Misunderstood, Misused, & Misdiagnosed Disease #2: Lyme Disease

I hope you enjoyed reading about Misunderstood, Misused, & Misdiagnosed Disease #1: EPM.  In that post I explained how some horse enthusiasts (trainers, owners, etc) have used this disease to explain any number of abnormalities that their horse is exhibiting.  EPM is quite a convenient disease to blame for oddities because it affects horses in so many different ways.

Another disease that I have found that is easy to over-use as a diagnosis is Lyme Disease.  In this post I would like to briefly explain what Lyme disease is, why it is easy to misuse as a diagnosis, and how a veterinarian evaluates a horse to determine if the Lyme Disease is responsible for the clinical abnormalities that the horse exhibits.  I will not get into the complex pathology and treatment options of Lyme Disease in this post.

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Lyme Disease is one of several nasty diseases that can affect multiple species, including humans, dogs, and horses.  It is caused by spirochete bacteria named Borrelia burgdorferi (Bb).  These spiral-shaped bacteria are transmitted to humans and animals by species of Ixodes ticks.  The deer tick or blacklegged tick (Ixodes scapularis) transmits Lyme Disease to humans and animals on the east coast and north central United States, while the western blacklegged tick (Ixodes pacificus) is responsible for cases on the west coast of the US.

The Blacklegged Tick can carry Bb bacteria and typically infects animals and humans on the east coast and upper midwest of the US.  Source:  cdc.gov/lyme/

The Western Blacklegged Tick (Ixodes pacificus) can transmit Lyme Disease to animals and humans in the western US.  Source: cdc.gov/ticks/

 

 

 

 

 

 

A tick becomes a host for Bb when it sucks blood from an infected animal or human.  That tick can infect others when it attaches to another being and begins to feed on them.  Ticks salivate excessively during feeding, and the bacteria are present in the saliva.  Usually the tick needs to feed for over 24 hours before the Bb bacteria are transmitted to the host.  The longer the tick feeds, the greater the chance that Bb bacteria will be transmitted to the host.

Once transmitted, the Bb bacteria will be attacked by the body’s immune system.  This attack is what causes the symptoms that are present when an animal has Lyme Disease.  Symptoms/clinical signs are different for humans versus dogs versus horses.  For the purpose of this post, we will only focus on horses.

Now I’d like to focus on what makes Lyme Disease a Misused, Misunderstood, and Misdiagnosed disease.

#1 – Large Variety of Clinical Signs

Below is a graphic listing some of the clinical signs that have been seen in horses with Lyme Disease.

Important factors to consider:

• Not every horse infected with Lyme Disease will develop all of these signs.
• Several of these symptoms are difficult to recognize (low-grade fever, skin sensitivity).

“For some reason humans like to have one explanation for everything, so our minds will want to look for one disease that causes all of these problems.  Lyme Disease is such an easy way to explain all of these issues and it is treatable!  However, things are not usually that simple.”

#2 – Many other (and sometimes more common) diseases show similar clinical signs

Lets look at a few examples.

Case 1:  A performance horse has had chronic weight loss, poor performance, and some behavior changes (lethargy)  over the past 6 months.  Based on the clinical signs listed above it seems like the horse is a shoe-in for Lyme Disease diagnosis.  However, as we gain some more history on the horse we find that it is a nervous horse and many times will not eat his grain.  Based on this information, the vet decides to perform endoscopy and look at the stomach for evidence of ulcers.  In this case it is highly more likely that gastric ulcers are causing the horse to not eat, lose weight, and become more lethargic.

Case 2:  An older horse is a pasture ornament for 90% of the time, but sometimes the owner really feels like taking him camping and riding for 3-4 days over rugged terrain.  The horse always is sore and lame after the first day, but it is a different leg each time.  He seems fine after getting home and spending some time resting though.  Again – Lyme Disease fits right in with a reasonable diagnosis.  But after using some common sense, we can assume that the owner needs to keep her horse in shape and not expect him to be a weekend warrior.

Muscle soreness is a common clinical sign for horses with Lyme Disease, as reported by veterinarians. However, there are many other more common causes for muscle soreness that should be ruled out first before jumping to Lyme Disease. Source: equisearch.com

There are myriads of issues that can have the same symptoms as Lyme Disease, and sometimes more than one problem can be happening at once.  For example, a mare might be in heat (which causes behavior changes and hypersensitivity) and have a injured tendon (causing lameness and swelling).  For some reason humans like to have one explanation for everything, so our minds will want to look for one disease that causes all of these problems.  Lyme Disease is such an easy way to explain all of these issues and it is treatable!  However, things are not usually that simple.

# 3:  Lyme Disease is not easy to definitively diagnose

Like EPM, a diagnosis of Lyme Disease is not simply a test with a positive or negative result.  To reach a diagnosis of Lyme Disease, the vet has to use deductive reasoning and their experience.  For an example I would like to point to a graphic used by veterinarians when trying to make a diagnosis of Lyme Disease in a dog.

When a dog presents to a vet with lameness and fever, they must use powers of deductive reasoning to determine the diagnosis of Lyme Disease because there are many other disorders that cause lameness and fever.  The same goes when examining horses.  Source:  ACVIM Consensus Statement, Journal of Veterinary Internal Medicine 2006.

When a vet is presented with a horse that is a Lyme Disease suspect (is showing appropriate clinical signs) they must ask themselves several questions:

1.  Does the horse live or has it been to an area where ticks that carry Bb are present or endemic?
2. Have ticks been found on the horse?
3. Have other disorders that cause similar signs be ruled out?

If the answer(s) is(are) yes to those questions, then the next step is to draw a blood sample and send it in for testing.  Usually the test is looking for the presence of antibodies to Bb present in the horse’s blood.  The presence of the antibodies indicate that the horse has been EXPOSED to the Bb bacteria.  It does not tell us if the horse currently is infected and fighting Lyme Disease.  For that answer we have to look at the number and type of antibodies present in the blood.

Large numbers of antibodies in the blood typically indicate an active infection, but these numbers are all relative.  There are no exact cutoff numbers that say “if your horse has X amount of antibodies then they should be treated for Lyme disease”.  The decision on whether to treat or not is best left up to your veterinarian, who has clinical training and experience in determining what horses might benefit from treatment.  For more information on testing and interpreting results, I refer you to this nice summary from Cornell University.

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To summarize:  Diseases that have many vague and intermittent symptoms are easy to jump to as a diagnosis for any ailment your horse may face.  This is especially true when there is no diagnostic test that is clear cut, and when treatment may or may not improve the clinical signs of the disease.  Too often these type of maladies are misused by horse enthusiasts to explain all of the problems that they see in their horse, mostly because the disease is misunderstood.  It would be best for the horse if we can keep an open mind and scientifically search for a correct diagnosis, instead of conveniently jumping to diseases like EPM and Lyme Disease.

 

 

 

Horse with fever and diarrhea – could it be PHF?

It is late summer/early fall here in the United States.  The weather can quite variable – one minute its hot and sunny, and the next day it cold and blustery.  During this time of the year veterinarians in certain portions of the country will also start seeing an uptick in cases of horses with fever and/or diarrhea.  I think this would be an excellent time to discuss how your veterinarian might approach the diagnosis and treatment of your horse if it develops these symptoms.  I also think it is pertinent to explain why your vet might lean towards one diagnosis over another, depending on the season.  So, lets go through a typical case that I see during this time of year….

Later summer to early autumn is the classic time to see cases of Potomac Horse Fever in the United States. Source: absorbine.com

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(phone rings)

Horse Owner:  Hey Doc, I noticed that my mare did not finish her grain this morning and now she won’t even look at her food tonight.  She also is acting dumpy.

Me:  I’m sorry to hear that.  Have you seen her pass any feces?

Horse Owner:  Not yet.  She’s not really acting colicky though.  She just stands in her stall with her head in the corner.  Now that I’m watching her, I can see it looks like she is breathing fast and her nostrils are flaring.

Me:  Oh, well that sounds like a fever.  Can you take her temperature?

Horse Owner:  I don’t have a thermometer and I really don’t feel comfortable doing that.  Can you just come see her?

