Equine Vaccine Tips and Strategies

Written By: Dr. Tom Schell

If you own a horse, one of the most important things you can do to maintain health is vaccinations, but it can also be a costly endeavor.  Everyone seems to have a strategy or recommendation, but the question is 'what is right for your horse?'.  Well, that depends on many factors including location, exposure to other horses as well as general risk factors.  Another thing to consider is that vaccines are not without harm and over administration of vaccines can prove to be harmful in some circumstances.  Let's explore the options and recommendations.

When viewing vaccines and establishing a protocol, we must remember that each horse is an individual and that no one perfect protocol exists.  It is also not generally necessary to implement the same protocol in every horse just because they are in the same barn.

Here are the main points we should consider when establishing a vaccine protocol:

• Risk factors associated with the particular horse (including housing, exposure to other horses, environment, age and geographic location)
• Impact of the particular disease we are targeting including mortality/morbidity rate and risk of spread to other animals and species (including humans)
• Possible negative side effects of vaccine
• Cost implications to the owner
Some basic considerations that we always need to remember include:
• No vaccine is 100% effective in preventing disease
• Vaccines are designed or intended to reduce morbidity or clinical signs of disease
• No vaccines is 100% safe and risk free
• Vaccines are not generally protective until 10 days or greater post administration
• Most vaccines require an initial booster series to build an antibody titer and establish protection
• Many vaccines come combined with many antigens

So, now let's start with the basics in terms of equine vaccines.  In most cases, we generally have the core or basic vaccines, as defined by the AAEP.
1. Tetanus  (annual vaccine)
2. Rabies     (annual vaccine)
3. Eastern/ Western encephalomyelitis (annual vaccine in spring)
4. West Nile  (annual vaccine in spring)
After the core vaccines, we then have what is called 'risk based' vaccines which include:  (Based on AAEP Guidelines)
1. Influenza  (annual to biannual vaccine)
2. Rhinopneumonitis (EHV)  (not necessary, annual or biannual dependent on situation and in pregnant mares)
3. Potomac Horse Fever  (not necessary, annual, biannual or more frequent dependent on situation)
4. Strangles  (not necessary, annual or biannual dependent on situation)
5. Rotavirus  (pregnant mares at 8,9,10 months gestation)
6. Botulism  (annual and one month prior to foaling)
7. Anthrax  (annual vaccine)
8. Equine Viral Arteritis  (check with state guidelines)

In most cases, the core vaccines are vital and given to every horse.  The big question comes as to what other risk factors are involved, which determines if other vaccines are necessary.  Such risk factors include exposure to other horses such as boarding facilities, traveling and competition, but also include issues concerned with breeding operations.  We always have to remember that not every horse responds appropriately to the vaccines, meaning that some develop protective titers while others do not.  In larger facilities, it is generally easy enough to keep most if not all of the horses on the same protocol due to ease of record keeping, but also by doing this we can hopefully minimize disease prevalence and thereby protecting those other horses that may not be responding to the vaccines appropriately.  We also have to take into consideration age of the animal at the time of vaccine as older horses tend to be less predisposed to various illnesses such as EHV, which according to the AAEP is less frequently seen in those horses over the age of 5, unless we have other known risk factors included such as a breeding operation or frequent movement of animals.

How are vaccines administered and how often?

In most instances, vaccines are administered by intra-muscular injection, usually in the neck region, pectorals or the thigh muscle.  Some vaccines, such as Strangles, Influenza and some EHV vaccines may be administered intra-nasally. In adult horses that are unvaccinated, it is generally recommended that they receive at least a 2 injection series, spaced apart by 4-6 weeks.  In foals, vaccines are generally started around 3 months of age and given as a series of 3 injections spaced 4 weeks apart.  Pregnant mares are generally advised to receive a full 'core' vaccine series about one month prior to foaling in order to help build passive transfer for the foal.  Other vaccines such as EHV are given at specific intervals during the second and third trimester.  Most of the core vaccines, once initiated, are administered on an annual basis.

What are the side effects to the vaccines?

No vaccines are completely safe nor void of any risk!  That being said, most vaccines are administered without any problems but the most common side effect seen is general malaise, body aches and a slight fever 24-48 hours after administration.  Dependent on where they were given, we will often see sore necks and even swollen injection sites.  In most of these cases, the signs resolve within a couple of days with no harm to the horse.  It is generally not advised to compete or even work the horse for a couple days post vaccine due to side effects noted.  Some vaccines are more prone to developing side effects than others and in my experience, the Tetanus and Rabies vaccine are the most common.  Vaccines that are administered by the intra-nasal route commonly produce a mild sneeze or even slight clear drainage for a couple days post administration.  In more severe cases, a non-steroidal anti-inflammatory medication may be administered to help alleviate the clinical signs.
More serious or adverse reactions have been noted included anaphylactic reactions (some life threatening), localized infection, scar tissue deposition generalized hypersensitivities.

Why do some horses respond differently to the vaccines?

We have to determine what is a favorable response to a vaccine?  Ideally, it would be one void of any side effect and one that establishes a protective antibody titer.  In most instances, the horses do respond well to the vaccines and without any side effects, but determining the proper antibody titer is difficult to do in most cases.  In the ideal world, we would perform antibody titers to determine who is and who is not responding well to the vaccines, which might help us to focus on more in need horses, but this is costly.

