I realize this article is a bit one-sided. I am catering more to the needs of my gray horse owners in this article; however, if you don’t own a gray horse I would read on for two very important reasons. 1. You may someday own or look to buy a gray horse and this information would be helpful and 2. It is not completely isolated to gray horses, although they are the most commonly afflicted. That said, let’s discuss our main topic, melanomas.
A melanoma is a type of skin tumor and one of the most common forms of skin tumors found in horses. Most every owner of a gray horse knows what they are and has seen them if they have just done a quick look under their horse’s tail. No one knows quite for sure why gray horses are more susceptible to this affliction. We do know that unlike humans (who develop melanomas from over exposure to the sun) the fact that their skin is black in color which should help shield ultraviolet radiation as well as the fact that most of these tumors occur in areas shielded from the sun (e.g. under the tail head) it does not appear true for horses. Whatever the case, it is estimated that over 80% of gray horses over the age of 15 years will develop at least one melanoma during their lifetime.
The breed of horse isn’t specific, although Arabians, Percherons, and Andalusians seem to be over represented (likely due to the fact that a majority of them happen to be gray). So, all you gray horse owners, let’s do a run through. Pick a time when you can do a thorough evaluation of your horse’s skin and bring a small notebook with you to jot spots down for future reference. Melanomas can be hard or soft (most of the ones I see are firm) and they can be single or appear in clusters. At first, most melanomas are subcutaneous (which means they are right under the skin) but covered by normal hair-covered skin. But over time as melanomas grow they become more obvious. As they grow they are often times not covered by normal hair-covered skin but appear to be dark brown, gray, or black in color. As they continue to grow some even can be ulcerated on top and exude (drain) a dark black substance. The ones that tend to become ulcerated are often under the tail head and become irritated from constant tail wishing especially in the summer when the flies are bad. The most common places to find melanomas on horses include under the tail head or surrounding the rectum (and vulva in mares) and within the opening to the sheath (in males). They can also be located on the ear margins, on the head, on the neck and around the salivary gland (under the tongue). So carefully (some horses don’t like some of those areas “checked out”) check out your horse, intensifying your search on the most common areas and mark down what you find.
The word melanoma can strike fear into most humans and rightly so. In humans, melanomas have a nasty habit of metastasizing (or spreading) to other parts of the body, especially internally. However, horses with melanomas have a distinct advantage over us since the large majority of melanomas in horses develop slowly over a number of years without metastasis and can remain benign (noncancerous) for 10-20 years. In this case, the melanomas tend to be more unpleasing to the eye more than problematic for the horse. If a benign tumor gets large enough it can “functionally” be a problem e.g. a large tumor not allowing the sheath to drop when urinating, or one pressing next to the rectum causing problems with defecation or even with breeding if down next to the vulva.
Not going into all of the different gradations of melanoma classifications, equine melanomas can generally be broken down into three categories. 1. Slow development over several years, benign, without metastasis the category we alluded to in the preceding paragraph. 2. Benign tumors that have been present for years and then suddenly turn malignant and begin to metastasize. 3. Tumors that are malignant from the first appearance and metastasize quickly. Category 3 also contains a very rare incidence of foals actually being born with malignant tumors. Although we are lucky that most of the horses fall into the first category, we unfortunately never know when they may enter the second category. Malignant (aggressive cancerous) melanoma characteristics can include rapidly spreading series of lumps or nodules that can sometimes resemble vast, rippling sheets of masses across the tissue. Obvious or dramatic changes in tumors that have been the same for quite a while may also be a sign that a tumor may be turning malignant.
Since the majority of the horses have Category 1, the general treatment for melanomas is usually what I like to call “aggressive benign neglect” i.e. keep an eye on it and call me if there is any quick change in the size or the appearance of the mass. Most gray horses continue to live very happily with benign melanomas that cause little to no discomfort. For those horses in Category 1 with large tumors that are causing “functional problems” there are some treatment options as well. For those that are in surgically accessible locations, we can surgically remove them but recurrence is common. Other treatment options include cryosurgery (freezing) the area and chemotherapy (usually injecting the lesions themselves) with chemotherapy agents such as cisplatnin. The major problem with most of these therapies is that recurrence is common within a few months to a year.
As for the other Categories that include malignant tumors, generally by their very nature it is more difficult to treat with conventional therapies. The large sheets of tumors or large bundles make it difficult for removal, freezing or injections since they are often times too numerous for those types of therapy. However, there are some “systemic” (whole body) therapies available now as well. One of these is treatment with cimetidine (trade name Tagamet®). Although success can vary upon several factors, the drug is often able to reduce the size and number of a horse’s tumors. A good response to cimetidine is a 50% reduction in the size and / or number of the tumors with no progression of the disease for several years, and it is estimated that 30-50% of horses treated do respond to some degree. Now for all of you out there with horse with Category 1 tumors, the therapy will not likely work as well. Why? Because this therapy works much better on “active” melanomas by boosting the body’s natural defense system against the actively dividing cells. In the case of Category 1 tumors; however, the cells usually aren’t “actively” dividing since it is such a slow progress so the therapy doesn’t work as well.
