Wolf Teeth

The picture to the right is of the right upper dental arcade. The small little tooth at the very front is a wolf tooth. These small little teeth do not serve any known function, other than to get in the way of the bit. For this reason they are typically removed before a young horse goes into training. Occasionally we will encounter an older horse with bit related issues as a result of a wolf tooth left in place.

They can be highly variable in their eruption pattern. Most are about the size of the one in this picture, but they can also be larger or smaller. Most horses have upper wolf teeth, some only have one, and yet some horses never develop them at all. Very rarely will they appear on the lower jaw. They are almost exclusively only on the upper jaw.

Many people get wolf teeth confused with canine teeth. The wolf tooth is technically the first premolar. They sit just in front of the second premolar, which is a very large tooth, and the first major cheek tooth in the dental arcade. The canines sit quite a bit further forward in the mouth, much closer to the incisors. Canine teeth do not appear in the mouth until 4 or 5 years of age. Another difference from wolf teeth is that they are present on both the upper and lower jaws. A properly placed bit would sit behind the canines, but just in front of the wolf teeth. Most mares do not develop canines, but if they do, they are typically quite a bit smaller than what their male counterparts would have. Canine teeth are considerably large than wolf teeth. They are extremely difficult to extract. Canine teeth are only removed if they are diseased. We do not remove healthy canine teeth.

Because wolf teeth do not serve any known function and because they only serve to be a source of irritation in the bitted mouth, we typically removed them prior to a young horse going into training. The picture to the right is the same horse pictured above, except now the wolf tooth has been removed. To extract the tooth we first numb up the area, cut the gum around the tooth and then gradually work to slide it out with an elevator. The small hole left heals over quickly and uneventfully.

Here is what the tooth looks like out of the mouth. You can see that while they have a very small crown, there is a very long root present.

EHV Outbreak: Update

Here is a link to the latest situation report by USDA of the ongoing outbreak of EHV-1. The exciting thing is that in the past week there have been no new cases on any premise that is not under quarantine. It would appear that this latest outbreak is being brought under control.

USDA's EHV-1 Situation Report (June 8)

Barbaro, Laminitis & 5 yrs.

How can you not remember Barbaro. Can you believe it has been 5 years since he defeated the field in the Kentucky Derby. He brought the world along on his journey through a catostrophic racing injury. However, that is not what ultimately led to his demise. It was laminitis in the other limb that they were not able to get under control which became the last hurdle he could not clear. Check out this video that USA Today put together about Barbaro and the ongoing war on laminitis.

Neuro Herpes Outbreak Update

Here is a link to the USDA's most recent update on the ongoing EHV-1 outbreak. In includes lots of interesting statistics, with breakdowns by state.

http://www.aphis.usda.gov/vs/nahss/equine/ehv/ehv_2011_sitrep_060211.pdf

For more details on the neuro form of EHV-1 see the posting on this blog from May 25.

How Many?

I had a 4-H leader ask me the other day how many teeth do horses have? Sounds like a simple enough question, but the answer is not. It is influenced by several different variables such as age, gender, if any have ever been removed, and if there are any extra ones present. Let me explain.

Let’s start with the basic dentition pattern of the horse. The major teeth of the horse are the incisors, canines, premolars and molars. There should be 6 incisors top and bottom. These are the teeth at the very front of the mouth that are very easy to see. There are 4 canine teeth, two on the top and two on the bottom (one on each side of the mouth). These teeth sit behind the incisors, but in front of the premolars. The bit sits in the space behind the canines, but in front of the pre-molars. The typical adult horse has 12 premolars and 12 molars. They are oriented in a straight row, front to back, top and bottom, on each side of the mouth, with the 3 premolars in front of the 3 molars. With the two top rows, one row on each side, and the two bottom rows all of 6 each, we end up with 24 cheek teeth in all. So in the normal adult male horse we should have 24 cheek teeth (12 molars and 12 premolars), 4 canines, and 12 incisors for a total of 40 teeth. But that is not the whole story.

How many teeth a given horse is influenced by his/her age. The canine teeth do not usually erupt until 4-6 years of age. The last molar does not come in until about 3.5 years of age. The last ‘baby tooth’ is replaced by an adult tooth around 4 years of age.

Gender plays a role in all of this as well, primarily because most mares usually do not develop canine teeth. If they are one of the 28% of mares that have them, they are usually much smaller than those in a stallion or gelding.

Wolf teeth are typically removed at a very young age. They are technically a rudimentary first premolar and can vary tremendously in their eruption pattern. Some horses never get them, some have only one, but most have 2 (one on each side). They are almost always just on the top. It is rare to see wolf teeth on the lower jaw. They do not serve any function for eating or chewing. They often cause bit related problems due to their location and small size. If present, they will sit just in front of the cheek teeth, but well behind the canines. This is the same place that the bit rests in the mouth. We occasionally see them in older adult horses, but most horses have them removed when they are young.

On rare occasion we will encounter a horse with a supernumerary tooth (an extra one). Here is a picture of one I saw just yesterday. It is hard to tell from the picture, but the really long tooth way in the back is actually the seventh tooth back (remember there are only supposed to be 6). Since there is not a seventh tooth on the bottom the upper one just keeps growing and growing. This tooth was an otherwise normal appearing tooth, so we just shortened it with the aid of a motorized burr so that it is no longer rubbing on the opposing gum. This tooth will have to be maintained throughout this horse’s life because it will continue to grow.

