Preventative Care

Weighing risks and benefits of intervention against the risks and benefits of doing nothing.

The science of preventative medicine involves weighing risks and benefits of intervention against the risks and benefits of doing nothing. What are the risks of exposure? If exposed, what are the realistic rates of infection? Once infected, what are the effects of the disease? On the other hand, is the vaccination truly safe and protective?

It has been said that we’ve only helped horses in two ways since domestication: by deworming and by floating their teeth. All the rest of what we do to maintain equine health is to compensate for the negative impacts of domestication, with or without confinement. For example, vaccination for infectious diseases would be less necessary if we didn’t crowd lots of individuals in small enclosures. Other problems could be prevented by switching to continuous feeding, instead of offering “meals” to our horses. Since horses evolved to graze 18-20 hours per day, meal-feeding is unnatural, and can even induce some types of colic. So preventative care comes from a central goal – how can we decrease overall risks?

But good medicine always requires a balance. In some cases, over-vaccination might increase a patient’s risks. Just as one example, some analysis of the 2011 Rhino outbreak in Ogden, UT suggested that horses who were more heavily vaccinated for Rhino seemed to be MORE likely to develop neurologic disease. Similarly, over-treatment for internal parasites only serves to bolster the worms’ natural defense mechanisms, increasing the risk of drug resistance. And improper use of antibiotics also fosters resistance. Yet without these powerful medications, many patients would suffer from the most mundane of ailments.

At Montana Equine, we will help you to weigh these factors, and put you in the best possible position to make critical decisions for your herd.



The American Association of Equine Practitioners (AAEP) has well-considered nationwide guidelines, but beyond these general nationwide recommendations, the team at Montana Equine will help you formulate the best program for your horse’s specific risks and needs.

Fortunately, equine vaccine technology has improved, even compared with just 10 years ago. Not only are the newest vaccines MUCH more thoroughly tested these days (by measuring degree of protection, as well as safety), new technologies are emerging to confer longer-lasting, more balanced protection. Still, there is no perfect vaccine (100% safe, 100% protective), and some of the most widely-used products are minimally protective and carry some actual health risks of their own. So, in choosing the best vaccination strategy for your horses, you have to balance the actual risk of infection (likelihood of exposure AND severity of the disease) with the potential benefit of vaccination (degree of protection conferred, risk of adverse effects). In addition to rare side-effects of vaccination, such as local swelling or allergic reactions, evidence exists that too-frequent vaccination is itself a possible risk factor. Research has suggested some risk of over-vaccination, and as a general strategy, we abide by the “less-is-more” approach, and will work with you to avoid mindless “over-vaccination”.

Overwhelmed yet? With our knowledge of emerging technologies and tried-and-true vaccines, as well as local and national disease epidemiology, our team at Montana Equine is exceptionally well-qualified to help you design a vaccine strategy that works for your particular circumstances.

Our veterinarians are always happy to help you weigh the potential pros and cons of vaccination in order to help you develop the strategy that makes the best sense for you.

For more information on vaccinations, please review Dr. W. David Wilson’s Vaccination Guidelines for Horses in the Western United States.



Strategic Vaccination Protocol:

Give Annual Vaccination, including West Nile Virus Vaccination

West Nile:

Montana has recently experienced very high state-wide incidence of horses diagnosed with West Nile Virus. The vaccines are highly effective with low rates of side effects. Fatality is greater than 1 in 3 for unvaccinated horses, and it can be a very ugly disease process.


We recommend Intra-Nasal Strangles vaccination (twice yearly) only when there is a current or recent outbreak on the premises. We may recommend giving this vaccine under certain circumstances, but due to sub-optimal protection and relatively high rates of side-effects, we do not consider this to be a CORE vaccine.

Pregnant Mares:

Vaccination with “killed Rhino” (we most often recommend “Pneumabort K”) is a critical means to minimize the risk of abortion due to Rhinopneumonitis (Herpes) Virus. This should be given at the beginning of the 5th, 7th, and 9th months of gestation.

