Why Spring Vaccines and Fecal Egg Counts Matter

By March 30, 2018 No Comments

Warmer weather is on the way, and it’s time to gear up for spring and summer riding season! As the bugs reappear and horses start traveling, now is the time for your horse’s annual spring vaccines and fecal.

At Premier Equine Veterinary Service, we generally recommend vaccinating for Eastern and Western Encephalitis, West Nile Virus, Tetanus, Influenza, and Rhinopneumonitis in the spring (all in one vaccine, Vetera Gold), with rabies vaccination in the fall. In addition, horses that are traveling or will be exposed to other horses may be vaccinated with the strangles and/or Potomac Horse Fever vaccine in the spring, and with an influenza/Rhinopneumonitis vaccine again in the fall.

And don’t forget, all horses should have a fecal egg count performed to determine parasite load and deworming routine. Want to know why horses need all of these? Read below for more information.


Certain vaccinations are recommended for all horses, while the decision of whether to vaccinate for other diseases may be based on numerous factors. Important considerations when deciding which vaccines to administer include:

  • The horse’s age and health status
  • Exposure to other horses and animals
  • Geographic location
  • Travel

The core vaccines, as described by the American Association of Equine Practitioners (AAEP), are those “that protect from diseases that are endemic to a region, those with potential public health significance, required by law, virulent/highly infectious, and/or those posing a risk of severe disease. Core vaccines have clearly demonstrated efficacy and safety, and thus exhibit a high enough level of patient benefit and low enough level of risk to justify their use in the majority of patients.” Core vaccines include the following:

  • Eastern and Western Encephalitis (EEE/WEE): EEE and WEE are transmitted by mosquitos to horses. Mosquitos pass the virus to horses from infected birds and rodents, which are the natural reservoirs of disease. Transmission from horse to horse or horse to human is unlikely; however, it is important to note that this disease can also affect humans. In horses, the virus causes neurologic signs and can be fatal. After an initial booster series of two vaccines 4 weeks apart, horses are generally vaccinated annually in the spring before onset of insect activity. In some areas with year-round mosquito populations, horses may be vaccinated more often.
  • West Nile Virus (WNV): WNV is spread to horses by mosquitos who have bitten infected birds. The virus causes encephalitis (inflammation in the brain), which manifests in signs such as ataxia (incoordination), head tremors, head pressing, circling, and further neurologic signs. The disease can be fatal, and approximately 40% of those that recover have residual signs after recovery. Like EEE/WEE, a booster series of two vaccines four weeks apart is given initially followed by annual vaccination.
  • Rabies: Although rare in horses, rabies is invariably fatal, and can be fatal to any exposed humans as well. Therefore, vaccination is recommended for all horses. Exposure occurs through bites from infected animals- usually wildlife, but any mammal is susceptible. Clinical signs may not appear until 2-6 weeks after infection and can be vague and non-specific initially but are rapidly fatal as the virus migrates to the brain. Annual vaccination is recommended.
  • Tetanus: Tetanus is caused by an anaerobic spore-forming bacteria, Clostridium tetanii, that is ubiquitous in the environment. Infection occurs through wounds, particularly deep puncture wounds. The horse may initially act colicy from the neurotoxin the bacteria produce, then develop muscle spasms, hypersensitivity, and difficulty opening the jaw (“lockjaw”). Eventually the horse will develop a stiff, sawhorse stance and finally become recumbent. Tetanus is fatal, often despite treatment. Horses should be vaccinated annually after the initial booster series. If it has been more than 6 months since vaccination and horse develops a wound, a booster vaccine may be recommended.

Other vaccines, often termed “risk-based” vaccines, may be given depending on a horse’s individual risk. These include influenza, rhinopneumonitis, strangles, Potomac Horse Fever, botulism, and others. Some of the ones most commonly recommended in this area include:

  • Influenza/Rhinopneumonitis: These vaccines are most often given together in a single injection. Both are upper respiratory diseases caused by a virus. The viruses are spread by nasal secretions, either directly through the air or via objects like brushes and clothing. Influenza/Rhinopenumonitis vaccines should be given to horses who are likely to contact a varying horse population, such as those who are competing, showing, or are frequently ridden or turned out with new horses. Many competitions require proof of vaccination. Boosters are recommended every 6 months after the initial series. Equine Herpes Virus 1 is also associated with abortion, so it is recommended that mares are vaccinated for EHV-1 (“Pneumabort-K”) at 5, 7, 9, and 10 months of pregnancy. EHV1 is associated with the reportable neurologic disease Equine Herpes Myeloencephalitis as well; however, the vaccine is not labelled as effective against the neurologic form of disease.
  • Strangles: “Strangles” is the common term for infection with Streptococcus equii equii which causes an upper respiratory infection with causes fever, lethargy, nasal discharge, and swelling +/- abscess development in the lymph nodes (most often those in the head and neck). The disease is very contagious, so affected horses and premises must be kept in quarantine during outbreaks. There are two main vaccines- a killed vaccine administered intramuscularly, and a modified-live vaccine given intra-nasally. The intra-nasal modified live vaccine offers greater protection, but killed is recommended for pregnant mares. Neither is completely effective in preventing disease but can reduce severity and incidence.
  • Potomac Horse Fever: PHF is caused by the bacteria Neorickettsia risticii, which is ingested with water bugs and causes fever and colitis. Laminitis can also occur due to the systemic inflammation the disease causes. The vaccine is not completely effective at preventing disease, but does seem to decrease severity of disease if horse’s become sick. Horses living in or travelling to endemic areas (eastern United States) should be vaccinated every 6-12 months, during active insect season.

There is a slight risk of adverse event any time a vaccine is given. The most common is mild local swelling or soreness and a transient fever and dull attitude. More serious side effects, including anaphylaxis, hives, colic, or purpura hemorrhagica (vasculitis and swelling), are luckily very rare. Vaccines in the “core” group are generally well-tested and safe with benefits far outweighing risk. However, as noted above, it is important to discuss the choice of vaccines with your veterinarian based on your horse’s individual history and health status.


Fecals are generally recommended at least twice yearly to assess parasite loads and determine the best deworming protocol for each horse. A fecal egg count involves examining a small sample of the horse’s feces under microscope for parasite eggs. The number counted is then used to estimate the horse’s parasite burden, based on “eggs per gram.” It is important to note that not all parasites will shed eggs constantly or have eggs that are apparent by microscope, so deworming is recommended for all horses twice per year even when counts are “zero.”

In the past, “rotational” deworming on a 2-month schedule was recommended. However, in the past 20 years research has shown that this is not only unnecessary for many horses, but also created a parasite population that is resistant to dewormers. For most horse populations, about 20% of the horses will carry 80% of the parasite burden- meaning that the other 80% of the horses have just 20% of the parasites! Therefore, the average horse will be considered a “low shedder,” which is < 200 eggs/gram. These horses should be dewormed just twice a year in the spring and fall. Horses that are moderate shedders (200-400 eggs per gram of feces) require deworming four times per year, while the small percentage of horses that are “high shedders (>400 eggs/gram) should be dewormed every 2-3 months.

Horses may change shedding status over time if environment, herd dynamics, or health status changes, so repeating fecal egg counts twice yearly is important to monitor for changes. Furthermore, a horse that has parasite eggs detected on fecal egg count should have a “fecal egg recount test” (FERCT) performed two weeks after deworming to assess the efficacy of the dewormer against that horse’s parasite load. This is important in detecting and preventing the development of resistant parasite populations.

For further information about vaccines and fecal egg counts, follow the links below or contact us at Premier Equine Veterinary Service at 888-860-0244.

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