The other systemic therapy is a vaccine. Not the normal type of vaccine that we vaccinate horses for annually, but an actual “custom made” vaccine created from one of your own horse’s melanomas. A tumor is removed from your horse surgically; the melanoma is then packed on ice and overnighted to an oncology laboratory where they will produce a vaccine designed to boost your horse’s immune system to recognize and attack the tumor cells. According to the laboratory, most clients report some success and some have reported complete regression of the disease.
Although the systemic treatments are promising, they aren’t cheap or for that matter convenient to administer. Cimetidine is best given by mouth three times a day, and yes we actually mean eight hours apart, three times a daynot just whenever you get time to run out and give it. Most treatment protocols consist of continuing until you see no further improvement for 2-3 weeks, usually at a minimum of 3 months of therapy and sometimes for several more months after. Therefore, at the current recommended dose you will likely spend approximately $35.00 a month on medication along with the dedication of treating your horse every eight hours. Likewise, the vaccine as you can imagine is not the most economical route as well. I have an email to the doctor that was listed as an expert on the subject for updates on statistical data as well as pricing, but from previous information I could find on the subject, the cost was over $500.00 for the vaccine, which would not include surgical removal of the tumor, overnight shipping of the tumor to the laboratory and administration of the vaccine every 2-4 weeks in conjunction with an intravenous immunostimulant product. For those who are possibly interested in this melanoma vaccine, I can give you further information as I receive it and we could get a better idea on a cost estimate.
So in the end, there is no single magic cure for melanomas. As long as your horse stays in Category 1 we will likely continue to monitor the areas for growth and change and treat with “benign neglect”. If you feel that your “old gray horse ain’t what he used to be” and that he may be at risk of Category 2, please call the office for an evaluation. As more research is gathered on the topic of equine melanomas, hopefully further medical therapies will be available that may actually completely cure the disease. For further information, please contact us.
Out of convenience and care for our clients and patients, our mobile clinic maintains a mobile phone system so you can easier reach us. When we get very busy during the day, be rest assured we check the messages quickly after receiving them; however, if it is a simple question or an appointment we often times finish working on our current patient / farm and call you back during the drive to the next appointment. Likewise, if we are in a poor phone reception area (such as Wheatfield, Morocco, Lake Village, etc…) we may not be able to retrieve your message or call you back for a while. We have had an increased number of non-emergency phone calls after hours and on the weekends. Please understand that with our cell phone system, even if you call just to leave a message, the phone is still disruptive and then the message needs to be checked to verify if it is an emergency or not. Please hold all appointments and non-emergency question phone calls until normal business hours (8:30 am 4:30 pm Monday through Friday). My family and I thank you.
I decided to add an article on virus detection and treatment since we have seen several cases lately. Often times when an owner notices a virus in their horse they believe that it is likely a colic they are facing, since the first thing usually seen is that their horse does not want to eat and is acting depressed. Although those two clinical symptoms are seen commonly with cases of colic (abdominal pain) they can also be seen when a horse has a fever. Do you remember the last time you had a fever and how yucky you felt? Well, horses can feel like that too and often times just kind of stand there, quiet and depressed and tend not to move around a lot or eat their feed.
So you notice these clinical signs in a horse and you do one of two things…1. You call your veterinarian who asks a few questions and then the kicker one…Have you taken your horse’s temperature? Followed by the ever so loved… What is your horse’s temperature? And then I get the collective sigh. Yes, I realize that taking a horse’s rectal temperature isn’t the most glamorous job in the world, but it needs to be done. So let’s do a quick run through on how exactly to do it. First things first, get a thermometer. It doesn’t have to be a special horse thermometer, just run down to the local pharmacy and pick up a digital thermometer or confiscate your family thermometer for the time being and delegate it to the barn afterwards (for the sake of your family don’t bring it back into the house for use no matter how much you clean it off). You can also apply a small amount of KY Jelly® or Vaseline® on the tip of the thermometer to ease in the insertion of the thermometer. Have someone hold the horse’s head, stand to the side of the horse near the flank, grab the horse’s tail and bring it to the opposite side of the horse you are standing, lean over and get a look on your “target” and lean back and insert the thermometer into the rectum up to the area where you read it. If you miss the first time, lean over again and take a look and try to redirect your aim. If the horse is kicking or you are concerned about getting hurt, then scrap the idea and you can get a professional to do it. A horse’s temperature should normally be anywhere between 99.0º 100.8º F. And no, I won’t buy “my horse doesn’t feel warm” or that you’ve checked his “forehead”. It just doesn’t work that way in horses. So now armed with more pertinent information you can call your veterinarian.
And yes I did mention there were two things most people do… 2. You administer flunixin meglumine (aka Banamine®) to your horse for the supposed colic. Is that going to be a major problem in a virus you ask? No…actually for a horse with fever, flunixin meglumine is a good medicine (analgesic pain killer, antipyretic fever reducer and anti-inflammatory) to reduce fever and make a horse feel better, but if you administer it before you get an accurate temperature you may cover up some important clinical signs that would allow a veterinarian from treating your horse properly. So again, take your horse’s temperature or have someone else do it that knows how.