Foal Shots:

Foals born to mares fully vaccinated at 10 months of gestation:

  • Begin vaccinating at 5 months of age
  • Plan for booster shot at 1 month post-vaccination

Foals born to mares who have not been vaccinated (other than Pneumabort):

  • Begin vaccinating at 4-6 weeks of age
  • Plan for booster shot at 1 month post-vaccination


Due to the increasing risk of Rabies infection in our region we recommend vaccination against this disease as part of the core vaccination strategy. The vaccine, given once-yearly, is also recommended as a core vaccine by the AAEP.

Please contact us with any questions or concerns regarding these general recommendations. Again, we believe that one size does not fit all, and are happy to help you develop the best vaccination strategy for your particular herd health situation.


Please contact us with any questions or concerns regarding these general recommendations. Again, we believe that one size does not fit all, and are happy to help you develop the best vaccination strategy for your particular herd health situation.




As a result of recent research, our deworming protocol has changed at Montana Equine. In the past, we have recommended deworming four times per year with specific de-wormers targeting specific parasites. We no longer recommend rotation of de-wormers in most circumstances.

In fact, recent research has shown that in a herd setting, 3% of horses will carry 90% of the worm burden. In addition, there is a growing concern that parasites are becoming resistant to commonly-used de-wormers. Although this resistance remains rare in Montana and similar climates, we are now recommending that all horses greater than one year of age be screened for parasites via a fecal float, instead of arbitrarily dewormed. This will help identify chronic carriers, ensure that we decrease parasite resistance, and thus maintain drugs that are efficacious against parasites for the future.

A fecal float is a cheap, non-invasive test that requires only a manure sample from your horse. This manure sample is mixed with water, spun in a centrifuge, and then strained. The manure pellet is mixed with a sugar solution, re-centrifuged, and allowed to float to the surface for easy detection. If parasite eggs are found in your horse’s manure, we can indentify the eggs and recommend the best de-wormer for your horse.

One thing to keep in mind is that tapeworm eggs and encysted strongyle eggs might avoid detection. As a result, we do recommend that you deworm your horse(s) at least once a year in the fall with an ivermectin/praziquantel product (such as Zimectrin Gold, or EquiMax).

We realize that there are herd situations where obtaining an individual sample from every horse might be challenging and that individual screening requires a larger amount of money up front. Please call us to discuss discounts on fecal testing for larger groups of horses.

In the long run, fecal floats can identify chronic carriers, reduce the de-worming treatment for the overall herd, and minimize the money spent on de-wormer. In addition, the horses that are not burdened by parasites will not receive medications that they don’t need. We are open to helping you develop effective alternative strategies for minimizing worm infestations in your horses. Please contact our herd health and internal medicine specialists to discuss your goals and to personalize the safest approach.

De-worming in Foals:

When considering deworming your foal, we would recommend beginning to deworm at 6-8 weeks of age.

Foals can be affected by large numbers of ascarids in their gastrointestinal tract. These large parasites can even cause impactions! You should de-worm beginning at 6-8 weeks of age, and repeat every 8 weeks. We typically recommend products containing fenbendazole or oxybendazole. Following this initial series of deworming, yearlings can begin a yearling/adult program of annual fecal floats.

Generally speaking, we do not recommend using the drug Moxidectin (the product “Quest”) on a regular basis. Although there are occasionally circumstances when we might recommend Quest, side effects have been reported, especially in younger horses.

The outline below reflects our general overall de-worming recommendations. Are your horses on drylot? Do they travel a lot? Are there many or few horses per acre? All these questions can contribute to helping design a de-worming program to suit your circumstances. As always, we recommend routine testing of your horses’ feces to monitor their current potential worm burden. Although some worms (encysted small strongyles and tapeworms, most notably) can escape detection, routine testing can help identify horses with heavier parasite burdens, allowing treatment and minimizing the risk to ALL the horses in the local environment