Me:  OK.  Just keep her in the stall, pull her food away, and keep water available.

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(Later, at the barn)

Horse Owner:  I’m really worried about her Doc.  What do you think is going on?

Me:  Well she definitely is fighting something.  Her temperature is 105.0°, which is pretty high.  Anything over 101.5° is what I would consider a fever.  Her lung and heart sounds are normal, but their rate is increased.  Her gut sounds are very active, which means that colic is less likely.  I’m a bit concerned about her gum color though – its kind of pale with a dark purplish line just above the teeth.  It’s what we call a “toxic gum line”.

A “toxic” gum line in a horse refers to the darker pink to purple color above the teeth in contrast to the light pink above that.
Source: ckequinehosiptal.com

Horse Owner:  Toxic gum line?!!  Do you think she ate some poison???!!

Me:  No, no, nothing like that.  The term “toxic” refers to endotoxins, which are toxins that normally are present in certain bacteria.  When the membrane that surrounds the bacteria is disrupted, then these toxins are released into the circulatory system.  The toxins can cause a lot of the clinical signs that your horse is exhibiting – fever, gum color abnormalities, and an elevated heart rate.

Horse Owner:  Do you think she has a bacterial infection?

Me:  I am not sure at this point.  Endotoxemia can be caused by bacteria that normally live inside the horse’s GI tract and release small amounts of endotoxins as they die naturally.  In a normal situation the GI tract has a nice barrier that prevents the endotoxins from getting into the bloodstream.  However,  if the GI tract gets inflamed or loses blood supply, then the endotoxins can get into the bloodstream.  They basically cause a massive inflammatory reaction because the body is trying to get rid of them.  So we can see these symptoms if anything causes the intestinal lining to become inflamed or lose blood supply.

Horse Owner:  So how do we treat this problem?

Me:  First we start by administering anti-inflammatory medication.  This will help decrease her fever and make her feel better.  It also is to prevent laminitis/founder – which is also a side effect of endotoxemia.  Second, I would like to take a blood sample and run a complete blood count and serum biochemistry panel.  This will give me an idea of the severity of the inflammation as well as tell me how her vital organs are functioning.

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(The next day I call the owner.)

Me:  How is your horse doing today?

Horse Owner:  She still is pretty dumpy today and now I think she has diarrhea.  Its in her tail and on the stall walls.  Her temperature is normal though!

Me:  I had a feeling this would happen.  The results from the blood work came back showing very low white blood cell counts, which most likely means that her body is fighting an infection and the blood cells have moved out of circulation and to the area of infection.  Her protein and red blood cell counts are up, which means that she probably is also a bit dehydrated.  The good news is her kidneys and liver are functioning.

Horse Owner:  OK.  What kind of infection?

Me:  Based on the time of year (late summer/fall) and her clinical signs (fever followed by diarrhea), we most likely are dealing with Potomac Horse Fever.  According to our records it looks like we didn’t vaccinate for that this year.

Horse Owner:  Yeah, I know.  I was tight on money at that time so I skipped that vaccine.  Plus, I thought you said that the vaccine wasn’t going to protect her from it.

Me:  It’s true that the vaccine is not 100% effective, but horses that are vaccinated and then infected tend to have a less severe form of this disease, at least according to many equine vets out there (myself included).  So we do recommend that vaccine so that if a horse is infected they have a better chance of coming through the disease more quickly and with less side effects.

Horse Owner:  How did she get Potomac Horse Fever (PHF)?  None of my other horses are sick and she hasn’t traveled anywhere.

Me:  Potomac Horse Fever is a disease that is transmitted by the horse ingesting insects or bat feces that are infected with a bacteria called Neorikettsia risticii.  The life cycle is kind of complicated, but basically the bacteria live inside of a parasite (cercariae) that infects fresh-water snails.  When the weather is warm the parasite leaves the snail and gets eaten by the larvae of aquatic insects (May Fly, Caddis Fly, Dragonfly).  Inside the insect larvae, the parasite enters a different part of it’s life cycle and becomes a metacercariae, which is still housing the bacteria (N. risticii) inside of itself.

Potomac Horse Fever Life Cycle
Source: threeoaksequine.com

If a horse accidentally ingests a metacercariae, the parasite will pass through the stomach untouched because it is acid resistant.  The parasite carries the bacteria all the way to the intestines of the horse.  The bacteria then infect the cells that line the intestines and cause massive damage to the intestines.  This is what causes the horse to have diarrhea.  Also, a large portion of the white blood cells leave the blood circulation and to attack the bacteria – which is why their counts are low.

Horse Owner:  So the horses get the bacteria from insects in the environment, not other horses?

Me:  Technically, a horse could get the bacteria from another horse if he ate large amounts of the infected horse’s feces, but that is highly unlikely.

Horse Owner:  What about humans or other animals?

Aquatic insects as seen above can carry the parasite that carries the bacteria that causes PHF.
Source: anokaequineblog.wordpress.com

Me:  Humans do not seem to get this disease.  There is some thought that bats may carry the disease, but it hasn’t been seen in other animals.

Horse Owner:  I thought horses had to be near water to get Potomac Horse Fever.  Is that not true?

Me:  Unfortunately that is not true.  Any place where there is enough fresh water for insect larvae to live will do.  This includes areas under stall mats, water tanks, etc.

Horse Owner:  So now what should we do?

Me:  Luckily there is an antibiotic that is highly effective for treating PHF – oxytetracycline.  Additionally I recommend some IV fluids to help with hydration, especially since she was already dehydrated last night.  We will keep her on the anti-inflammatory medication to control her fever and prevent laminitis.  Also, it would be a good idea to ice her feet to prevent laminitis.  Most horses make it through the fever and diarrhea just fine (with appropriate treatment).  The part that can be deadly is usually the laminitis.

Horse Owner:  Well I guess I can load her up and take her to stay with you guys at the hospital until she can come home.  Is there anything I can do to prevent my other horses from getting PHF?

Me:  Number one – vaccinate your horses before the warm weather gets here.  The best time is springtime, however in some areas of our country they recommend a booster in the fall.  Number two – practice insect control measures.  Limit places where standing water accumulates and keep the environment as clean and dry as possible.  You should also turn off lights at night to discourage bugs from hanging around the barn and/or sheds.

(End conversation)

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I hope you all found this change of pace in my blog refreshing!  Again, please let me know if there are any topics of interest that you would like me to discuss.  Thank you!!

Getting your mare in foal – the choices, costs, and considerations

So you have decided that you want a foal out of your favorite mare…..

She is your best show horse, never lame or sick, and can handle any type of rider on her back.  You know she won’t be around forever, and she has the conformation, genes, and temperament that you want in all of your horses.  Once you start thinking of her future foal(s), you start to get really excited.  And getting her in foal should be pretty easy, right?  Just throw the mare and stallion in a pasture together and they will get the job done.  Then 11 months later you will have a beautiful healthy foal running around your pasture with its mother while you sit on your porch and enjoy a lovely cup of coffee.

Dreaming of your mare and foal playing in your pasture….
Source: kimballstock.com

Sorry to interrupt the daydream, but here comes the voice of reason :(.

Things are usually not quite that simple.  Yes, the above scenario sometimes does happen.  However, depending on multiple factors (breed of horse, age of mare, etc.), getting a mare in foal can be a challenge.  I’d like to discuss some of the considerations, choices, and costs that the mare owner should be aware of before deciding to breed their horse.

Considerations

– Age of the mare:  If your mare has never foaled before, she is termed a “maiden mare”.  Older (over 13 years) maiden mares are notoriously difficult to get in foal for the first time.  If your mare has had foals in the past but is now older (over 20 years) she may also have some troubles getting pregnant.

– Breed of horse:  Depending on the type of stallion you would like to breed her with, you may not be able to have your mare bred by the stud in a pasture (“pasture bred”).  Sometimes the nearest quality stallion is located hundreds of miles away, in which case you would have to trailer your mare out to that farm and leave her there until they told you she was bred.  Then you get to trailer her back and have your vet confirm the pregnancy.  Don’t get me wrong – this procedure is quite common in the Thoroughbred world – but most other breeds ship semen to you for artificial insemination.  Artificial insemination is unfortunately not as simple as just injecting the semen into the mare and walking away – more on that later.

