South Shore Equine Clinic & Diagnostic Center
Equine Veterinary Services South Shore Boston Massachusetts

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General Equine Care


Deworming and Gastrointestinal Parasite Control


Other Considerations


Horses evolved in the wild for thousands of years before they were domesticated by humans. In the wild, a horse typically spends as much as 18 hours per day (or more) eating vegetation (such as grass). Their digestive tract, therefore, has evolved to handle small quantities of easily digestible feed over a long period of time. Nowadays, the typical horse owner will give their horse a bolus of feed (such as hay or grain) in the morning before they go to work and a second bolus at night when they get home. Obviously, this increases the horse’s risk for the development of gastrointestinal problems. We recommend the following:

  • Feed small amounts of feed as frequently as possible. This is how horses are designed to eat.
  • Feed as much fresh grass as possible during the entire year. Grass is very easily digestible and acts as a natural laxative. Be careful about putting horses out on fresh spring pasture for an extended time.
  • Try to match the horse’s energy intake with his/her energy expenditure. Overweight horses are more prone to development of problems such as certain types of colic, laminitis, decreased performance, etc. An easy way to determine the horse’s normal weight is to use the ribs as a guideline:
    – Normal horses: the ribs are not visible but are easily palpable (felt with fingers).
    – Overweight horses: the ribs are not visible and are not palpable.
    – Underweight horses: the ribs are always visible.
  • Note that the level of protein intake is not necessarily proportional to the amount of energy intake. In fact, fat provides much more energy per gram than protein.
  • Use caution when feeding Bermuda Coastal Grass hay. This hay is very palatable and is an excellent source of nutrition. However, it has been associated with the development of distal ileal (small intestinal) impactions, which often warrant surgical correction (i.e. colic surgery). Therefore, we recommend physically mixing the hay with another hay (such as alfalfa, Timothy, Oat, etc.) at a proportion of Bermuda Grass less than or equal to 50%:other greater than or equal to 50%. This will drastically reduce the chance of developing ileal impactions.
  • Administer grain only to those horses that require increased energy intake (are unthrifty or are performing on a regular basis).
  • Administer electrolyte salts or a salt block on a daily basis. This will provide essential macro minerals, improve general hydration (which improves performance), and soften ingesta (which helps prevent colic).
  • Monitor the water temperature. Many horses won’t drink very cold water. Pregnant mares frequently require special consideration in regard to feeding during and after pregnancy. If you have any questions regarding a feeding program for a pregnant mare, please don’t hesitate to contact one of our staff.

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Internal parasites (worms) can cause extensive internal damage to your horse without you even realizing that your horses are infected.  There are over 150 species of worms that can infect horses.  The most important, in terms of health risk, are large and small strongyles, ascarids, and tapeworms. 

Where We Are Today And What is Best For Your Horse

New research has shown that deworming on a rotation every 6-8 weeks is not the best way to care for horses anymore.  Because of the emergence of anthelminthic resistance we are recommending a new system of fecal testing, deworming, and protecting the environment to rid horses of any existing infection; as well as preventing horses from becoming infected with parasites in the first place.

First and foremost, for optimal impact, you must give the right dewormer at the effective dosage at the appropriate time of year.  The idea of rotational deworming between different drug classes was based on the premise that some parasites will survive treatments with a particular dewormer. If you use the same drug class in successive treatments, the surviving parasites can reproduce with new generations resistant to that particular drug class. This is  the problem that some farms are experiencing and why the industry as a whole needs to make a concerted effort to deworm based on fecal egg counts and  by targeting the specific parasite(s) present.

Timing of deworming is very important. Consider the small strongyle larvae, for example. Small strongyle larvae are able to migrate and hide in the wall of the large intestine and are not affected by many of our common anthelminthics. These larvae begin to emerge as the days get longer (March-April). We often see an increase in fecal egg counts (FEC) at this time. By deworming for small strongyles at the proper time in your area of the country, we can thwart extensive egg laying that would contaminate spring pastures and perpetuate infection the rest of the year.  Many of our current dewormers kill only the adults. It is ideal to deworm with a product that will treat both the adults as well as the larvae twice annually.  It is also important to use a product that will kill tapeworms, as these parasites reside farther up the GI tract and do not always show up in routine fecal testing.

It is imperative to ensure you are giving the proper dosage to your horse, which is based on his/her body weight. Your horse’s bodyweight should be measured and recorded with a weight tape annually. The weight tape gives an estimation of your horse’s bodyweight by girth size.

Lastly, it is important to be sure that your horse gets and swallows all of the deworming medication. Ask for assistance if your horse resists oral administration.

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Determining The Effectiveness Of Your Deworming Program

Previously we reviewed the importance of identifying horses within your barn with high intestinal parasite loads and how to effectively deworm these horses. The next step is ensuring that the dewormer you used is effective – that it will kill off any parasites that you horse may have by at least 90-100%. With the emergence of dewormer resistance, this is a crucial step in management of parasite loads on your farm and the overall wellness of your horse(s). Unfortunately, it is often overlooked by horse owners.