If your horse in fact has a fever, then to rule out either bacterial infection or viral infection, blood work is often ran. A low white blood cell count is often indicative of a virus and an elevated white cell count is often indicative of a bacterial infectionalthough discrepancies may arise. It is true in veterinary medicine as it is in human medicine, there is not much you can do for a virus except supportive care. Keep the fever reduced, treat secondary problems as they arise, encourage fluid intake or sometimes IV fluids are necessary, etc… As I alluded to earlier, I’ve seen several cases of a nonspecific virus lately with fever, anorexia (not eating), depression and low white cell counts. All have recovered uneventfully, but recovery has taken anywhere between 2 days to 10 days. By recovery I mean the fever has broke and the appetite is back, but often times a good rule of thumb for performance working horses is to give them a week off for every day they have a fever.
Just as with us, this is the time of year our horses may be more prone to sickness. By keeping a close eye on your horses, seeking treatment early in the disease and properly supporting them during their recovery…hopefully your down time from using your horse will be at a minimum.
Winter is upon us again, so just a quick reminder on some winter woes your horses may be facing.
Water consumption can be a problem for horses in the winter months for a couple reasons. 1. Their water source may be frozen. 2. They may not be as ready to drink freezing cold water when they themselves are freezing cold. When the temperatures drop below freezing, outdoor water sources can freeze easily. Even if you break off the large chunk of ice when you do chores in the morning, that water source will quickly freeze back over as you leave down the lane for work. It is important to get a safe water heater unit for your water trough during the winter months to prevent your water from freezing. I say safe, because it is also important not to accidentally electrify your horse’s only water source with a faulty heater. This is not an area to cut corners. Horses also decrease their amount of drinking during the winter for the same reason you wouldn’t be desiring an ice cold pop after you’ve been standing outside all day. If you have access, it is oftentimes a good practice to offer your horse warmed water during meal times to encourage more fluid intake.
Decreased fluid intake and a change in diet (going from summer grasses to only dried hay) leads to a second common winter problem, impactions. Decreased fluid intake can lead to dehydration which can result in your horse being “constipated” or impacted. Impacted horses sometimes act mildly colickynot wanting to necessarily eat but also not being overly uncomfortable (i.e. rolling, kicking at their sides, etc…) as you would expect gas or surgical colics to be acting. Treatment consists of fluids, fluids and fluids…both orally and intravenously. Follow the previous paragraphs guidelines on encouraging your horse to drink more.
Ventilation is often another problem for horses in the winter. It usually is more of a problem in large, heated performance barns although I have seen it in smaller barns as well. The problem often revolves around people wanting to keep the barn as air tight as possible to prevent the horses from getting cold (and heaven forbid growing some winter hairI know, I know, all of you performance riders don’t get up in armshear me out) and they, in a round about way, accidentally increase the number of allergens and harmful odors that can cause respiratory problems in a horse. If you’ve ever walked into a heated establishment in the middle of winter and the smell of ammonia stops you dead in your tracks and you wrinkle your nose, you know what I’m talking about. This type of problem can greatly increase your horse’s chance of getting sick in the winter. Yes, it’s important to provide adequate wind breaks and protection from the cold; just don’t go overboard.
Those are some common winter problems that I see each year, if you have any further questions or would like some more suggestions on how to help prevent your horse having winter woes, please contact us.
Did You Know?
Did you know that a mare can control the size of her fetus? In other words, it is extremely rare for a horse to have a foal that is too big to pass through her pelvic canal. That is not true of cows; that is why you always see bulls being advertised as “small” and why you always hear about having to pull calves. If a mare has a dystocia (a problem with delivery) it is usually centered around the presentation of the foal, i.e. the leg is bent back, the knee is bent, etc... Now, unfortunately for all my miniature horse owners, this nice rule of thumb kind of flies right out the window since they are a bit small the way it is.
In an effort to preserve my sanity and my family unit, I will be taking a family vacation over the Christmas Holiday. Our clinic will be closed to appointments and emergencies Monday, December 22nd through Monday, December 29th. My technician, Mandy, will be available to field calls and schedule appointments during normal business hours and will try to help you decide if your horse should be further evaluated by another veterinarian. I hope you and your family (including all that sleep in stalls) have a wonderful holiday season.
Horse New Year’s Resolutions
As 2004 draws closer and we are thinking of New Year’s Resolutions for ourselves, maybe we should help our horses with their own resolutions. Thanks to Lynn for sending us these hilarious horsey New Year’s resolutions. What I loved most about them is that I can think of one of my patients that should strive to reach at least one of these resolutions so I was sure that most of you would find them appropriate as well with your horses. Enjoy!
Oh and don’t forget to wish all your horses a hearty “Happy Birthday” on January 1st, the universal birthday for all horses.