Choices

– The “stud”:  One of the most exciting parts about getting a mare bred is getting to pick out her stallion.  There are websites and magazines galore with beautiful pictures of stallions and lists of their accomplishments.  And when you are dreaming of that foal it is fun to picture what each stallion could contribute to compliment your mare’s traits.  Some practical things to think about once you have narrowed down your search include:

1)  The contract.  CAREFULLY read and re-read the breeding contract and make sure you understand it.  If not, ask your veterinarian or trainer or other horse professional to go over it with you.  Some contracts have “live foal guarantees”, others do not.  It is important to understand exactly what you are paying for and why.

It is important to understand everything outlined in a breeding contract when selecting a stallion for your mare.
Source: Equinelegalsolutions.com

2) The breeding stats.  It is a good idea to know how many live foals this stallion has produced per year, how many mares he is bred to each year (his “booking”), and the average number of times a mare is bred to him before she gets pregnant.  Additionally, if you are having his semen shipped for artificial insemination, you want to know how well the semen ships, and average number of shipments before a mare gets in foal.  If a stallion owner says “This stallion got 10 mares in foal last year” – that is a very vague statement.  You don’t know how many mares he attempted to breed, how many live foals were born, and what type of breeding took place.  He could have bred over 100 mares, gotten 10 in foal, had 2 live foals, and bred 20 mares in pasture and 80 mares via artificial insemination.  Ask the stallion owner the hard questions.  If they refuse to answer them, then something fishy is going on and it is best to choose another stud.

3)  The reputation of the stallion, breeding farm, and owner.  This runs along the same line as the stats.  If things seem kinda shady, they probably really are.  A stallion owner who is trying to sell semen should want to work with potential buyers and answer their questions honestly and promptly.  If you request to visit their farm, they should be more than happy to take you on a tour!  You are the customer and the way they make money.  Obviously, don’t be obnoxious and call at weird hours :).  A good piece of advice is to speak with other mare owners and get recommendations on studs and breeding farms.

– Type of breeding.  Almost every breed association accepts foals born from artificial insemination (The Jockey Club / Thoroughbreds are the only one I know of that insists on having natural mating take place).  If you decide to have your mare bred via AI (artificial insemination), then you may need to choose between frozen semen or cooled, fresh semen.  The costs and breeding statistics differ between the two, so careful consideration needs to be made when choosing.  Which brings us to the costs….

Costs

Costs can add up very quickly when breeding a mare.  For each type of breeding, lets talk about the costs that can surprise mare owners.

Natural/pasture breeding

1)  Trailering to and from the stud – gas, wear and tear on trailer, travel fees (food, hotel, etc).

2)  Mare care at the breeding farm – food, vet care (for injuries, sickness, pregnancy checks).  Mares usually live at the breeding farm until they get pregnant, so if it takes 2 or 3 cycles for her to get pregnant you could be looking at those costs for 2-3 months.

4) Follow up vet care – have your vet make sure the mare is still pregnant.

Artificial Insemination – Frozen or Cooled Semen

1)  Initial vet exams to determine timing of breeding –  Artificial insemination needs to take place very close to ovulation (preferably 24 hours before ovulation) so the sperm will reach the egg soon after it is released.  This requires that a vet does serial ultrasonic evaluations to determine the when the mare is going to ovulate.  Each ultrasound costs money, as does the vet visit.  Often a more money-saving method is to leave your mare at the vet clinic and have them do the ultrasounds and actual insemination when it is time.

2)  Cost of shipping semen – Semen must be shipped overnight to the mare, which can be expensive.  Additionally, each semen collection from the stallion may have its own separate fee.  The breeding contract should spell all of this out.

Horse herds in the wild, such as Chincoteague ponies, have foaling rates from 50 to 75%. Horse owners should not expect 100% of mares to get pregnant the first time trying.
Source: chincoteagueislandvacations.com

For any type of breeding there is always the chance that it takes more than one attempt to get pregnant.  In nature or in wild herds, the average foaling rate is around  50-75%.  That is with multiple natural breedings over a season in a low-stress environment.  Now put the horse in a higher stress environment with semen that has been shipped across the country and the chance that the mare gets pregnant in one try decreases to around 50% or less.  Horse owners often are shocked if their mare does not end up pregnant after one attempt at breeding and are dismayed when they only budgeted for one round of insemination.  A good source for hard data regarding breeding statistics is on the Select Breeders website.

Additional expenses may be incurred depending on the individual mare.  Some mares have immune reactions to the semen, which causes very unfavorable environment for a pregnancy to occur.  Your vet may attempt to fix this reaction with antibiotics, anti-inflammatories, and uterine lavaging.  Other times the mare may need a small surgical procedure to correct vaginal conformation abnormalities.  Hormonal injections may be needed to ensure the mare ovulates within a specific timeframe.  Your mare also may need to be supplemented with progesterone-like hormones to maintain her pregnancy.  Each case is different, so it is best to plan for a flexible budget when it comes to breeding. Breeding horses can become complicated and expensive, which can lead to frustrated mare owners.  Careful considerations regarding the stallion, type of breeding used, and budget planning can go a long way to easing the stress of getting a mare pregnant.  I hope to add more posts regarding the details of artificial insemination and horses, but first I wanted to give a broad overview of the information owners need to be aware of before breeding their mare.

The art and science of a lameness exam

Athletic trainers, orthopedic surgeons, and all the various other professionals involved in human sports medicine have it easy.  Waaaay easy.  When a person has pain when they are doing an activity (running, jumping, etc), they can go into the doctor or trainer and “Here’s where it hurts” and “It hurts whenever I do X activity”.  The doctor can get essential information from the patient in less than 10 minutes simply by asking the right questions and getting detailed, honest answers.

Now lets talk about the difference a veterinarian faces when performing a lameness exam on a horse.  The horse can not tell us which leg hurts, where on the leg it hurts, what activity makes it worse, how long it has been happening, etc, etc, etc.  A veterinarian relies on the owner or horse trainer to gather some of this information, but often the information is vague or conflicting depending on whom you are talking with.  Many times I get some variation of the following history:

“My horse has been ‘off’ for a couple of months now.  It feels like it is in the hind leg but my trainer said she is short striding in the front.  I gave the horse some ‘bute’ but I ran out so I stopped a couple of weeks ago.  My farrier put on shoes last week.”

This type of history is very vague and really does not tell the vet much except this is a chronic mild to moderate lameness.  Now it is up to the vet to figure out what is really going on and how to fix it.

Which leg or legs are lame?

This is the first question the vet attempts to answer when performing a lameness exam.  Sometimes it is very obvious, other times it can hard to tell.  In order to determine which leg or legs are lame, the vet will watch the horse perform different gaits, starting with a basic walk.  If not obvious at a walk the vet will move on to a trot in a straight line.  If it is still not obvious the vet may lunge the horse in different directions and on different surfaces.  Basically the idea is to visualize the lameness or gait abnormality that the owner or rider has noticed.

The vet will watch the horse move at different gaits on different surfaces to help determine which leg is lame.
Source: thehorse.com

Several things can come up that make finding the lame limb difficult or impossible:

1.  The horse is not lame the day of the examination.  This situation happens very often and is a major frustration for owners.  You can have a horse that has been consistently lame for three months but the day the vet examines it the horse will suddenly be sound.  An important piece of advice is to exercise your horse before the vet appointment and make sure his is actually still lame!

2.  Multiple legs are lame.  It is extremely hard to make an accurate diagnosis when a horse has multiple limbs that are making his gait abnormal.  One leg may be compensating for another or the legs may have two completely different issues.

Where in the limb or body is the lameness coming from?

Once the vet determines which limb is lame, the next step is to find where in that limb the lameness is coming from.  Again, sometimes this can be quite obvious.  For instance, if the right front leg is lame and the fetlock is swollen, hot, and painful your vet probably will be confident that the lameness is coming from the fetlock region.  If it is not obvious, your vet can perform certain tests to help localize the lameness.

