Vaccination Guide for Horses: Schedule & List of Equine Vaccines

Staying up-to-date with required vaccines is important to keep your horse healthy and prevent the spread of infectious diseases.

Vaccines have been developed for 14 major equine diseases, including Strangles, West Nile Virus, Equine Influenza, and Equine Herpesvirus.

Some vaccines are recommended for all horses, while others are recommended based on your horse’s risk profile. If your horse lives in specific geographic areas, competes in performance disciplines, or frequently travels to events and shows, they may have a higher risk of contracting certain diseases.

Consult with your veterinarian to determine which vaccinations are recommended for your horse and to plan your annual vaccine schedule. As the saying goes, “An ounce of prevention is worth a pound of cure.”

Equine Vaccines

Vaccines are biological substances that stimulate the horse’s immune system to protect against diseases.

Vaccines can be made of either dead or weakened forms of viruses, bacteria, pathogenic organisms or other substances that cause disease in horses.

When administered to a horse, they trigger the body’s immune response to produce antibodies so the horse can recognize and fight the virus or bacteria if it is encountered in the future.

Antibodies are special proteins that attach themselves to foreign invaders in order to neutralize them. These antibodies remain in the horse’s system for weeks or months after vaccination, providing immunity against targeted diseases.

How Do Vaccines Work?

The immune system can be divided into two parts: the innate immune response and the adaptive response.

The innate immune system is the body’s immediate protective response to infection that attempts to kill the pathogen and prevent it from spreading.

The adaptive immune response is not active immediately when the horse is infected but rather develops in response to the specific pathogen affecting the horse.

Consequently, if the horse is reinfected with the same pathogen, the adaptive immune system mounts a stronger, faster response providing better protection or immunity against the pathogen.

Adaptive Immune System

The adaptive immune system responds in two ways: the cell-mediated response and the humoral response.

The cell-mediated response is carried out by T-lymphocytes (T-cells). T-cells work together with the innate immune system to recognize antigens, amplify the body’s immune response and destroy the pathogen.

The humoral response involves white blood cells known as B-cells (lymphocytes) and immunoglobulins (antibodies).

These immune cells detect structures on pathogens called antigens and respond by neutralizing the invading pathogen, so it is no longer harmful. B-cells also store a memory of the antigen so the horse’s body can fight back more efficiently against future infections.

Newborn foals develop immunity against diseases through the passive transfer of antibodies from their mother. When a mare has immunity to a specific disease, immunoglobulins (antibodies) are passed to her foal in colostrum, providing protection to the foal against the same disease.

How to Administer Vaccines

Vaccines must be administered by or under the supervision of a veterinarian. ^[3]

The location of injection is chosen to minimize adverse reactions to the vaccine and to maximize the safety of the horse and the person administering the vaccine. ^[3]

The ideal injection site is a large muscle that is used by the horse a lot, such as the base of the neck or the hamstring. ^[3]

Neck injections should be administered at the base in an area surrounded by the crest of the neck (nuchal ligament), the shoulder blade, and the cervical vertebrae, which run from the poll to the shoulder. The hamstring muscle can be injected at least one inch below the tuber ischii bone in the horse’s rear.  ^[3]

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Types of Vaccines

Vaccines initiate the body’s adaptive immune response, so the horse develops immunity against a pathogen without developing a clinical infection.

Several types of vaccines have been developed using different methods of stimulating an adaptive immune response. Types of vaccines include inactivated, modified live, recombinant, toxoid, subunit and DNA vaccines.

Inactivated Vaccine

Inactivated or killed vaccines are made by treating the targeted pathogen with heat or chemicals to inactivate or kill it. The pathogen can then be administered in the vaccine without harming the horse. ^[2]

Inactivated vaccines are made using an adjuvant which helps the vaccine elicit an immune response in the horse. ^[2] These vaccines are easy to store and are usually very safe because the pathogen is no longer effective. ^[2]

Immunity from inactivated vaccines develops slowly and often requires multiple doses and boosters. This type of vaccine causes a humoral response but is less effective at eliciting a cell-mediated immune response in the horse. ^[2]

Modified Live (Attenuated) Vaccine

Modified live vaccines (MLVs) are also called live attenuated vaccines because they are made with an attenuated or weakened pathogen. MLVs are made by mutating parts of the pathogen to elicit an immune response in the horse without causing harmful clinical signs. ^[2]

MLVs cause a stronger and longer-lasting cell-mediated and humoral immune response than inactivated vaccines. MLVs also require fewer doses and do not require an adjuvant. ^[2]

MLVs must be stored carefully according to the manufacturer’s instructions. MLVs also pose slightly more risk than inactivated vaccines, particularly for pregnant mares, who may abort after being vaccinated with an MLV. ^[2]

Recombinant Vaccine

Recombinant vaccines are made by inserting the genetic material from the targeted pathogen into a vector, such as a bacteria or yeast cell.

The vector uses the genetic material to produce the antigen of the pathogen being vaccinated against, stimulating an immune response from the horse. ^[2]

Toxoid vaccine

Toxoid vaccines are made using an inactivated toxin produced by the pathogen to stimulate an immune response in the horse.

Subunit vaccine

Subunit vaccines are very similar to inactivated vaccines but only contain the antigenic parts of the pathogen.

Subunit vaccines are very safe because they do not contain the virulent portion of the pathogen and are less likely to cause a reaction at the site of injection . ^[2]

DNA vaccine

DNA vaccines are produced by making the pathogen’s DNA into a plasmid, a circular piece of DNA. The plasmid is incorporated into the vaccine so that when administered to the horse, the antigen will be produced, stimulating an immune response. ^[2]

DNA vaccines are very safe because they do not contain the pathogen itself. ^[2]

Which Vaccines does my Horse Need?

Vaccines have been developed for 14 equine diseases and divided into core and risk-based vaccines. All horses should receive core vaccines, while horses only require other vaccines if they are or may be at risk.

Core Vaccines

All horses should be kept on a regular schedule to stay up to date on the core vaccines.

Core vaccines protect against diseases that are considered a serious threat to horse health, highly contagious, or a risk to public health. Some core vaccines are only administered in certain locations, and some are legally required for all horses. ^[1]

The following core vaccines are safe and effective for use in horses: ^[1]

• Eastern/Western Equine Encephalomyelitis
• West Nile Virus
• Rabies
• Tetanus

Risk-Based Vaccines

Your veterinarian will recommend administering risk-based vaccines depending on your horse’s risk level and disease severity.