To determine the effectiveness of the dewormer you are using, as well as your overall deworming program, it is essential to perform serial fecal egg counts (FECs). FEC testing determines the concentration of parasite eggs in manure. Initially, a FEC should be done to determine the parasite load of your horse. If your horse is    negative, then your deworming program is probably ok; however, another FEC should be done at the egg reoccurrence period (ERP). If your horse is positive, a second FEC should be performed 10 to 14 days after deworming to establish the effectiveness of the product used (you should expect a FEC near zero). If the FEC is still high, then your horse has resistance to that product. A dewormer from a different drug class should then be used and the FEC repeated in 10-14 days to establish its effectiveness.  

The final FEC should be done at the egg reappearance period (ERP). The ERP is a predictable interval where the FEC remains low after an effective deworming agent is administered and it differs slightly depending on the deworming product used. The normal ERP is 4-5 weeks for benzimidazole and pyrantel products, 6-8 weeks for ivermectin, and 12 weeks for moxidectin.  The second FEC helps to determine which horses have a high parasite load (encysted larvae) and/or if your farm or paddock has a parasite problem (re-infection). By identifying the “problem” you can provide targeted treatment of the individual horse and/or environment. 

Cleaning manure out of stalls daily and paddocks 2-3 times weekly is essential to controlling   parasite contamination of your horse’s environment. Rotating paddocks periodically in the hot, dry months allows larval stages to emerge and die off without finding hosts. If you spread your manure over actively grazed areas, it is best to compost it prior to spreading it, as the heat generated during the process kills the parasite eggs.  Additionally, you always want to deworm new horses and check their FEC prior to turning them out with the herd to minimize contamination by an unknown host.

Research has found that once a farm and its horses have been cleared of parasites, many horses only need to be dewormed twice yearly with an Ivermectin-Praziquantel combination product to eliminate tapeworms and keep bots under control.  This approach to strategic deworming and parasite control will minimize the potential of developing resistance and is better for the environment. It also stops us from giving unnecessary medications to our equine friends and, long term, minimizes costs to you, the horse owner.

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There is certainly no set rule for vaccination programs. Each horse is presented with a different set of circumstances and ongoing research with vaccines frequently results in new and different approaches. Currently, The South Shore Equine Clinic and Diagnostic Center recommends the following:

  • Administer a 3-way vaccine (which includes Eastern Encephalitis, Western Encephalitis, and Tetanus Toxoid) once a year, once every every 6 months if traveling to Florida..
  • Administer a 2-way vaccine (which includes Influenza and Rhinopneumonitis) a minimum of once every 6 months. If your horse is traveling or showing frequently, or is in a barn with horses that are traveling or showing frequently, we suggest vaccinating every 3-4 months (depending on the situation).
  • Administer Rabies vaccine once every 12 months.
  • Do not administer Tetanus Antitoxin to a normal horse. This is a therapeutic vaccine that should be administered to horses that have contracted tetanus. Tetanus Toxoid is a prophylactic vaccine that is administered every 6-12 months to normal horses.
  • Horses can sometimes feel "under the weather" for several days following administration of the Influenza/Rhinopneumonitis vaccine. The South Shore Equine Clinic and Diagnostic Center uses the safest and most effective brands of this vaccine in order to prevent the "post-vaccination blues". Most of our patients are now receiving this vaccine intranasally.
  • Strangles vaccination is recommended for all horses showing or exposed to showing horses.  This intranasal vaccine is effective against Strep. Equi, a very contagious respiratory disease.
  • Equine fetuses are sensitive to the standard Rhinopneumonitis vaccine. A different preparation of this vaccine,called Pneumobort K®, was developed for administration to pregnant mares. This vaccine should be administered at months 5, 7, and 9 of gestation.

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  • Oral Care:
    Since horses' teeth continually grow throughout their lifetime, they rely on dental occlusion to wear their teeth and prevent excessive tooth length. Each horse, of course, has different oral anatomy and therefore wears their teeth differently. Many horses will develop dental points, hooks, waves, etc. as a result of malocclusion. Horses with one or more teeth missing should receive special attention to the occluding teeth. We recommend comprehensive oral examination for each horse. The examination will reveal information that is needed to formulate an effective dental care program for each horse.

  • Sheath Cleaning (Geldings Only):
    Again, every horse is different. We recommend inspecting your horse’s sheath once every 4 weeks for a period of 6 months. The urethral orifice should always be checked for the presence of a "bean". Doing this will give you an idea of how much secretion your horse produces and about how often he will require cleaning. Some horses require sheath cleaning once a month; others require it once every 4 months. If we can provide any assistance (such as cleaning your horse’s sheath with you), please don’t hesitate to ask.

  • Foot Care:
    Most horses require trimming at least every 6-8 weeks. Not every horse requires shoes on all (or any) feet. Some horses require corrective trimming/shoeing to improve performance and/or maintain soundness. Ask your farrier to develop a foot care program for your horse. We would be more than happy to provide assistance in any way that we can.

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