Your vet may perform a flexion test in order to determine where in the limb the lameness is coming from.
Source: vetmed.vt.edu

One simple test is called a “flexion test”.  Your vet will hold certain joints in flexion for various periods of time and then watch the horse trot.  If flexing a joint makes the lameness worse, it is highly likely that the lameness is coming from that joint.  Another way to help localize a lameness is to test the hoof for sensitivity to pressure.  A hoof tester is a device that puts pressure on certain regions of the foot.  A reaction or pulling  the foot away from the examiner tells the vet that the horse is sore at that particular location in the foot.

If after performing flexion tests, palpating the limb, and manipulating the limb, the location of the lameness is still not obvious your vet make begin “blocking” the limb/joints.  “Blocking” refers to numbing portions of the limb and watching the horse trot. If the lameness disappears after a nerve “block”, then the vet can be confident that the problem area is within the portion of the leg that was numb.  This test does not always pinpoint the exact location of the lameness, and sometimes the results can be questionable – for instance, the lameness might improve by only 50%.  If this is the case your vet may repeat the block on a different day or use a combination of tests to localize the lameness within the leg.

What pathology or abnormality is causing the lameness?

In some cases your horse may need an MRI for accurate diagnosis of the cause of his lameness.
Source: purdue.edu

After your vet is confident that they have pinpointed the lame leg and localized the lameness to a region of the leg, they can begin to look for an abnormality in that region that is responsible for the lameness.  The most common way to detect the abnormality is by using diagnostic imaging (x-rays, ultrasound, MRI, etc).  Depending on the case and the experience of the vet, they will usually start with either x-rays or ultrasound to image the leg.  X-rays are used to visualize bones and joints, whereas ultrasound is better for looking at tendons and ligaments.  Sometimes a defect or abnormality may be very small and impossible to see with x-rays or an ultrasound.  At that point your vet may refer your horse for an MRI or a nuclear scan.  Diagnostic imaging often is the most costly part of the lameness exam.

What can an owner do prepare for a lameness exam?

If a horse owner has never had the experience of dealing with lameness issues, there are several things that I think they should know before having a lameness exam done on their horse.

– Do not give your horse any pain medication (bute, Banamine, etc) at least 48 hours before a lameness exam.  The vet wants to see your horse when it is as lame as possible.  This make localizing the lameness much easier.

– Bring your tack with you and be prepared to ride.  Sometimes a gait abnormality is only visible under saddle.  The vet needs to see the lameness in order to make a diagnosis, so you will need to recreate the situation in which the lameness occurs.

A nerve block numbs portions of the limb. If the lameness improves by 80% or more, it is likely the cause of the lameness is in that region. If the lameness only improves slightly then different nerve blocks may need to be attempted.
Source: research.vet.penn.edu

– The examination may take several hours, maybe even days.  The more difficult it is to determine where the lameness is coming from, the longer the exam will take.  If blocking the leg doesn’t show >80% improvement then it may need to be blocked a different way (for example a joint blocked instead of a region of the leg) to narrow down the source of the pain.  The numbing effect of a block can last hours and the vet needs to be sure that the first block has completely worn off before trying a second one in the same region.

– Lameness examinations can be expensive.  A subtle lameness with a hard-to-visualize abnormality can be very difficult and time-consuming to correctly diagnose.  An owner needs to be prepared that in order to get definitive answers, they may be spending thousands of dollars.  On the other hand, an obvious lameness that is easy to diagnose (example: hoof abscess) will not be so costly.

To summarize….

In order for a veterinarian to be proficient in lameness diagnostics, they must be experienced in the observation of gaits, recognition of subtle abnormalities, interpretation of test results and diagnostic imaging.  The lameness exam is an exercise of both the art and science of veterinary medicine.

Equine Herpesvirus 1 – What you need to know when facing current outbreaks

Outbreaks of diseases are scary.  The disease can be a brand new virus, a bacterial “superbug”, a virus that has mutated, a parasite that has spread to a new geographic location – you get the idea.  The recipe for a contagious disease outbreak calls for two basic things:

Ok, we aren’t talking about an outbreak of zombies, but horse disease outbreaks are scary too!
Source: inkace.com

1) a susceptible population of living things (humans, animals, plants, etc) that do not have immunity to the pathogen

2) a pathogen (virus, bacteria, etc) that is easily transmitted between individuals it infects

The disease does not have to be deadly, its main goal is just to replicate in its host.  For instance, the flu virus is not often deadly but it transmitted very easily between individuals.  This ability allows the virus to find a new host before it is destroyed by the original host’s immune system.  The ease of transmission causes a lot of individuals to become sick in a short amount of time.  Additionally, if the pathogen can replicate in its host, and that individual becomes contagious before they realize they are sick, the disease has an extra advantage.

So how does all of this figure into the current outbreaks of Equine Herpesvirus-1 (EHV-1)?  Well, first I am going to discuss a little bit of background information on this virus (which is not a new virus, by the way).  Then I will delve into how it has evolved to cause current outbreaks of disease.  Finally, I will go over ways horse owners can prevent and prepare for an outbreak of EHV-1.

What is EHV-1?

An electron photomicrograph of EHV-1          Source: Gluck Center at University of Kentucky

EHV-1 stands for Equine Herpesvirus Type 1.  There are several types of Equine Herpesviruses but the main ones that cause serious health problems  in horses are Types 1, 3, and 4.  In this post I am only going to discuss EHV-Type 1.  EHV-1 can cause 4 different manifestations or clinical presentations:

1.  Neurologic – aka Equine Herpesvirus Myeloencephalopathy (EHM).  This form affects the nervous system (brain and spinal cord).

Just to be clear – EHM is a form of EHV-1 – not a separate disease.

2.  Respiratory – Affects the respiratory system (lungs, sinuses, trachea, nasal passages, etc.)

3.  Abortive – Affects the reproductive tract of a pregnant mare causing fetal death and subsequent abortion

4.  Neonatal – Newborn foal is born apparently normal but then becomes severely ill 1-2 days after birth.  Despite the best supportive care these foals often die from severe respiratory disease and it’s complications.

How does EHV-1 affect the horse?

The virus can affect 3 different types of body systems: neurologic, reproductive, and respiratory.  Once a horse is infected with the virus, the virus travels to the lymph nodes and infects certain types of white blood cells.  The infected cells are released out into circulatory system, where they travel in the blood to different sites in the body.  They can travel to the lungs, uterus, or spinal cord.

One key point here is that it is unknown why the virus attacks certain areas of the body.  There is research currently being performed that is attempting to figure out why an outbreak of neurologic disease will affect one group of horses, but another group may only show up with respiratory disease.  One recent finding is that there seems to be some genetic varieties of the virus that tend to cause the neurologic form more often, but not all cases of EHM are caused by these mutant varieties.

How is EHV-1 transmitted or spread?

EHV-1 has several of what I like to call “superpowers”.  The way it is transmitted is one of its superpowers.  Most of the time the virus is transmitted by horse-to-horse contact.  We all know how curious horses like to smell everything and everyone, especially new horses.  In fact, most horses introduce themselves by intensely smelling one other’s nose – it’s like they are smelling each others breath!  EHV-1 (cleverly) is easily transmitted through nasal secretions from one horse to another.

Horses naturally communicate with one another by touching noses and smelling. EHV-1 has adapted so that it is transferred to a new horse when this happens.
Source: thehorse.com

However, EHV-1 has also evolved to be able to survive on the surfaces of objects that are contaminated by an infected horse (tack, human clothing, stalls, fences, etc).  And that’s not all – the virus can live (in the ideal conditions) up to 21 days on an object!  Furthermore, foals can be infected in utero and other horses can be infected by contact with an infected placenta or fluids from the mare.

So I can just keep my horse away from sick horses and he will be fine, right?

Wrong :(.  Another superpower of EHV-1 is that it can infect a horse and the horse can become contagious to others even before it shows physical symptoms of being ill.  By the time you see that the horse is sick he could have already infected all of his pasture mates.