Your horse’s risk level depends on factors such as age, sex, breed, health status, exposure to the disease and exposure to other horses or fomites (animals or objects that may carry infections). The risk assessment will also depend on whether a disease is currently endemic in the horse’s geographic region.

The following risk-based vaccines are frequently used in horses:

• Equine Influenza
• Equine Herpesvirus
• Potomac Horse Fever
• Strangles
• Anthrax
• Botulism
• Equine Viral Arteritis
• Leptospirosis
• Rotavirus
• Snake Bite

Ask your veterinarian which risk-based vaccines they recommend for your horse.

1) Eastern/Western Equine Encephalomyelitis (EEE/WEE)

EEE and WEE are rare notifiable diseases spread by mosquitos from birds to horses, humans, and other animals. There are several strains of EEE and WEE. ^[4]

Although most cases are subclinical with fever and malaise that resolves on its own. However, some cases progress to encephalitis and can be fatal.

Encephalitis refers to inflammation of brain tissues, resulting in central nervous system dysfunction. EEE and WEE cause similar symptoms in horses, including:

• Fever
• Headache
• Vomiting
• Appetite loss
• Lethargy
• Depression
• Diarrhea or constipation

Horses also experience neurological symptoms, such as involuntary muscle contractions, hypersensitivity, head-pressing or circling, inability to swallow, paralysis, recumbency, and convulsions. ^[4]

Some horses may be infected without showing any clinical signs of EEE or WEE. ^[4]

Equine Encephalomyelitis can be fatal, although EEE is more likely to result in fatality than WEE. Horses that recover often experience long-term neurological effects. ^[4]

Prevalence

Eastern and Western Equine Encephalomyelitis affect horses in North and South America. In the United States and Canada, EEE is mainly found in the eastern states and provinces, while WEE is mainly found in the western states and provinces. ^[4]

In North America, EEE and WEE are most prevalent in the summer and early fall when mosquito populations are the largest. These diseases are present throughout the year in the southern states, where mosquitos survive year-round. ^[6]

Vaccine

Inactivated vaccines are available for EEE and WEE, administered through intramuscular injection. There are also several multivalent vaccines for EEE and WEE, which protect against multiple varieties of a virus. ^[7]

Vaccination is effective if a regular schedule is maintained, however the immune response is highly variable between horses. Deaths caused by EEE/WEE have been reported in vaccinated horses. ^[7]

Antibodies to EEE and WEE can be passed to foals in their mare’s colostrum, establishing immunity through passive transfer. However, maternal antibodies can interfere with vaccines, preventing the foal from developing antibodies in response to the vaccine. ^[2]

For this reason, foals born to mares vaccinated prepartum likely will not benefit from being vaccinated before they are six months old. ^[2]

Recommended Schedule

Adult Horses over 1 year old:

• Previously vaccinated: Vaccinate once per year in the spring before vectors are prevalent. ^[8]
• Alternatively, vaccinate every six months if the horse is at higher risk of contracting EEE/WEE, is located in a region with a high prevalence of EEE/WEE, or was born to an unvaccinated mare. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate in two doses provided 4-6 weeks apart. ^[8]

Broodmares and Pregnant Mares:

• Previously vaccinated: Vaccinate with inactivated vaccine once per year, 4-6 weeks before the mare gives birth. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate in 2 doses 4 weeks apart. Vaccinate again 4-6 weeks before giving birth. ^[8]

Foals or Weanlings under 1 year old:

• Normal-Risk Foals: Vaccinate in three doses starting at 4 – 6 months old. Provide the second dose 4 – 6 weeks after the first dose and the third dose at 10 – 12 months old. ^[9]
• High-Risk Foals: Foals may be vaccinated at a younger age if they are at high risk of EEE/WEE. ^[9]
• Foals in the Southeastern US: An extra dose can also be given to foals at 2 – 3 months old because disease vectors are present earlier in the year. ^[9]

Side Effects

The following side effects may occur with any vaccine administered through intramuscular injection: ^[3]

• Local reaction at the injection site including pain and swelling
• Low-grade fever
• Anorexia
• Lethargy
• Stiffness in the muscle that was injected

Vaccines can also cause the following signs of an allergic reaction: ^[3]

• Hives
• Colic
• Diarrhea
• Purpura hemorrhagica (an excessive immune response that damages blood vessels, resulting in edema in the legs, belly, and lower chest, bleeding of gums and other mucus membranes, and pain)
• Anaphylaxis

Immune-compromised or ill horses may have a higher risk of side effects. If you have an immune-compromised horse, contact your veterinarian to determine whether the risks are worth the benefits of vaccination for your horse.

2) West Nile Virus (WNV)

West Nile virus is an RNA virus of the Flavivirus genus that can infect horses, humans, and other mammals. West Nile is also a notifiable disease. ^[5][10]

Birds are a natural reservoir for WNV. Mosquitos transmit WNV from birds to other mammals; this virus is not typically transmitted from horse to horse. ^[11]

Signs of West Nile virus in horses include:

• Fever
• Recumbency
• Fatigue

Horses may also experience neurological symptoms such as ataxia or incoordination, weakness, lameness or paralysis, muscle tremors, teeth grinding, and blindness.

Not all infected horses show clinical signs of WNV. However, this virus can be deadly, especially for horses that have developed neurological symptoms. ^[10][11]

West Nile in horses can appear very similar to other diseases, such as EEE/WEE or rabies, so care should be taken when diagnosing to avoid confusing it with other diseases.

Prevalance

Horses are at the greatest risk of catching WNV at times when mosquitos are abundant, which varies with temperature and precipitation. ^[10]

Vaccine

Inactivated and recombinant vaccines are available for West Nile virus, as well as several multivalent vaccines. ^[7] The vaccine is administered through intramuscular injection.

