but not necessarily to colon torsions. Horses are meant to eat continuously, so frequent feelings are best.