A third superpower of EHV-1 is it’s ability to become latent (dormant).  A horse can be a “carrier” of this virus (a reservoir) and not show any outward abnormalities.  At some point, though, the virus can be reactivated in the carrier horse – who can now spread the disease to others.  Things like stress or a different illness can cause EHV-1 to be reactivated.  It is no wonder that  weaning, training at the racetrack, and traveling for shows are common times where we see outbreaks of EHV-1.

What about vaccines?

Vaccination is an excellent way to prevent spread of EHV-1 and has worked wonders for the breeding industry in preventing abortion outbreaks.  It also seems to protect against respiratory disease.  However, there is no current vaccination that is able to completely prevent the neurologic form of the disease.  This is a hot area of research and scientists are working on ways to improve the current vaccines or possibly manufacturing new vaccines to protect against EHM.

Source: The Gluck Center at the University of Kentucky

EHV-1 has been around for a long time.  Why the big concern about it now?

The concern over the recent outbreaks has to do with the fact that EHM (caused by EHV-1) is an emerging disease.  The neurologic form of EHV-1 (EHM) used to be quite rare.  However, in the early 2000’s we started to see outbreaks of horses affected with EHM in various spots across the US and the world.  The virus has seemed to change in its severity and/or behavior in affected animals.  Furthermore, since vaccinations do not protect against this form of the virus, there is no way to systematically control it.  And remember how easily it is spread (its superpowers)?  The fact that the virus can spread to hundreds of horses without seeing a single horse look sick makes it a big cause for concern.

What are the clinical signs of EHV-1 and EHM?

The signs listed in the tables above are seen with lots of diseases – not just EHV-1 or EHM!  One important characteristic is that your horse needs to have made contact with new horses or their bodily fluids, and that the onset of the neurologic signs is very fast.  Usually the signs show up and progress for 24-48 hours and then stop progression.  After that 48 hour period, the worst appears to be over and how bad each individual horse is affected will determine their prognosis.  If the horse goes down and can’t get back up then the prognosis is grave.  If the horse is only minimally affected then the odds are good that they will gradually recover.

What about treatment?

There is currently no specific treatment for EHV-1 and EHM.  Because they are viruses, antibiotics will not fight them.  However, sometimes horses are given antibiotics to prevent opportunistic bacterial infections because the horse’s immune system is working overtime on fighting the virus.

There is no specific treatment for EHV-1 and EHM, so we rely on supportive treatments (like IV fluids) assist the horse in its recovery.

The treatments your horse will receive are all supportive – meaning they are just supporting his basic bodily functions until his immune system takes care of the virus and healing takes place.  Examples of supportive treatments are IV fluids and anti-inflammatory drugs.

How can I prevent my horse from getting EHV-1 or EHM?

Even though the vaccine does not specifically protect against the neurologic form of EHV-1 (EHM), it is still a good idea to vaccinate your horse for EHV-1.  The vaccination does protect against the respiratory form and the abortive form of EHV-1, so your horse will be protected against those manifestations of this disease.  The vaccine does also seem to decrease viral shedding, so if your horse does become infected with the neurologic form you can help prevent shedding and infecting other horses with the virus.

Another was to prevent EHV-1 and EHM is to practice good biosecurity around the farm.  This means that any incoming horses are isolated from your herd for a period of at least 21 days.  That means that nothing that the isolated horse touches is allowed to touch anything that your herd horses may touch (tack, buckets, stalls, fences, etc).  Wash your hands between caring for your new horse and the rest of the herd.  Take the temperature of the new horse twice daily to make sure he does not spike a fever.  Isolating new horses protects against many diseases, including all the forms of Equine Herpesvirus and Strangles.

Horses that travel to shows or clinics should also be isolated from your herd when returning.  It is a good idea to take the temperature of your horse twice daily for 14 days before returning him to the herd.  If he develops a fever, call your vet.

There is a ton of information on the internet regarding what happens if your horse is at a show when there is an outbreak and various scenarios of the like.  Sources that are reputable include AAEP and APHIS.USDA.gov.  Another thing you can do is call your vet and see if they know about any current outbreaks in the area.  And it is never a bad idea to contact the shows and places you are traveling to see if they know of any outbreaks or precautions you should take to protect your horse.

Equine Corneal Ulcers – The Case of the Squinty, Watery Eye

Imagine that you are going out to feed your horses for the evening and you notice that one of them is holding her eye shut.  It looks pretty swollen and there is a bunch of watery discharge coming from the corner of the eye.  You put her in the cross ties and try to pry her eye open to have look at the eyeball, but those darn eyelids are so strong!  Finally you result to just standing there are staring at her, waiting for her to open the eye.  When she finally does, you notice the eye looks cloudy.  Time to call the vet……

Swollen, teary eyes that have a blue or cloudy tinge should be examined by your vet ASAP.
Source: oceanstateequine.com

What could be going on with this eye?

The cornea is the clear tissue that covers the surface of the eye. This is a diagram of a cross-section of the eye.
Source: thehorse.com

When a vet is presented with a horse that has a squinty and watery eye, we can assume that the eye is causing pain to the horse.  A cloudy eye usually indicates that there is “corneal edema”.  The cornea is the tissue on the surface of the eye that is normally clear/transparent.  When the cornea is damaged or irritated is becomes swollen, which creates a blue/cloudy tinge to the surface of the eye.  Corneal edema is not specific for any one disease or injury – it just means that the cornea is injured/irritated.  So the only information we have right now is that the eye is painful and the cornea is swollen.

What happens next?

Your vet will examine the eye.  This may take some sedation, depending on how the horse is behaving.  In some cases the vet may even “block” the eye, meaning they may use local anesthesia to numb the surface of the eye and eyelids as well as prevent the eyelids from squeezing shut.  You would be surprised how crazy strong those eyelids are – I am not kidding.

When doing an eye exam it is best to have the horse in a DARK quiet area.  It may seem counterintuitive, but it is much easier to examine the eye using an ophthalmoscope in the dark than in bright daylight.  Your vet will look through the ophthalmoscope to see the surface of the eye and possibly the back portion of the eye.

Your vet also will most likely stain the eye at this point.  A particular stain, fluorescein, is used to detect defects in the corneal tissue.  In the normal cornea the stain will not attach to the eye because of the surface of the cornea is covered by cells that don’t allow the stain to penetrate them.  If the cornea is damaged or ulcerated the underlying cells of the cornea (stromal cells) will be exposed and they will take up the stain.  The vet can now see where the cornea is ulcerated or damaged.

Fluorescein eye stain can show the location and size of a corneal ulcer.
Source: ckequinehospital.com

If no stain taken up by the eye, the vet will then have to look for other possible reasons to explain why the cornea is swollen.  For the purpose of this article, however, let’s say that your horse had an area of stain uptake of about 2mm diameter.  Your vet now can be confident that a corneal ulcer is responsible for the clinical signs your horse is exhibiting.

How is a corneal ulcer treated?

Like many things in medicine, the answer is “It depends.”  In this case it depends on how deep the ulcer is, how long it has been going on, and how the ulcer responds to initial treatment.  In most cases of a simple ulcer that is caught early in its progression, treatment consists of topical antibiotic ointment, anti-inflammatory medication, and topical atropine.  In other, more complicated cases your vet may want to use additional medications like topical anti-fungals and serum.  In any case, do not use over-the-counter eye medication on your horse!  Do not use Neosporin in the eye!  The eye is VERY sensitive and needs ointment specifically designed to be applied to the eye.

Most of the time the topical medications are applied several times a day to the affected eye.  The constant manipulation of the eye can lead to a very cranky horse.  Sometimes owners will have such a difficult time with their horse that the medication never properly gets in the eye and the eye doesn’t heal.  In these cases there is a special medication delivery system that can be placed around the eye so that the medication can be applied without having to manhandle the horses eye.  The subpalpebral lavage system is definitely something to ask your vet about if you are having difficulty getting eye medications into your horse.

A subpalpebral lavage system allows medication to be administered through a syringe, where it travels down a tube and is deposited under the upper eyelid.
Source: veterinare-ophtalm-lengelle.be

Finally, your horse will need to be kept out of daylight if she is receiving atropine topically to the affected eye.  Atropine forces the pupil to dilate, which is beneficial is terms of preventing pain and permanent damage to the eye.  However, the eye will not be able to adjust to light (by constricting the pupil), so your horse will need to either be in a dark stall or have a patch placed over the affected eye.  Once the atropine is out of the system, the horse can return to her normal turnout schedule.