The West Nile vaccine can prevent or reduce the severity of infection and reduce viral shedding. However, it is not always fully protective against WNV. ^[2][14]

Some studies show that multivalent WNV vaccines are less effective than monovalent vaccines. ^[12]

One study found that foals can gain antibodies against WNV through passive transfer from colostrum. These antibodies decrease the efficacy of vaccines, making it unnecessary to vaccinate foals born to vaccinated mares before 6 – 7 months old. ^[13]

Vaccination Schedule

Adult Horses over 1 year old:

• Normal-Risk Horses: Vaccinate once per year in the spring before vector season. Initial vaccination with a killed vaccine may require more than one dose. See vaccine directions for details. ^[7][8]
• High-Risk Horses: Horses in high-risk areas may be vaccinated every six months. ^[7]

Broodmares and Pregnant Mares:

• Previously vaccinated: Vaccinate once per year, 4-6 weeks before giving birth. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate mares when open rather than during pregnancy. ^[8]

Foals or Weanlings under 1 year old:

• Normal-Risk Foals: Vaccinate in three doses giving the first dose at 4 – 6 months old, the second 4 – 6 weeks later, and the third at 10 – 12 months old. ^[9]
• High-Risk Foals: This strategy can be altered to vaccinate foals under 4 months if they are at high risk of WNV. ^[9]
• Foals in the Southeastern US: An extra dose can also be given to foals 2-3 months old because disease vectors occur earlier in the year. ^[9]

Side Effects

The following side effects can be caused by any vaccine administered through intramuscular injection: ^[3]

• Pain, swelling and stiffness at injection site
• Low-grade fever
• Loss of appetite
• Lethargy

Vaccines can also cause allergic reactions, including hives, colic, diarrhea, purpura hemorrhagica and anaphylaxis. ^[3]

Immune-compromised or ill horses have a higher risk of adverse reactions. Consult with your veterinarian to determine whether the WNV vaccine is safe for your horse.

While some West Nile virus vaccines are safe for pregnant mares, other vaccines can cause abortion or deformities in the foal. ^[15][16]

3) Rabies

Rabies is a reportable neurological disease that is usually deadly and can be transmitted to humans. It is caused by a virus that spreads to the central nervous system, causing brain and spinal cord inflammation.

This virus can present in a more common furious form or in a paralytic form. The furious form causes horses to show agitation and aggressive behaviour, while the paralytic form causes paralysis, particularly in the throat and jaw. ^[17]

Infected horses show various symptoms, including: ^[17]

• Fever
• Appetite loss
• Excess salivation
• Aggressive behaviour
• Clumsy movement/incoordination
• Pica (eating non-food items)
• Frequent whinnying
• Lethargy
• Self-harm
• Muscle tremors
• Paralysis
• Hypersensitivity

Rabies symptoms typically last between 12 hours and one week. As the condition progresses, the horse’s airways become paralyzed, ultimately leading to death. ^[17]

Horses can survive if treated immediately, prior to the onset of symptoms. Once symptoms appear, there is no treatment for rabies and no possibility of survival. ^[17]

Horses suspected of having rabies should immediately be vaccinated and isolated for 90 days. The horse should receive a booster shot three weeks and eight weeks after the first vaccine. ^[17]

Transmission

The rabies virus is found in saliva and other bodily fluids of infected animals. Horses become infected with rabies when they are bitten by an infected animal. ^[17]

Vaccine

The rabies vaccine for horses is an inactivated vaccine that is administered through intramuscular injection. There is also a multivalent vaccine, which includes vaccines for several other diseases. ^[7]

Rabies has been reported in young, vaccinated horses. This suggests possible interference from maternal antibodies although this has not been directly studied in horses. ^[7]

Because of this, vaccination of foals born to vaccinated mares is not advised until the foals are six months old. Your veterinarian may take a titre of the foal’s blood to determine whether a foal has sufficient antibodies or requires vaccination. ^[7]

Vaccination Schedule

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate once per year. ^[8]
• Never vaccinated: Horses over 20 years old that have never been vaccinated may benefit from two initial doses four weeks apart. ^[7]

Broodmares and Pregnant Mares

• Vaccinate once per year 4 – 6 weeks before giving birth. Alternatively, this vaccine provides extended immunity so it can be given before the horse is bred rather than during gestation. ^[8]

Foals or Weanlings under 1 year old

• Born to mares vaccinated in the prepartum period: Provide two doses of the vaccine, giving the first dose at 4 – 6 months old and the second dose 4 – 6 weeks after. See manufacturing directions for details. ^[9]
• Born to mares not vaccinated in the prepartum period: Vaccinate foals once at 4-6 months old. ^[9]

Two doses are recommended for foals whose mothers were vaccinated prior to parturition because the mare’s antibodies may interfere with the foal’s antibody response to the vaccine, preventing the foal from developing immunity. ^[9]

Side Effects

Potential side effects of the rabies vaccine are the same as those for other vaccines administered via intramuscular injection: ^[3]

• Local reaction at injection site
• Low-grade fever
• Loss of appetite
• Fatigues and weakness
• Muscle stiffness
• Allergic reaction

Monitor your horse for adverse reactions after receiving the rabies vaccination. If you have an immune-compromised horse, ask your veterinarian whether the rabies vaccine is appropriate.

4) Tetanus

Tetanus is a neurological disease caused by Clostridium tetani, a bacteria found in soil and in feces. ^[2]

C. tetani enter the horse’s body through open wounds or ulcers in the gastrointestinal tract, producing a neurotoxin called tetanospasmin. This toxin interferes with central nervous system signalling, resulting in uncontrolled muscle contraction. ^[18]

Horses infected with tetanus show clinical signs including: ^[18]

• Locked jaw
• Stiff limbs and neck
• Muscle spasms
• Rigid movement
• Difficulty with prehension, chewing and swallowing
• Muscle spasticity (heightened muscle tone, interfering with movement and daily functions)

Other signs of tetanus in horses include heightened sensitivity, holding the tail high, prolapsed third eyelid, and elevated heart rate. In severe cases, horses may also show recumbency, shortness of breath and a saw-horse stance in which their body is shifted over the back legs while the front legs are stretched out ahead. ^[18]

Prognosis

Death occurs in 24% – 80% of tetanus cases. Vaccination status influences the horse’s prognosis. ^[18]

Tetanus is treated with antibiotics, tetanus antitoxin, and supportive care. Horses diagnosed with tetanus or suspected of having tetanus should be vaccinated. ^[19]

Infected horses do not need to be quarantined because tetanus is not transmitted between horses.

