It’s easy to go on autopilot when it comes to your horse’s vaccination schedule. Spring rolls around and you simply schedule the same vaccines he received last year. Or maybe your veterinarian offers a health plan that includes vaccinations in its regular spring-checkup package. Either approach usually works just fine. After all, good habits are the foundation of any effective health-care regimen.

Nonetheless, it’s wise to periodically take a step back to re-assess the variables in your horse’s vaccination program—his health, lifestyle, the products available—and adjust accordingly. Whether it’s giving a different set of vaccines or changing the timing of the actual injections, many components of a vaccination program can be adjusted for optimum results.

Here are the four primary factors to consider when reviewing your horse’s vaccination protocol to ensure that it’s still providing your horse the best possible protection.

Factor 1: Which vaccines to administer

Quick, which vaccines does your horse usually receive? If the first thing that popped into your head was a jumble of acronyms or shorthand descriptions like “three-way” or “five-way,” the first step in your refresher is to review your horse’s current vaccination protocol.

Chances are good your horse gets all the “core” vaccines—those that protect against eastern/western equine encephalomyelitis, tetanus, rabies and West Nile virus (WNV)—diseases that pose a threat to horses regardless of individual circumstances. But there’s a larger group of vaccines considered “risk-based,” meaning that they are recommended depending on a specific factors such as lifestyle, region and health.

Pull out your written records and take a look at the detail regarding the vaccines your horse has received over the previous few years. Terms like “three-way” and “five-way,” refer to the number of vaccines in a particular injection, with each encephalitic disease counting as a single “way” and sometimes being referred to collectively as “sleeping sickness.” Typically, three-way injections include vaccination against eastern and western equine encephalomyelitis and tetanus. Many four-way vaccines add in influenza—more recently some now offer West Nile virus protection—if it only says “four-way” in your records it can be hard to know. When influenza, rhinopneumonitis and West Nile virus are included, you may have a “six-way” vaccine. It’s important to note these products may not contain all the core vaccines and the specific type of vaccine included may vary among manufacturers. Whether your horse receives a “three-way,” “four-way” or “six-way,” you need to know which diseases are being prevented.

Factor 2: Life changes your horse experienced

The vaccine regimen that was sufficient to protect your horse a few years ago, or even last year, may no longer be suitable for him now. Changes in his lifestyle or surroundings can significantly increase or decrease his risk of contracting certain diseases. A review of the following factors will tell you whether your past vaccine plan is still appropriate or whether you need to add a vaccine to your horse’s protocol or if you can safely drop one:

• Location: Geography can have a significant impact a horse’s disease risk. For instance, horses in the southeastern United States will encounter more mosquitos than those in arid or chilly regions, so more frequent vaccinations against the mosquito-borne diseases may be needed. In addition, changes in the climate mean certain diseases are now being seen more often in areas where they never used to occur. Keep that in mind when considering your location.

• Lifestyle: A horse who spends his weekends traveling to shows and events is going to come into contact with many more horses with unknown vaccination histories than one who just hangs out at the barn with a stable herd. If your horse’s competition schedule is going to be busier this year than last, consider bolstering his vaccination program. Conversely, you may be able to scale back on his immunizations if he’ll be spending the season just relaxing at home.

• Companions: Even if they don’t travel themselves, horses can be exposed to pathogens carried home by those who do. If your barn has high turnover or a large percentage of horses who travel to shows and competitions, your horse may need a more extensive vaccination plan than if he lived in a stable herd of homebodies. Also consider your neighbors. Insects and air currents carrying pathogens don’t stop at property lines. If the horses at an adjacent property travel often, you may want vaccinate your herd as if they do, too.

Factor 3: Your horse’s health status and activity level

Vaccines work by stimulating a horse’s immune system, but that response can be affected by an individual’s overall health. If a horse is ill or has been sick in the previous week or two, it may be advisable to put off a vaccination for another few weeks to give his system time to recover.

On the other hand, there’s no need to put off vaccinations for horses who have chronic health conditions such as heaves or metabolic disease. That also goes for horses with pituitary pars intermedia dysfunction (PPID, commonly called Cushing’s), even though the condition can affect the immune system. Research may eventually find that horses with PPID need more frequent vaccination than is the norm, but the current recommendations call for simply keeping them on standard protocols.

Like health status, a horse’s stress level influences his immune system’s response to a vaccination. If your horse has been under stress or will be—perhaps you’ll be trailering him to a competition, for instance—it may make sense to hold off on administering his vaccinations until after he returns and is back to his regular routine.

Factor 4: Timing of vaccinations 

When a horse is immunized against a disease for the first time, he may need to receive an initial series of the vaccinations. For instance, the protocol may call for three doses four weeks apart. Each vaccine has its own protocol. No matter how it’s given, though, this initial series “teaches” the immune system to recognize the pathogen and mount a response. After the initial series is completed, vaccines are boosted annually or, more often, with single injections. These booster shots are effectively “reminders” to the immune system about that disease.

Because it can take days or weeks for a horse’s system to respond to a vaccine, the timing of injections and boosters can be critical. For instance, for maximum effect against insect-borne diseases, initial vaccine series and boosters need to be completed three to six weeks before the buggy season. If you’ve waiting until the weather warms up to think about spring vaccines, you’re already behind the ideal schedule. Of course, it’s better to vaccinate late than not at all. If late-season vaccination is unavoidable, do it anyway and resolve to plan better next spring.

Finally, there’s one other factor to keep in mind when planning your horse’s vaccination schedule: Some horses react to the adjuvant in the vaccine—substances added to boost the immune system’s response. These are not actually adverse reactions, which are potentially serious negative responses to a medication or treatment, but they can leave a horse feeling slightly rundown for a day or two. A horse can also develop soreness at an injection site for a day or two, making him uncomfortable or limit-ing his range of motion—two things you don’t want before an important event or competition.

Vaccination is one of the best ways to keep your horse healthy. By all means, make it a habit. But don’t just do it habitually. Periodic reviews of your horse’s lifestyle and risk factors will help ensure that you’re making the most of this powerful tool. 

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