How long does it take to heal?

Ulcers not treated properly can become infected with bacteria and/or fungi. Infected ulcers take months to heal and can have major complications.
Source: northfloridaequine.com

A normal, uncomplicated ulcer should heal within a week or two.  Larger and deeper ulcers take longer to heal than small ones.  Ulcers that become infected with bacteria or fungi can take months to heal.  There are also “indolent” ulcers, which are ulcer that just seem very resistant to healing despite all therapies.  These are fairly rare.  The most important thing to remember is that early recognition and treatment can save you weeks of treatment and loads of money in the long run.  The “wait and see” approach is never a good idea when it comes to the equine eye.  There are several cases each year of clients who end up spending a lot of money treating an infected ulcer for months because they wasted three days treating the horse with an over-the-counter medication.

Any prevention tips?

There is no possible way to 100% prevent the equine eye from getting injured – sorry.  But, keeping a vigilant eye out for areas that look like a good place to scratch or poke an eye can help.  Nail heads, chipped wood, or any piece of wire hanging around is an easy place for a horse to injure his eye.  Also, horses can get ulcers even if they have on a fly mask, so make sure to take off the mask every day and look at the horse :).

Vaccinating Your Horses – What, When, and Why?

For an equine vet, springtime is extremely busy – foaling, breeding, vaccination, Coggins, etc.  Our clinic typically vaccinates over 100 horses per week from March until May.  That’s a lot of vaccinations!

Some vaccines are recommended for all horses, others just for “at risk” horses. Each horse should have a tailored vaccination program designed by your veterinarian.
Source: thehorse.com

I would like to write about this topic today because recently there have been outbreaks of diseases that could have been prevented or mitigated had the horses been vaccinated.  Additionally, because medical topics that affect humans (such as vaccination risks vs. benefits) often trickle over into vet medicine, I would like to address the risk vs. benefits of equine vaccines.

The recommendations for vaccinating in this post are taken from the American Association of Equine Practitioners Vaccination Guidelines.  As always, please discuss vaccinations for your horses with your personal vet for reasons you will learn about as you continue to read.

What Vaccinations Should My Horse Receive?

It depends…..

Several factors to consider include:

1.  The job of the horse

Some diseases that we vaccinate for are transmitted from horse to horse.  Others are transmitted to the horse from other animals.  Still others are contracted from the environment.  Horses that stay on the farm the majority of the time and rarely come into contact with other horses have a low risk of picking up diseases that are communicable.  In contrast, horses that are going to clinics and shows every weekend have a high risk of picking up these type of “bugs”.

2.  The location of the horse:

Different areas of the United States, and other countries for that matter, carry different risks for picking up particular pathogens.  For instance, Potomac Horse Fever is not prevalent everywhere in the US.  Some areas, such as the mid-Atlantic region, carry a very high risk for PHF yet other areas have relatively low risk.

3.  The health status, age, and medical history of the horse:

There is always a risk with vaccinating horses, as with anything you put into their body that is foreign (medication, food, etc).  Some horses are prone to vaccine reactions, which may include fever, lethargy, anorexia, and swelling of the vaccination site.  For these “sensitive” equids we try to only vaccinate with the bare essentials.  Additionally, different age groups of horses have higher risk of contracting specific diseases, so sometimes vets will recommend a vaccination for a young horse but not your geriatric horse.

4.  Recent disease outbreaks:

Disease outbreaks scare all of us and can lead to widespread panic amongst horse owners.  Couple that with the misinformation gained from social media and suddenly vets are receiving dozens of phone calls from frantic horse owners wanting their horse immediately vaccinated for X,Y, and Z.  This week there was a confirmed case of EHV-1 at Michigan State University in a barrel horse.  Two days later we are getting calls from people asking if they should not take their horse to any barrel races in the near future.  Cases like this can be scary, but it is very appropriate to discuss the risk of these diseases with your vet before vaccinating your horse.  Your vet will be the best source of information regarding any recent disease outbreaks in the area and if your horse should be vaccinated.

Map of EHV-1 Myeloencephalitis cases from March 2014 to March 2015. Your vet can help you decide what vaccines are appropriate based on recent disease outbreaks.
Source: wormsandgermsmap.com

Even though some vaccinations may not be necessary for your horse, there are a few vaccines that are considered “core” – meaning all horses in the US should receive these vaccines.  At a bare minimum the AAEP recommends all horses get vaccinated for:

– Tetanus

– Eastern and Western Equine Encephalomyelitis (EEE and WEE)

– Rabies

– West Nile Virus (WNV)

Risk-based vaccines are administered based on each horse’s particular risk for contracting the respective disease.  Some risk-based vaccines are:

– Potomac Horse Fever

– Strangles (Streptococcus equi)

– Equine Herpesvirus Type 1 and 4 (EHV-1, EHV-4) a.k.a Rhinopneumonitis

– Equine Influenza

– Botulism

For more details regarding each of these vaccinations and their recommendations, please visit the AAEP Vaccination Guidelines page.

When Should My Horse Get Vaccinated?

Many diseases are transmitted by insects, which are seasonal depending on where you live. Your vet will help you decide the optimum timing for your horse’s vaccinations.
Source: ocalapost.com

For most vaccines it takes two weeks to develop immunity or protection from disease.  That means your horse should be vaccinated a minimum of two weeks before he needs protection.  Many of the diseases we vaccinate for are transmitted by insects or mosquitoes (PHF, EEE, WEE, WNV), so we recommend vaccinating a short time before these insects are active, and repeat yearly.  additionally, for communicable diseases such as Equine Influenza, your vet may suggest a second vaccination in the autumn if your horse will continue to travel through the winter.  It is less than ideal to wait until July or August to vaccinate your horse because insects will have already been active and could transmit disease before then.

Why Should My Horse Get Vaccinated?

My guess is that your horse is more than just an animal to you.  He or she is probably your companion and you love them.  Because you love your horse, you would not want to see him sick.  Many of the diseases we can vaccinate for are not pretty to see.  I know many horse owners who feel guilty if there horse gets injured or sick, even though there is not way they could have prevented it.  Imagine how it would feel to know that a horse is sick but it could have easily been prevented.

Vaccines are rigorously tested and inspected before being allowed to be administered.  This is to ensure their safety and effectiveness in preventing disease.  Although the rare horse will have a reaction to a vaccine, by far the majority are mild and temporary.  So yes, there are risks with giving a vaccine, but the benefits (protection from deadly disease) are greater.

Finally, the cost of treatment FAR surpasses the cost of a vaccine.  For instance, a vaccine may cost anywhere from $15-80 plus any additional services or fees.  An emergency call for an acute neurologic disorder may run you into the $1000’s in just one night.

Veterinarians are not doing the job for the money.  We are not pushing vaccines to try to please “big pharma” and get fancy rewards from drug companies.  I know conspiracies are interesting, but honestly, we make very little money in administering vaccines to horses.  It is not fun to spend the day jabbing horses with needles and giving injections.  We just want to keep your horse healthy and happy – like you!

Understanding seasonal cycles in mares

First I want to apologize for not posting last week, but I was on vacation and out of the country.

Second, since today is the first day of Spring, I figured it would be a good time to help mare owners understand their horse’s seasonal reproductive cycles.  I also aim to describe what behavior changes to look for in your mare, as well as help you understand what methods are available to help modify behavioral issues in mares.

Mares = Seasonal Polyestrous

Animals go through what we call “estrous cycles”.  This means they only are sexually receptive at certain times.  In contrast, human females go through “menstrual cycles”, but are sexually receptive throughout the cycle.  The estrous cycle can be fairly complicated and differs greatly among animals.  For simplicity, I will just discuss the estrous cycle of the horse.  For comparison with other species, visit the Wikipedia page on the estrous cycle.