Vaccine

Tetanus toxoid vaccines are available, as well as multivalent vaccines which include the tetanus toxoid and vaccines for several other diseases. The vaccine is administered through intramuscular injection. ^[7]

In addition to regularly scheduled tetanus vaccinations, horses that have open wounds should be vaccinated for tetanus. ^[7]

Foals can receive tetanus antibodies from their dam through colostrum. Foals born to mares vaccinated less than two months before birth may not benefit from tetanus vaccination before six months of age because of maternal antibody interference. ^[7][20]

Horses should receive annual boosters for the tetanus vaccine, although many horses maintain sufficient antibodies for several years. ^[7]

Vaccination Schedule

In addition to the following recommended schedule, horses should be vaccinated for tetanus if they sustain an injury or will undergo planned surgery, and their previous vaccine was over six months ago. ^[8]

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate once per year. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate with two doses provided 4 – 6 weeks apart. ^[8]

Broodmares and Pregnant mares

• Previously vaccinated: Vaccinate once per year, 4 – 6 weeks before giving birth. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate with two doses given 4 – 6 weeks apart. Provide an additional vaccine 4 – 6 weeks before the mare gives birth. ^[8]

Foals or weanlings under 1 year old

• Born to mares vaccinated in the prepartum period: Three doses are required; the first should be given at 4 – 6 months of age, the second 4 – 6 weeks after the first, and the third at 10 – 12 months old. ^[9]
• Born to mares not vaccinated or with unknown vaccination history: Three doses are required; the first at 3 – 4 months of age, the second 4 – 6 weeks after the first, and the third at 10 – 12 months old. ^[9]

5) Equine Influenza

Equine influenza virus (EIV) is a highly contagious respiratory disease in horses. EIV causes symptoms such as fever, lethargy, sore throat, coughing and nasal discharge.

The virus is transmitted when infected horses cough, expelling viral particles into the air. Horses can also contract influenza by coming into contact with objects that have been coughed on by infected horses, such as equipment, feed buckets, or clothing. ^[23]

EIV is quickly transmitted at shows and races, which can result in outbreaks. During an outbreak, competitions and horse transport are halted, and quarantine areas are established to stop the virus from spreading. ^[21]

The only treatment for influenza is to rest until the horse is recovered. EIV infections can also lead to secondary infections, which put horses at risk of complications.

Influenza is usually not fatal, although EIV infections in donkeys and mules tend to be more severe. ^[22]

Vaccine

The vaccine for equine influenza virus is an optional or risk-based vaccine that is administered to horses at high risk of infection or serious illness.

A modified live vaccine is available and administered intranasally. There is also an inactivated vaccine administered through intramuscular injection. ^[2]

The vaccine will not prevent all cases of Equine Influenza Virus. However, horses still benefit from reduced symptoms and faster recovery.

Antigenic Drift

EIV is challenging to vaccinate against because of antigenic drift – continuous genetic variation in the virus due to DNA mutation.

Vaccines are tailored to protect against the particular strain of virus currently endemic in horse populations. If a horse is vaccinated but becomes infected with another strain of EIV, it can still develop the disease.

To maintain the efficacy of the EIV vaccine, a panel of experts meets annually to determine which influenza strains should be included in the vaccine. ^[2]

Vaccination Schedule

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate once per year or every six months if horses are at continual risk of exposure to EIV. ^[8]
• Never vaccinated: Inactivated vaccines are provided in 2 – 3 doses, each given 3 – 4 weeks apart (as per the manufacturer’s instructions). Modified live vaccines are given once annually and are administered intranasally. ^[7][8]

Broodmares and Pregnant mares

• Previously vaccinated: Vaccinate with an inactivated vaccine once per year and 4 – 6 weeks before giving birth. ^[8]
• Never vaccinated or unknown vaccination history: An inactivated vaccine is provided in 2 -3 doses, each given 3 – 4 weeks apart (see manufacturer’s instructions for details). The vaccinations should be timed, so the last vaccine is administered 4 – 6 weeks before giving birth. ^[8]

Foals or weanlings under 1 year old

• Foals born to recently vaccinated mares receive influenza antibodies in colostrum, which can interfere with the effects of vaccination. These foals receive better protection if vaccinated at six months old. ^[24]
• An inactivated vaccine or modified live vaccine can be provided. ^[9]
• Inactivated vaccines are given at 4 – 6 months old in 2 – 3 doses, each given 3 – 4 weeks apart (see manufacturer’s instructions for details). ^[9]
• Modified live vaccines are given intranasally in one dose at 11 months old. ^[9]

Side Effects

One case report describes a broodmare that had seizures and gave birth prematurely to a healthy foal following vaccination for equine influenza, equine herpesvirus, and Rhodococcus equi.

This is the only case report of seizures in a horse that appears to be caused by vaccination. ^[25]

6) Equine Herpesvirus (EHV)

EHV, also known as rhinopneumonitis, is a contagious disease that affects the horse’s upper respiratory tract. It can result in respiratory or neurological symptoms, abortion, or a combination thereof. ^[26]

In many cases, equine herpesvirus infection is latently established in the horse for the rest of its life. Latent infections are activated by stress and cause the horse to be symptomatic and contagious. ^[28]

Several forms of equine herpesvirus exist. EHV-1 and EHV-4 have the greatest impact on horse health and welfare. EHV-1 and EHV-4 outbreaks are expensive because of treatment and quarantine costs and the cancellation of equine events. ^[28]

EHV can be fatal, especially in horses showing severe neurological symptoms such as multi-limb paralysis and urinary incontinence. In cases where horses do not fully recover, euthanasia is often recommended. ^[27]

There is no cure for EHV-1 or EHV-4. However, some measures help to treat clinical signs and reduce viral shedding.

Transmission

EHV is transmitted in nasal secretions and infected fetal or placental tissues. ^[27]

Vaccine

Modified live and inactivated vaccines against EHV have been licensed for use in North America and Europe. Only inactivated vaccines should be used in pregnant mares to prevent abortion. ^[2]

The equine herpesvirus vaccine is administered through intramuscular injection.