Given, in my experience, that 9 out of 10 horses respond with no noted side effects, the question comes as to why that 10th horse reacted negatively.  Did they have a reaction to the vaccine?  What was that reaction?  A fever, general malaise or worse?  I really begin to question things when I have vaccinated a particular horse routinely year after year, using the same vaccine brand, and yet, this horse reacts negatively.  We can speculate, but really we don't have any pinpoint answers.
In the world of small animal veterinary medicine, we almost always perform a basic physical exam prior to the administration of vaccines.  The purpose of the physical is to pinpoint any health problems and determine if there is any fever present, which may also indicate a health concern.  In the world of equine veterinary medicine, the individual physical exam is performed but not that often, especially on larger farms due to time constraints and cost.  Often, the vaccines are administered one horse at a time while working the way down a barn isle way.  The horses are often given a quick once over looking for the obvious, but sometimes details are missed.

We have to remember that the purpose of a vaccine is to stimulate an immune response to a specific antigen.  If a horse is sick or not feeling well, then not only would it be possible that their immune system may not respond appropriately, but we may also actually do harm to that animal. It is generally not a good idea to vaccinate a sick animal for these reasons.  We are often better to wait, let them recover and then vaccinate when it is more appropriate.

Other reasons that a horse may not respond appropriately include concurrent diseases that may be impacting the immune response which may include things like insulin resistance and Cushing's disease.  Age also plays a role in the immune response and many older horses fail to respond appropriately for this very reason due to a failing or debilitated immune system for various reasons.

Now, one area of interest to me is those horses that tend to develop signs of laminitis within 2-3 days post vaccination.  We all see it as a veterinarian, but the reasoning as to why it happens has yet to be determined.  Personally, I tend to feel that these horses are more predisposed to metabolic syndrome, insulin resistance and even Cushing's disease, but have yet to be diagnosed.  In reality, most of these 'laminitic reactors' are the easy keepers of the group, more likely to be overweight and often have a history of laminitis.  So, what causes them to be pushed over the edge?  Again, in my opinion, it is linked to an ongoing inflammatory cascade that is occurring within that particular animal.  The vaccine can be seen as fuel added to a glowing ember, soon igniting it into a flame.  I often view those horses as ticking time bombs of inflammation, waiting for the right situation to get flared up.  Vaccines are the perfect medium to achieve this.

General Recommendations:

As a veterinarian and horse owner, I do believe in administering the core vaccines to every horse.  Does that mean that every horse in my practice gets those core vaccines?  The answer is 'NO'. Does that mean that I see more clinical sickness in those horses that have NOT been vaccinated?  The answer here is "NO" again.  I believe in vaccinating for those illnesses that have a high mortality rate, which includes tetanus, rabies and encephalitis.  Dependent on the situation and geographic location, these core diseases can be readily prevalent, very costly and difficult to treat and yet so easy to prevent. I also believe in risk based vaccines in the right situations, but not in all situations.

As any horse owner can testify, there are many cases of equine infectious diseases ranging from Influenza to Rhinopneumonitis in horses that have been vaccinated properly.  Here again, we have to raise the question as to why this occurs?  First, as stated, no vaccine is 100% effective in preventing disease.  The goal with any vaccine should be to reduce clinical morbidity.  Second, we have to take into consideration the amount of stress that some of these horses are under at the time of vaccination as well as during competition.  Stress in the competitive horse has been discussed in another article, but sometimes their stress levels can impact the immune function, making them more prone to various diseases.  Sometimes, I think it is better to keep these particular horses healthy with immune supportive herbs as well as adaptogens to help counter the stress, than it is to overwhelm them with vaccines.

If we have a horse that is turned out on pasture 24/7, they are often less prone to infectious disease development than those that are stalled constantly or in training/competition.  Again...we have to take into consideration the impact of stress.  I feel it is more important to address these horses through nutrition and herbal supplementation, keeping the immune system strong, trying to offset the impact of their current conditions.

I believe that we really need to evaluate each horse as an individual, taking into consideration all of the factors mentioned above.  The AAEP recommends this approach to us, as veterinarians, but all too often we fail to follow these guidelines due to time constraints and other factors.  If I have a horse on a farm that never leaves and is never exposed to other horses, I am going to vaccinate them differently than one that is competing at different locations once monthly.  The risk factors are different and taking into consideration that no vaccine is completely without harm, we want to minimize risk.

I also think we need to evaluate those horses that react negatively to vaccines more thoroughly.  If a horse has an allergic reaction to a vaccine, we need to question why.  Was it the brand of vaccine?  Was it the location where it was injected?  Was the horse sick at the time?  We need to figure out why and not just treat and move on to the next year.  We also need to investigate those horses that develop signs of lethargy or even laminitis, by looking a little deeper for underlying health concerns.  At the very least, we need to stagger vaccines by 2-3 weeks, instead of potentially overloading these particular horses with 4-5 antigens at one time.  Not only does this reduce the antigen load and immune challenge to the horse, but it may also allow us to pinpoint which vaccine is causing the reaction.

In the end, vaccines are a vital part of maintaining equine health.  This being said, they are not without harm and consideration needs to be given to make sure they are administered appropriately, at the right time and at the right intervals, taking into consideration the many risk factors involved.  Be an astute horse owner!  Take into consideration the many variables when deciding what your horse should be vaccinated against!

Dr. Tom Schell has over 18 years of equine medicine and surgery, as well as being head of research and development for Nouvelle Research, Inc.  Dr. Schell may be reached by email at [email protected]
Nouvelle Research, Inc. is the developer and manufacturer of the Cur-OST line of equine anti-inflammatory products, the only equine supplement using Curcumin as the primary ingredient to reduce inflammation, enhance health and performance for over 7 years.  Our goal at Nouvelle Research, Inc. is to enhance the health of our equine companions naturally and effectively, while also providing a source of information for the horse owner.  These and other articles may be seen on our website at: http://nouvelleresearch.com/index.php/articles
For more information about Nouvelle Research, Inc, please visit:  www.nouvelleresearch.com or call 1-800-476-4702

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