The yearly cycle of the mare. During the winter months the ovaries are “dormant” and the mare does not have estrous cycles.
Source: myhorseuniversity.com

Mares have what I like to think of as 2 types of estrous cycles – a yearly cycle, and within that yearly cycle, a monthly estrous cycle.

Yearly Estrous Cycle

During the winter months, when there are few hours of daylight, the mare is in the portion of her yearly cycle termed “anestrus”.  During anestrus the ovaries are inactive and the mare does not go through her estrous or “heat” cycle.  As daylight hours increase in the spring and summer the ovaries become active again.  The mare will now have ~21 day estrous cycles throughout the long spring/summer/early fall.  Thus, the term “seasonal” (spring/summer/early fall) “polyestrous” (many cycles).

Monthly Estrous Cycle

Once the mare’s ovaries are active in the spring, she will develop a follicle(s) on her ovary(ies) and release an egg(s) about every 21 days.  These 21-day cycles are each called an estrous cycle (I know, its very confusing!) or a “heat” cycle.  The mare is only sexually receptive to the stallion during the phase of the estrous cycle known as “estrus”.  I am not sure why the two terms “estrus” and “estrous” have to be so similar and confusing, but thats how it is folks.

The 21-day estrous cycle is repeated while daylight hours are long enough to cause the ovaries to be active. Behavioral estrus is also termed “heat” and is the period of time when mares show outward behavior changes indicating they are ready to be bred.
Source: extension.org

Behavior Changes During Estrus

For about a week (1-7 days) most mares will show outward signs of heat.  Some are very demonstrative, others barely show any changes.  The behaviors seen during estrus are there to alert to the stallion that the mare is receptive to breeding and will not kick his head in when he comes looking for love.  These estrus behaviors include:

– increased urination frequency

– holding the tail to the side or constantly lifting the tail

– “winking” of the vulva, especially after urination

– extra sensitivity to touch and stimuli

– unpredictability

– squatting

– decreased eating and drinking

– excitable, restless, “running the fences”

– increased vocalization and squealing

The video embedded below shows typical estrus behaviors in mares.

Modifying and Preventing Estrus Behavior in Mares

Many of the above behaviors are not exactly helpful for performance and show mares.  Some mares have such drastic behavior changes that they can become a danger to their riders and handlers.  In these cases, many clients turn to their vet for help.

Some of the methods used to suppress unwanted estrus behavior in mares include intrauterine marbles, synthetic progesterones, oxytocin administration, and surgical removal of the ovaries.

The logical way to prevent estrus behavior is to prevent estrus all together.  How is that accomplished?  Several methods are available to horse owners, some more drastic and permanent and others temporary.  There are actually many options for estrus suppression, lots of them still experimental, and I am not going to go through them all.  To simplify things, I will state that there are two basic proven ways to stop estrus in the mare.

Method #1:  Trick the body into thinking it’s pregnant (aka the birth control method)

Basic principle: Progesterone is the hormone produced by the body when there is a pregnancy. When progesterone levels are adequate, the body stops going through reproductive cycles until progesterone levels drop (not pregnant). In the mare, once an egg is ovulated a structure forms on the ovary called the corpus luteum. The corpus luteum produces progesterone, which prepares the mare’s body for pregnancy. If the mare becomes pregnant the corpus luteum stays intact and continues to make progesterone, which stops the reproductive cycle from continuing.

Method #2:  Remove the source of the hormones (ovaries) surgically

Basic principle:  The ovaries are the main source of the hormones (estrogens) thought to be the cause of estrus behavior in mares.  Just like removing testicles causes stallion-like behavior to cease, the removal of ovaries should theoretically cause estrus behavior to stop.

Like many issues in medicine and reproduction, there is not a one-size-fits-all solution to the problem with estrus behavior in mares.  One point that I must emphasize, however, is this:

DO NOT JUMP TO BLAMING BAD BEHAVIOR ON HEAT CYCLES!!!!!!!

A mare’s bad behavior can not always be blamed on her estrus cycle!
Source: thehorse.com

In order to determine if estrus suppression will even help with issues regarding your mare’s behavior, there must be a clear and scientific correlation between unwanted behavior and her estrus cycle.  My first piece of advice is to get a calendar dedicated to tracking your mare’s behavior and her heat cycles.  Write down every time you see her show a sign of heat as well as when she is behaving abnormally.  Then, when she is at her worst, have your vet ultrasound her ovaries to confirm that she is in heat or estrus.  If you show your vet your calendar of behavior and cycles, along with the reproductive examination, your vet will most likely be able to determine if there is a strong correlation between her behavior and her cycle.  At that point your vet will recommend a course they deem appropriate to help curb unwanted estrus-related behavior.

If there is no correlation, though, then I suggest working with a trainer to help correct these behavior problems.

Hope you are all having a wonderful spring day so far!

Winter Weight Loss

No, this is not an article about how to shed those winter pounds before spring break.  Despite hours of working out and dieting, it seems that some of us humans are meant to keep a nice winter layer of fat.  That probably was great for our ancestors who worked outside, did physical labor, and risked running out of food during the winter.  It is not so great for our sedentary, modern warm life today – but I digress.

This chunky pony has stored up plenty of fat to use as energy and insulation. However, he still needs to lose weight!
Source: thehorse.com

Like the humans of times long ago, horses that can pack on weight before winter generally fare better than their skinnier counterparts.  The fat keeps them insulated and can be converted to glucose for energy (and thus heat production) when food is not available.  Well-muscled horses also do better than thin ones in the winter, so please don’t think I am just advocating horse obesity.  But, the point I am trying to make is that winter is hard on horses – especially the thin ones and old ones.

This thin horse is going to have more difficulty maintaining his weight during the winter because he is already starting out thin.
Source: gravenhorse.co.uk

What makes winter so difficult for horses?

The number one issue I see for horses in winter is colic, mostly due to dehydration.  In a previous post (Making Horses Drink), I have discussed how to encourage your horse to drink when it is cold outside, so I am not going to go over that now.  But, I do want to mention that the horses may not feel the need to drink when they are not sweating or active like they are in summer.  So this is one way that winter can be hard on a horse.

Heat is a by-product of digestion. Fermentation of fiber (like hay) releases more heat than simple digestion of grains. This is why it is important to feed hay in the winter!
Modified from: equisearch.com

Another major problem is the cold.  Horses use several tricks to keep themselves warm in the frigid temps.  One way they stay warm is by growing extra hair (a “winter coat”) which can trap air near the body and create insulation.  Another method is metabolism.  Horses that eat hay generate lots of internal heat as they metabolize their meal.  Digestion of grain does not generate much heat  in this aspect because it is digested much faster and easier than hay.  Hay undergoes fermentation in the cecum and colon, which serves as an excellent internal heater.

Air from outside is warmed by the body and trapped close to the skin by long winter hairs. This is one way horses stay warm outside.

The methods horses naturally use to stay warm in the winter can fail though.  If their coat gets damp they can become chilled.  Left outside without hay to munch on can also lead to problems.  Once a horse gets cold, a downhill cascade may begin with the ending being a down horse (see post on “The Dreaded Down Horse” for more details). Finally, ice and snow can cause footing to be hazardous.  Last week I had to put a horse to sleep that had completely fractured its upper femur when it slipped on the ice and snow :(.

Why do horses lose weight in the winter?

Like discussed above, metabolism is a very important way that horses stay warm when the temperature drops.  Metabolism refers to the production of energy from the digestion of feed.  To create more heat, metabolism is increased, which means food is digested and used up at a higher rate than normal.  Think of digestion like a fire.  When you add wood (i.e. food) to the fire, the fire generates more heat.  As the fire generates more heat, it takes more wood to continue to keep the fire at the appropriate level.  Simply put, horses generate heat by increasing their metabolism, which means that they require more calories in cold weather than in warm weather.

Because heat production demands are increased in the winter, food intake must also increase or there will be weight loss.