Vaccination against EHV does not prevent herpesvirus infection in horses, but does reduce clinical signs and viral shedding, making the horse less contagious. The vaccine also does not prevent sporadic EHV-induced abortions but has greatly reduced abortion storms caused by EHV. ^[2][26]

Antibodies against EHV are not completely effective in preventing infection because the virus can avoid being detected by the horse’s immune system. ^[27]

EHV antibodies are passed from vaccinated mares to their foals in colostrum. Maternal antibody interference prevents foals from developing antibodies in response to vaccination. Foals born to mares vaccinated prepartum should not be vaccinated before they are 5 months old. ^[2]

Vaccination Schedule

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate once per year, or every six months in horses under five years old, horses in contact with pregnant mares, or racehorses and show horses at high risk of contracting EHV. ^[8]
• Never vaccinated: Provide an inactivated vaccine in 2 – 3 doses 3 – 4 weeks apart, depending on the manufacturer’s instructions. ^[8]

Broodmares and Pregnant mares

• Regardless of vaccination status: Vaccinate at five, seven, and nine months of gestation with a vaccine specific to preventing EHV abortion. ^[8]
• Additionally, provide a booster vaccine that protects against respiratory disease 4 – 6 weeks before the mare gives birth. ^[8]

Foals or weanlings under 1 year old

• Vaccinate with modified live or inactivated vaccine at 4 – 6 months old, followed by a second dose 4 – 6 weeks later, and a third dose at 10 – 12 months old. ^[9]

7) Potomac Horse Fever (PHF)

Potomac Horse Fever (PHF) is a bacterial disease that causes fever, depression, appetite loss, lethargy, and diarrhea in horses, as well as abortion in pregnant mares. PHF may also result in dehydration, laminitis, or colic, which reduce the horse’s chance of recovery. ^[29][30]

PHF is usually treated with antibiotics, such as oxytetracycline, and IV fluids to keep the horse hydrated. ^[32] Death occurs in 5 – 30% of PHF cases. ^[29][31]

Transmission

Horses can become infected with PHF near rivers or streams where the bacteria Neorickettsia risticii is found. N. risticii live on aquatic insects and snails and can infect horses when ingested.

Aquatic insects that act as hosts for N. risticii include caddisflies, mayflies, damselflies, dragonflies and stoneflies. ^[33]

Prevalence

Potomac Horse Fever is seasonal, occurring mainly from late spring to early autumn, with most cases in July and August. ^[31][32]

Vaccine

The PHF vaccine is a killed vaccine that is also available in a multivalent format, although the multivalent vaccine is less effective. ^[30] The vaccine is administered through intramuscular injection. ^[34]

The vaccine prevents and reduces the severity of Potomac Horse Fever. However, there have been cases where vaccination failed to prevent PHF and associated abortions. ^[35]

The PHF vaccine can be ineffective in horses infected with a different strain of PHF than the strain they were vaccinated against. The vaccine can also be ineffective because in some cases it does not induce enough antibodies to protect against infection. ^[35]

While the PHF vaccine may be administered to foals as young as three months, vaccination is recommended when the foal is five months old. ^[34]

Foals born to vaccinated mares can receive PHF antibodies through passive transfer in colostrum. These antibodies would interfere with vaccination by preventing the foal from developing antibodies in response to the vaccine.

Vaccination Schedule

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate every 6 – 12 months, or every 3 – 4 months in areas where PHF is endemic. ^[8] Vaccinations should be timed to precede the season when PHF is most prevalent.
• Never vaccinated: Vaccinate with 2 doses provided 3 – 4 weeks apart. ^[8] Time vaccinations to precede the seasonal period when PHF cases peak. ^[34]

Broodmares and Pregnant mares

• Previously vaccinated: Vaccinate every six months. Schedule vaccinations so that one is administered 4 – 6 weeks before the mare gives birth. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate with two doses. The first should be given 7 – 9 weeks before the mare is due to give birth and the second at 4 – 6 weeks before the due date. ^[8]

Foals or Weanlings under 1 year old

• Normal-Risk Foals: Vaccinate with two doses. The first dose is administered at five months, and the second is administered 3 – 4 weeks later. ^[9]
• High-Risk Foals: In areas with a high risk for Potomac Horse Fever, foals can be vaccinated earlier than 5 months of age. Foals should receive a dose of the vaccine every four weeks until they reach six months old. ^[9]

8) Strangles

Strangles is a highly infectious disease that affects the horse’s upper respiratory tract and is fatal in up to 9% of cases. ^[36]

Strangles is caused by Streptococcus equi, a bacteria that is transmitted in nasal or ocular secretions of infected horses.

Strangles causes the lymph nodes to develop abscesses, which rupture after several weeks. Contents of the abscesses may drain into the guttural pouch and are released through coughing and nasal discharge. ^[36]

Inflammation of the horse’s pharynx (throat) and lymph nodes can obstruct the horse’s airways, making it difficult to breathe. Abscesses on lymph nodes near the eyes may cause the eyelid to swell. Abscesses can also occur in other areas, such as the brain, abdomen, or mammary glands. ^[36]

Signs of strangles include: ^[36]

• Fever
• Lethargy
• Reduced eating and drinking
• Nasal discharge
• Coughing
• Difficulty breathing
• Holding head in abnormal positions
• Eye discharge
• Swollen lymph nodes which may cause the skin to break and ooze discharge

Treatment

Horses can remain infected with strangles for several weeks or months and may face further complications, such as pneumonia. ^[36]

The primary treatment is rest. Anti-inflammatories and supportive therapy, such as intravenous fluids and tracheostomy, may also be beneficial.

Antibiotics are sometimes administered, however there is no evidence that antibiotics are an effective treatment for strangles. ^[36]

The best prevention for strangles in horses is good biosecurity protocols at equine facilities.

Vaccine

Two Strangles vaccines are available: a live attenuated vaccine administered intranasally and an inactivated antigen extract vaccine administered intramuscularly. Multivalent vaccines are also available. ^[36]

The inactivated antigen extract vaccine is not very effective; one study found it reduced clinical strangles infections by only 50%. ^[37]

The oral live attenuated vaccine should be administered with care and separately from other vaccines, injections, or procedures to avoid contaminating injection sites or open wounds with the live bacteria. ^[36]

The live attenuated vaccine also poses more risk to foals and is not recommended for horses under one year old. ^[36] Foals can receive antibodies against strangles through passive transfer in colostrum, which can interfere with the effects of vaccination. ^[36]

Horses should not be vaccinated with the live attenuated vaccine if they show any signs of strangles, had strangles in the last year, or have contact with horses that are or may be infected with strangles. ^[36]