So there is the long answer to how many teeth a horse has. The short answer is 36 to 44 in an adult, depending on if canine and wolf teeth are present. If you really want to know exactly how many teeth your horse has, ask your vet next time your horse’s teeth are done and they can give you the exact count for your horse. Of course, that may not be the answer your 4-H judge is looking for.

Outbreak of Neuro form Herpes

I realize I am a little late weighing in on this, but I wanted to make sure you are aware. There is currently an on ongoing outbreak of Equine Herpesvirus Myeloencephalopathy (EHM) affecting horses throughout the United States and Canada. The initial cases were identified at a cutting horse show in Ogden, UT. So far, most of the cases are centered around the western United States. There are, as of yet, no identified cases in Michigan. The challenge with these outbreaks occurring at large shows like this, is that horses from all of the United States can come, be exposed and return home before the first diagnosis is made. This lends to transmission of the virus across wide geographical areas.

Symptoms include fever, decreased coordination, nasal discharge, urine dribbling, loss of tail tone, hind limb weakness, leaning against a wall or fence to maintain balance, lethargy and the inability to rise. First symptoms of a fever and runny nose are usually seen about 2 days after initial exposure. Neurologic deficits do not usually appear until 10-12 days after exposure. The severity of neurologic deficits this virus can cause is what really makes this infection so vicious.

We do not yet fully understand this disease. It is caused by equine herpes virus-1 (EHV-1), more commonly referred to as a rhino virus. This virus is a common cause of upper respiratory infections. However, on seemingly rare occasion, it can mutate and then cause fairly severe neurologic symptoms. There is a point mutation of the virus that has been linked to the neurologic form, but not all horses who become infected with the neurologic form go on to develop neurologic deficits. There is a piece to this puzzle we have not yet found.

This complexity of the virus mutation and variation in symptoms lends to a lot of confusion about what actually constitutes a case of EHM. EHM implies neurologic symptoms, but most agencies define an EHM case based on identification of the mutation in the virus. The problem with this is that a lot of horses that become infected with the mutated form never go on to develop any neurologic symptoms. So a lot of the stats you may be hearing in the press are likely very misleading as to how many horses were ever actually infected with the neurologic form of EHV-1.

Another frustrating point about the neurologic form of EHV-1 is that vaccination is not effective. We do believe that vaccination, with a high antigen vaccine, will lessen the amount of virus circulating and thus lessen the potential for the development of the neurologic form to develop, but we also know that vaccination does not prevent the neurologic form. Vaccination does protect against the respiratory and abortion forms of the disease.

Not all Rhino vaccines are created the same. The high antigen vaccines do a better job a limiting virus shedding. Calvenza is the high antigen EHV vaccine that we use and recommend. There is also a modified live vaccine for EHV, which may be better still at limiting spread. However, there are additional considerations with the use of the modified live vaccine that go beyond the scope of the discussion here. It is best to talk directly with your veterinarian about which vaccine may be best in a given situation. The long and short of it is that over the counter Rhino vaccines are not very good at limiting transmission.
EHV-1 is one of those viruses that can develop into latent infections. Cold sores in humans do this same thing. The virus is always there, but at times of stress (or some other reason) the virus all of the sudden becomes active again. For this reason, seemingly healthy horses potentially could be latently infected and then when placed in a stressful environment, like a horse show, start shedding virus again.

This, is really intended to only be a brief summary about some of the complexities of this virus and the challenges we face in dealing with such outbreaks. The neurologic form of EHV-1 is not anything to mess with. It is a truly nasty disease. Our best strategy for control at this point is good biosecurity practices (see the links below). Vaccination may be of some benefit in limiting the spread of virus, but does not currently protect against the neurologic form. As you can image, there is a ton of more information about this. Here are a couple of good resources if you want to learn more.

USDA info and updates
FAQ’s, provided by AAEP
USDA Equine Biosecurity brochure
AAEP Biosecurity Guidelines
AAEP EHV Control Guidelines

COW: Keep an Eye Out For...

Wow, I did not realize it has been well over a month since my last posting. I will try to make up for it over the next week or so.

Here is an eye that was presented to me recently. What do you think?

This is a tumor, more specifically a squamous cell carcinoma (SCC), involving the nicitans, or more commonly refered to as the third eyelid. The nicitans is a structure that, when the eye is open, hides is the front corner of the eye. In fact, most people do not even realize it is there. It acts as a third eyelid and can slide over the eye. It is mostly made up of conjunctiva with a cartilidge frame that gives it its shape and structure. Below is a picture of the retracted third eyelid. Sorry that it is a little out of focus, but I think you can get the idea.

SCC's are not uncommon tumors of the eye. They have a strong propensity to develop in nonpigmented skin. Horses with white skin around the eye are at higher risk. They rarely spread to other parts of the body, but they can become locally invasive and will rapidly expand into adjoining tissues. This can become a significant problem especially when the eye becomes involved.

Fortunately, this SCC only involved the third eyelid, so we were able to surgically remove it before it invaded the eye itself. Here is what it looked like immediately following surgical removal.

This was a big horse. This last picture pretty much explains why we have such substantial stocks at the clinic.