Because their metabolism is ramped up, unless their caloric intake is increased your horse will be burning more calories than he is eating.  This situation leads to weight loss.  Other things that may also contribute to weight loss include poor dentition, competition for food, and lack of mobility.  If a horse has dental abnormalities they may not grind their food to the appropriate size for maximum digestion.  Furthermore, hay is harder to chew than nice soft moist grass, so they may not eat as much forage as they do during the growing season.  If a horse is in a herd situation they may find themselves competing to get to the hay pile or feeder, whereas when grass is available in the pasture everyone can spread out and eat at their leisure.  Finally, horses that are arthritic find moving more difficult when the weather is cold.  They may choose to stay put rather than walk over to the food in order to avoid the pain associated with arthritis.

How can winter weight loss be prevented?

1.  Regular examination – Examine your horse carefully regularly.  Brush him and feel over his ribs and hip bones.  You should be able to feel his ribs at the widest part of his barrel and the hip bones should not be prominent.  If you start to feel his spine protrude, then he is very underweight.  Better yet, get a weight tape and take a weekly weight.  This will give you a nice set of data that you can compare and review to look for trends in weight gain or loss.  And please, if you blanket your horse – take off the blanket and look at the horse regularly!

2.  24/7 Hay – Keep hay available to your horse 24/7 in the winter.  It does not have to be the richest hay, but it should be palatable and soft if possible.

Horses who are outside battling the winter elements should have access to hay 24/7 to keep their internal heaters going.

3.  Dental check-up in the fall – Have your veterinarian do a comprehensive dental examination every fall before your horse starts to lose weight.  Your horse may need some dental work before the winter season hits.

4.  Increase the caloric intake of geriatric horses – Geriatric horses have a particularly hard time in the winter and tend to lose weight more easily than their younger counterparts.  Under the direction of your vet or horse nutritionist, gradually increase the grain and/or feed your older horse receives on a daily basis.  They may recommend certain supplements or additives to increase his caloric intake without having to add a lot of bulk.  One recommendation I give is to begin adding a 1/4 cup of corn oil to the feed.  However, please call your vet and discuss diet changes before adding anything to the feed!

How can I help my horse gain weight?

If you have noticed that your horse is looking too thin the first step is to weight-tape him.  Write down what he weighs and the date.  Then you should call your vet or equine nutritionist to formulate an ideal diet catered to your horse.  Some commonly used supplements/feed that can assist in adding weight to your horse are as follows.

1.  High-quality hay

2.  Beet pulp

3.  Senior feed

4.  Corn oil

Again, please call your vet to discuss ANY diet changes you plan on making for your horse.  There may be an underlying condition present in your horse that could worsen with specific dietery changes.  For instance, if you have an HYPP positive horse you do not want to give them a bunch of alfalfa hay because the high levels of potassium in the hay could exacerbate his condition and lead to a “tying-up” episode.

To cut or not to cut? That is the question (when it comes to colic).

This is the time of year where we see an over-abundance of colic cases in the north.  This past weekend I saw 3 colic emergencies – 2 of which needed surgery to survive.  Despite “colic” being a common malady in horses, there are many misunderstandings regarding this disorder/disease and how it can or should be treated.  When presented with a case of colic the most important question the veterinarian has to answer is whether the cause of colic can be treated medically or if surgery is necessary.  “Colic” is too general of a term to go over in one post, so in this post I will just try to explain how your vet decides if the horse needs surgery or not.

Quick review – what is colic?

“Colic” is a general term for abdominal pain, meaning any organ or place in the abdomen may be causing the pain (stomach, GI tract, liver, etc.).  When we see a horse showing the signs of colic the only thing we know for sure is they have some pain in the abdomen.  The challenge to the veterinarian is to see where the pain is coming from and what is causing it.  For this post I am only going to discuss gastrointestinal causes of colic.

Certain disorders that cause colic symptoms are more common than others, and there are clues your vet uses to deduce which is the most likely culprit in each horse they examine.  Some important factors your vet considers are the horse’s history, age, diet, environment, and breed.  For instance, if I am out to see a colic case where a horse lives on sandy soil with little pasture I will be very weary of a sand impaction.

What is the difference between medical and surgical colic?

A “medical colic” refers to a case of colic that can be treated with medicine and supportive care, whereas a “surgical colic” requires opening the abdomen surgically and physically correcting the problem.  Let’s think of the horses’ GI tract as a hose, with water coming in at the mouth and exiting out through the rectum.  If suddenly the water stops coming out, naturally you are going investigate to determine why the flow has stopped.  If the hose got plugged up with debris you may be able to clear the debris using various chemicals or hot water to break up the plug – this is similar to an impaction colic that can be treated medically.  However, if all of your remedies did not work and the hose was about to burst, you may decide to open that section of the hose and physically remove the debris before repairing that section of hose.  The second scenario is like an impaction colic that needs to be treated surgically.

Like a twisted hose, the intestinal tract must manually be rearranged during surgery. No amount of medicine will correct this abnormality.
Source: medicaldictionary.com

Still using the hose analogy, let’s say that the hose got twisted up and kinked, and thus stopped running.  No amount of chemicals or hot water that you try to put through the hose will fix that kink and twist.  The only way to correct the problem is to manually untwist the hose and put it back in place.  This scenario is like a displacement or twist of the GI tract, which can only be corrected with surgery.

How do you know whether a colic case needs surgery?

The general physical exam will help your vet figure out the severity of the colic case.  Rapid heart rate and sweating can indicate severe pain.  Dry mucus membranes tells the vet the horse is dehydrated.  The absence of GI sounds can indicate that the bowel is not functioning.  Aside from the physical exam, there are other tests your vet uses to determine if your horse needs surgery or not.

1.  Response to pain meds – The most important way your veterinarian determines whether your horse needs surgery is by his response to medical therapy and pain medication.  If the pain is not controllable despite strong painkillers and anti-inflammatory medication, then something is not right inside and there is a high probability that it can only be fixed with surgery.

The rectal exam allows for the vet to make sure things are in the correct position and to feel for impacted bowel.
Source: peasebrookequineclinic.com

2.  Rectal examination – When your vet puts on a long plastic glove and squirts a bunch of lube on it, it can only mean one thing :)!  However gross it may be to some individuals, it is an important tool that lets us palpate a portion of the GI tract and abdomen which cannot be seen with an x-ray or ultrasound.  We may be able to feel a hard, impacted colon, indicating the possibility for medical treatment.  Other times we may feel like all of the GI contents are pushed to one side, indicating a displacement which most likely needs surgery.

3.  Reflux (vomiting) – A horse physically can not vomit like humans and dogs and cats because of their anatomy.  The sphincter muscle that closes when something enters the stomach is very strong, plus the esophagus enters the stomach at an angle which makes it hard to push the contents back up into the esophagus.  So when the stomach contents are not emptying into the rest of the GI tract they start to accumulate in the stomach and cause it to stretch (which in turn causes pain).  If this happened to us humans we would just throw up to relieve the pressure, but the horse can not do this.  This is why the vet will stick a tube down the horse’s nose and into his stomach, which essentially allows for the stomach to release its contents orally.  The reason that this treatment/diagnostic test is so important is it give us a clue as to how long the problem has been going on and how severe the blockage has become.

“Reflux” of stomach contents indicate contents are not moving through the GI tract.
Source: chinovalleyequine.com

There are many other tests that a veterinarian can use to determine the necessity of surgery, but the top three listed above are the simplest and most direct.  However, until we actually open up the horse we can’t say if the colic would have gotten better with surgery or not.  Because of this most veterinarians will give you probabilities when it comes to determining how to treat a colic.  For instance, one case this weekend could not be controlled with pain medication and had a rectal exam that indicated there was a major displacement of the GI tract.  I could not say that I was 100% percent sure that the horse needed surgery to survive (nothing in medicine/surgery is 100%), but I did say I was 99% sure that was the case.  In another case the horse responded OK to the pain meds, had a normal rectal exam and no reflux.  Because he still was a bit painful despite medication, we kept him in the hospital for IV fluids and observation.  At that point all I could tell the owners was that he was most likely going to be fine but I wanted to make sure he was pain-free before sending him home.  After 3-4 hours he appeared fine, wanted to eat, and passed feces, so off he went.

I hope this post makes it a bit easier for the reader to understand how vets know when to send a horse to surgery and why some colic cases need surgery but others don’t.

Please feel free to email me with questions or future topic requests!