Vaccination Schedule

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate every 6 – 12 months with a killed vaccine containing M-protein or a modified live vaccine. The killed vaccine should be administered every six months. ^[8]
• Never vaccinated or unknown vaccination history: A killed vaccine containing M-protein or a modified live vaccine can be administered. ^[8]
• The killed vaccine is given in 2 – 3 doses, each 2 – 4 weeks apart. See the manufacturer’s instructions for details. Horses vaccinated with the killed vaccine should be revaccinated every six months. ^[8]
• The modified live vaccine is administered in two doses. The second dose should be given three weeks after the first. ^[8]

Broodmares and Pregnant mares

• Previously vaccinated: Only the killed vaccine containing M-protein should be administered to broodmares or pregnant mares. The vaccine should be given every six months and timed, so it is administered 4 – 6 weeks before the mare is due to give birth. ^[8]
• Never vaccinated: Unvaccinated mares should be given three doses of the killed vaccine containing M-protein. The second dose should be given 2 – 4 weeks after the first dose, and the third dose should be given 4 – 6 weeks before the mare is due to give birth. ^[8]

Foals or Weanlings under 1 year old

• Normal-Risk Foals: Foals can be given the killed vaccine or modified live vaccine. ^[9]
• The killed vaccine is given in three doses with the first dose administered at 4 – 6 months old, the second dose 4 – 6 weeks later, and the third dose a 4 – 6 weeks later after the second. ^[9]
• The modified live vaccine is also given in three doses but is administered intranasally. The first dose should be given when the foal is 6 – 9 months old, the second 3 – 4 weeks after, and the third dose at 11 – 12 months of age. ^[9]
• High-Risk Foals: The modified live vaccine can be administered when foals are six weeks or older. When the vaccine is administered to younger foals, a third dose should be given 2 – 4 weeks before the foal is weaned. ^[9]

Side Effects

The strangles antigen extract vaccine can cause abscesses at the injection site and may cause purpura hemorrhagica on occasion. ^[36]

The oral live attenuated vaccine may cause lymph node abscesses, vasculitis (inflamed blood vessels), purpura hemorrhagic, and nasal discharge. There is a small risk of contracting clinical strangles. ^{[36][38][39][40]}

Live bacteria from the attenuated vaccine can cause abscesses in open wounds. To avoid contaminating wounds or injection sites, the oral vaccine should be administered at a separate time from other vaccines, injections, dental work, or medical procedures such as castrations. ^[36]

Foals under 1 year old are at the greatest risk of the side effects associated with the live attenuated vaccine. ^[39]

9) Anthrax

Anthrax is a reportable disease that can be transmitted from horses to humans. ^[41] It is caused by the gram-positive bacteria Bacillus anthracis, which is found in soil.

Horses become infected with anthrax when B. anthracis spores are inhaled, ingested, or enter the body through an open wound. ^[41] The spores produce a toxin that causes edema and cell death, resulting in damaged tissue and sepsis.

Infected horses should immediately be quarantined and treated. If not treated quickly, death ensues 2 – 4 days after the onset of clinical signs. ^[41]

Common signs of anthrax include:

• Fever
• Depression
• Colic
• Cyanosis (bluish skin caused by oxygen deprivation)
• Rapid or laboured breathing
• Rapid heart rate
• Muscle tremors
• Diarrhea containing blood
• Edema below the skin
• Bleeding from bodily openings, such as the mouth and nose ^[41]

Horses infected via oral ingestion of anthrax-contaminated feed also develop inflammation, ulcers, and bleeding in the small intestine. ^[41]

Treatment

B. anthracis is very susceptible to antibiotics such as penicillin and streptomycin. If caught early, the combination of these medicines can allow horses to fully recover from anthrax. ^[41]

Vaccines are protective against anthrax and are important preventative measures, along with good biosecurity. ^[41]

Vaccine

A modified live anthrax vaccine is available for horses and administered intramuscularly. The vaccine should not be administered at the same time as antibiotics because antibiotics can interfere with the horse’s response to the vaccine. ^[8][42]

If you are exposed to the equine anthrax vaccine through accidental injection, ingestion, broken skin, or an open wound, contact your doctor immediately. ^[42]

The anthrax vaccine should not be administered to pregnant mares. ^[42]

Vaccination Schedule

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate once annually. ^[8] Vaccination 4 weeks prior to turnout may be recommended in endemic areas ^[42]
• Never vaccinated or unknown vaccination history: Vaccinate with two doses given 3 – 4 weeks apart. ^[8]

Broodmares and Pregnant Mares

• Mares should not be vaccinated for anthrax while pregnant. ^[8]

Foals or Weanlings under 1 year old

• Vaccinated with two doses given subcutaneously 2 – 3 weeks apart. See the manufacturer’s directions for details. ^[9]

Side Effects

Vasculitis (inflamed blood vessels) and stiffness have been reported in horses vaccinated for anthrax. ^[41][43]

Serious adverse reactions have been reported in foals and miniature horses. ^[42]

10) Botulism

Botulism, is a neuroparalytic disease affecting both humans and animals. In foals, it is refered to as shaker foal syndrome.

Botulism is caused by the bacteria Clostridium botulinum, which produces an extremely dangerous neurotoxin. The toxin blocks neuromuscular signals leading to muscle weakness and potentially full-body paralysis. ^[41]

Other symptoms of botulism include: ^[41]

• General muscle weakness
• Slow eating
• Difficulty chewing and swallowing
• Drooling
• Drooping eyelid
• Dilated pupils
• Muscle tremors
• Weakened tongue and tail
• Stumbling
• Constipation
• Frequent urination
• Laboured breathing
• Fast heart rate
• Recumbency

Transmission

Horses become infected through ingestion, inhalation, or contamination of open wounds by C. botulinum or the botulinum neurotoxin.

C. botulinum is found in soil and decaying carcasses. This bacteria can contaminate forage, especially mouldy hay, or silage/haylage that as poorly fermented.

Treatment

Botulism can be treated with an antitoxin and supportive care such as mechanical ventilation is also beneficial. Early treatment is often successful. ^[41]

Prognosis

The prognosis for botulism varies depending on how much toxin the horse is exposed to and the specific serotype of botulinum toxin. Once the horse can no longer stand, the prognosis is poor. ^[41]

Botulism can be fatal if respiratory muscles are paralyzed. ^[41]

Vaccine

An inactivated toxoid vaccine for botulism is available, administered through intramuscular injection. A recombinant subunit vaccine has also been developed but is not yet commercially available. ^[41][44]

There are three serotypes of botulism in horses. Vaccines only protect against one serotype and are not cross-protective against other serotypes. ^[45]

In horses that have previously been infected with botulism, vaccination should commence once the horse’s antibodies have been depleted. ^[8]

Foals receive antibodies by drinking colostrum from vaccinated mares. Maternal antibodies do not appear to interfere with the efficacy of vaccination in young foals. Foals can be vaccinated as young as two weeks regardless of the mare’s vaccination status. ^[45]

Vaccination Schedule

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate once per year. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate with three doses administered 4 weeks apart. ^[8]

Broodmares and Pregnant Mares

• Previously vaccinated: Vaccinate once per year at 4 – 6 weeks before the mare gives birth. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate with three doses. The first should be administered at eight months of gestation, followed by a second four weeks after and a third another 4 weeks later. ^[8]

Foals or Weanlings under 1 year old

• Foals born to mares vaccinated during gestation: Foals should receive three doses of the botulism vaccine. The first dose should be administered when the foal is 2 – 3 months, followed by a second dose four weeks later and a third dose four weeks after that. ^[9]
• High-Risk Foals: In foals at high risk of botulism, the first dose can be administered at two weeks or older. ^[9]
• Foals born to unvaccinated mares or with unknown vaccination history: Foals should receive three doses of the vaccine. The first dose should be administered when the foal is 1 – 3 months old, followed by a second dose four weeks later and a third dose four weeks after that. ^[9]

Side Effects

Local pain and swelling at the injection site where the botulism toxoid vaccine is administered can last up to two weeks. ^[44]

11) Equine Viral Arteritis (EVA)

Equine Viral Arteritis is a notifiable disease caused by the EAV virus. Many horses are infected with EVA at some point in their life.

The Equine Arteritis Virus enters the horse’s respiratory tract and spreads to the lymph nodes and blood, distributing the virus to organs and tissue throughout the body. ^[46]

EVA can cause pregnant mares to abort and foals to develop pneumonia or pneumoenteritis (pneumonia paired with intestinal inflammation). Stallions infected with EVA show scrotal edema and reduced fertility, semen quality, and libido. ^[46]

Horses with EVA infections also develop a fever and may show clinical signs including: ^[46]

• Depression
• Appetite loss
• Stiffness
• Leg edema (swelling)
• Conjunctivitis (pink eye)
• Teary eyes
• Edema around the eye
• Breathing difficulty
• Hives

However, many EVA infections are subclinical and go unnoticed. ^[46]

Horses infected with EVA must be quarantined. Movement of horses to and from the premises should be paused until 3 – 4 weeks after the last clinical infection. ^[46]

Transmission

The Equine Arteritis virus is transmitted in the semen of infected stallions during breeding or through inhalation of airborne viral particles. The virus can become airborne from bodily fluids, aborted fetuses or fetal membranes. ^[46]

Stallions are a natural reservoir for the virus, and it can remain in male reproductive organs, causing long-term infections with Equine Viral Arteritis. ^[46]

Treatment

EVA is treated with rest, NSAIDs, and supportive therapy such as antipyretics (fever-reducing medicine) and leg wraps to alleviate edema.

Antibiotics can also treat pneumonia or pneumoenteritis in foals. Castration is the only method to eliminate EVA from stallions. ^[46]

EVA is rarely fatal in adult horses but is usually deadly in fetuses and foals. The best way to prevent Equine Viral Arteritis is with vaccination and good biosecurity. ^[46]

Vaccine

A live attenuated vaccine against EVA is available for horses in North America. An inactivated vaccine is also available in some European countries. ^[46]

The Equine Viral Arteritis vaccine is administered through intramuscular injection.

Vaccinated horses can still become infected with EVA. Vaccinated mares may become infected when bred to persistently-infected stallions by natural breeding or artificial insemination. ^[46]

The EVA vaccine can cause abortion in mares when administered less than three months before parturition. Mares should not be vaccinated while pregnant or during the foal’s first six weeks of life. ^[46]

Foals that receive antibodies from the mare through passive transfer in colostrum will not benefit from vaccination until they reach approximately six months. By around six months, maternal antibodies are depleted and no longer interfere with vaccination. ^[46]

Although uncommon, stallions may shed the virus in urine and semen after vaccination. Some horses shed the virus for a week or up to 32 days after being vaccinated. ^[46]

To avoid transmitting the virus, stallions should not be bred for 3 – 4 weeks after being vaccinated. ^[8][46] Vaccination will not cure persistently-infected stallions. ^[46]

Vaccination Schedule

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate once per year. Stallions should not be vaccinated 3 – 4 weeks prior to being bred. Mares should only be vaccinated while open. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinated with one dose. Stallions should be isolated and not bred for three weeks after their first vaccination. ^[8]
• Blood tests should be performed on male horses that have not been gelded and horses expected to be exported to ensure they are negative for EVA antibodies immediately prior to vaccination. ^[8]

Broodmares and Pregnant Mares

• Mares should not be vaccinated for EVA while pregnant, especially during the last two months of gestation or for three weeks before they are bred unless they are at high risk for EVA. ^[8]

Foals or Weanlings under 1 year old

• Foals should not be vaccinated before six weeks of age. ^[46]
• Colts can be vaccinated with a single dose of EVA vaccine between 6 – 12 months of age. Colts should have a blood test to ensure they are negative for EVA antibodies before the vaccine is administered. ^[9]

Side Effects

The live attenuated vaccine can cause abortion in pregnant mares when administered in late gestation. Pregnant mares should not be vaccinated for EVA during the last three months of gestation. ^[47]

In rare cases, the modified live vaccine has caused fetal infection with Equine Viral Arteritis when administered to a pregnant mare. ^[46][47]

Although uncommon, the live attenuated vaccine can also cause mild fever, and a short bout of lymphopenia in which lymphocytes (immune cells) drop to a low level in the blood, putting the horse at higher risk of infection. ^[46]

Virus particles have been found in the semen of a stallion six days after vaccination. Semen should not be collected for breeding for 3 – 4 days after stallions are vaccinated for the first time. ^[46][8]

12) Leptospirosis

Leptospirosis is a bacterial disease with zoonotic potential, meaning it can be passed from animals to humans. ^[48] Leptospirosis is caused by several species of bacteria from the genus Leptospira. ^[49]

Horses with Leptospirosis commonly experience inflammation of the inner eye, which can develop into recurrent uveitis or moon blindness.

In pregnant mares, Leptospira bacteria can cause placentitis, fetal infection, abortion, or stillbirth. Infected mares can be subclinical and abort without showing any signs of illness. Infected foals may be born alive with clinical signs of leptospirosis.

Leptospirosis may also cause the following clinical signs: ^[49]

• Fever
• Appetite loss
• Hemolytic anemia (red blood cells are destroyed faster than they can be replaced)
• Blood in urine
• Jaundice
• Uveitis (eye inflammation)
• Blindness
• Kidney failure

Infected foals may also have bleeding in their lungs and struggle to breathe. Respiratory distress caused by leptospirosis is usually fatal in foals. ^[49]

Transmission

The bacteria responsible for causing leptospirosis are shed in the urine. Leptospirosis is transmitted when horses or humans come in contact with urine from infected horses or objects contaminated with infected urine. ^[48][49]

Treatment

Some species of the Leptospira bacteria can be treated with antibiotics. Supportive therapy, including fluids, antipyretics, and anti-inflammatories, can also help horses recover from leptospirosis.

However, it is difficult to treat leptospirosis in the eyes. ^[48][49]

Vaccine

The leptospirosis vaccine for horses is an inactivated vaccine administered by intramuscular injection. This vaccine protects against Leptospira interrogans serovar Pomona, the most prominent leptospirosis serotype in horses. ^[49]

The vaccine will not protect horses already infected with leptospirosis if the virus has reached the kidneys or eyes. ^[49]

Vaccination Schedule

Adult Horses over 1 year old

• Previously vaccinated: Vaccinate once per year. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate with two doses given 3-4 weeks apart. ^[8]

Broodmares and Pregnant Mares

• Previously vaccinated: Vaccinate once per year at any time. The vaccine is safe for pregnant mares. ^[8]
• Never vaccinated or unknown vaccination history: Vaccinate in two doses, with the first dose given at any time and the second administered 3 – 4 weeks later. ^[8]

Foals or Weanlings under 1 year old

• Foals are vaccinated with two doses. The first dose is given at six months, and the second is given 3 – 4 weeks after the first. ^[9]
• The leptospirosis vaccine can be safely administered to foals three months or older. ^[9]

13) Rotavirus

Rotavirus is the most common cause of diarrhea in foals under three months. Most foals are infected with rotavirus at some point before they are weaned. ^[50]

Several rotaviruses can affect animals. Rotavirus A is responsible for causing rotavirus infections in horses.

Rotavirus infections are expensive because of the costs of quarantining and treating infected foals and fatalities. ^[51]

The virus damages villi in the small intestine, reducing nutrient absorption. This causes severe diarrhea and dehydration, which can be deadly to the foal. ^[50][52]

Foals infected with rotavirus may also experience the following clinical signs. Symptoms are usually more severe in younger foals. ^[51][52]

• Fever
• Depression
• Reduced nursing
• Recumbency
• Abdominal pain
• Inflammation in the intestines

Transmission

Rotavirus A is very contagious and is transmitted in the feces of infected foals. Foals can be asymptomatic but still contagious. ^[51][52]

Foals infected with rotavirus A should be quarantined and given fluids to prevent dehydration. ^[50]

Vaccine

The rotavirus vaccine is an inactivated vaccine, which is administered intramuscularly to pregnant mares. The vaccine is given to pregnant mares so they can pass rotavirus antibodies to the foal in colostrum once the foal is born. ^[52]

The rotavirus vaccine is not completely protective but does reduce the incidence and severity of rotavirus infections. Cases of diarrhea caused by rotavirus have occurred in foals born to vaccinated mares. ^[50][52]

Vaccination Schedule

The rotavirus vaccine is administered to pregnant mares in three doses. The first dose is given at eight months gestation, with a second and third dose at four-week intervals. ^[8]

14) Snake Bite

Venomous snakes are found throughout North America and pose a threat to horses.

Poisonous snake bites can cause swelling (edema). A bite to the horse’s muzzle can endanger the horse’s life by causing the airways to swell shut. ^[53]

Snake bites can also result in pain, nausea, and weakness, and may cause the horse to go into shock. ^[53]

Equine deaths caused by snake bites are uncommon because of the amount of venom needed to kill an animal as large as a horse and because snakes sometimes bite without injecting venom. ^[53]

Treatment

If your horse is bitten by a snake, it is important to clean the wound, calm the horse to keep its heart rate down and apply a compression wrap to slow the circulation of venom in the bloodstream.

A veterinarian should be called and will likely treat the horse with antivenom, corticosteroids, antibiotics, a tetanus shot, and supportive care. ^[53]

Identifying the snake will allow the correct antivenom to be administered. ^[53]

Snake Identification

There are two categories of venomous snakes in North America: elapine snakes include cobra, mamba and coral snakes, and viperine or pit vipers include various rattlesnakes, copperheads, cottonmouths, and moccasins. ^[53][54]

Several features can help you determine whether a snake is poisonous. Venomous snakes have a triangular head that is larger than their bodies, oval pupils, fangs, and a hole just below their nose but above the mouth.

Non-poisonous snakes have a round head that is the same size as their body, small teeth, and round pupils. ^[53]

Vaccine

Vaccinating your horse against snake bites is advised if you live in an area where venomous snakes are present or if you plan to travel to an area known to have snakes. Discuss vaccination with your veterinarian. ^[55]

An inactivated toxoid vaccine is available for horses over four months old. Unlike most intramuscular equine vaccines, the snake venom vaccine should be administered in the horse’s pectoral muscles. ^[55]

The vaccine is designed to protect against the venom of the Western Diamondback rattlesnake. It is also effective against the sidewinder, timber, massasauga, copperhead, and other rattlesnakes, excluding the Mojave rattlesnake. ^[55]

The vaccine may not fully protect horses in every case and is conditionally licensed. ^[55]

Vaccination Schedule

Horses over 4 months old

• Previously vaccinated: Vaccinate every six months. ^[55]
• Never vaccinated or unknown vaccination history: Vaccinate in three doses given one month apart. ^[55]

Broodmares and Pregnant Mares

The safety of this vaccine for broodmares and developing foals is unknown. Ask your veterinarian for information on its use in pregnant mares. ^[55]

The snake bite vaccine is still undergoing tests for efficacy and potency. ^[55]