How To Tell If Your Horse Is Sick | An Overview Of Common Horse Diseases And Ailments

Horse owners love their horses and want to do everything they can to ensure they are in good health. That’s why it’s important to know the common ailments in horses and be able to recognize the signs that your horse may be sick. After all, taking your horse to the veterinarian is no quick and easy trip and getting a doctor to come out to you can be expensive. That’s why here we will cover the most common horse diseases and health issues, how to recognize them, and how to prevent them in the first place.

Signs of a Healthy Horse

Before we can recognize a sick horse, we have to first know the signs of a healthy horse to establish a baseline. A healthy horse will have a bright and alert attitude, a consistent appetite, clear and clean eyes and nose, a full and shiny coat, strong and cold feet, good hydration (5-10 gallons of water per day), healthy manure (8-12 times per day), wheat colored and clear to slightly cloudy urine, and an ideal body condition score of 4-5 (using the Henneke scoring system). Remember, systematic observation is key. Horse owners must be vigilant in order to catch signs of illness early. Look for any changes in eating habits (sick horses will often go off feed) and behavior. Normal behavior changes are slow and happen over a long span of time. If you see any sudden changes in behavior it is best to visit a veterinarian to check for any medical issues.

It is also essential to know the normal vital signs of your horse in order to tell if there is a change. Below are the normal vital signs of an adult horse at rest. Keep in mind the these will vary according to age and workload. A change in any of these could be a sign of fever, illness, or pain.

• Respiration: 12-16 breaths per minute
• Rectal Temperature: 100.5°
• Heart Rate (Pulse): 35-40 beats per minute

Infectious Diseases of the Horse

Now that we have established a baseline of what a healthy horse looks like, let’s take a look at the most common diseases found in horses. Many of the infectious diseases that plague horses come from bacteria and viruses. It is important to know both the true name (bolded) and the common name (italics) of each disease as they are often used interchangeably.

Encephalomyelitis (Sleeping Sickness) is a viral disease that attacks the brain and central nervous system of the infected horse. It is often fatal and has three strains: Eastern (EEE) (the most deadly), Western (WEE) (the most common), and Venezuelan (VEE) (very uncommon in the U.S.). It is transmitted by certain bloodsucking insects found in swampy areas such as mosquitos. Infected horses will display a loss in appetite, fever, overly compulsive behavior, and circling or head pressing. Fortunately, this disease is easily preventable with a vaccine that should be administered annually or twice annually. All horses should be vaccinated against EEE and WEE, but those living within 40 miles of the Mexican border should also be vaccinated against VEE.

Equine Infectious Anemia (EIA/Swamp Fever) is another potentially fatal viral infection that leads to anemia. It is transmitted by blood which can occur either through bloodsucking insects or passed from mare to foal across the placenta. One very troubling aspect of EIA is that once infected, the horse can become a carrier for life and therefore poses a risk to other horses. Any infected horse is either strictly isolated for life or humanely euthanized. Infected horses will display a loss in appetite, fever, lethargy, and rapid weight loss. Unfortunately, there is NO VACCINE and NO CURE for this important disease. The only means of control is by annual Coggins blood test which is needed for transport across state lines as well as boarding, showing, competition and other events. Luckily, EIA is very rare in the U.S.

Strangles (Distemper/Shipping Fever) is a bacterial respiratory disease caused by the streptococcus equi bacteria. This highly contagious disease is transmitted through nasal secretions and fomites or contaminated objects along with shared food or water, although flies are also believed to play a role in transmission. Strangles is characterized by the formation of large abscesses in the horse’s lymph nodes (glands under the jaw) although fever, nasal discharge, cough, and trouble swallowing are also clinical signs. Prevention of strangles is possible but complicated. There is a vaccine, but it can result in serious side effects such as a fatal immune system reaction called purpura hemorrhagica. Many veterinarians only recommend vaccination if the horse is in a high exposure risk environment such as a barn where strangles has already been diagnosed. This is because the risks for vaccination are significantly increased if the horse already has a large number of antibodies circulating in his blood stream. Therefore, an antibody test may be recommended before vaccination. If vaccinating, annually just before fly season begins or 2 or more weeks before exposure is best.

Tetanus (Lock Jaw) is the same bacterial infection most people are familiar with. It is caused by the bacteria Clostridium tetani which leads to life-threatening paralysis and asphyxiation. It is only transmitted when the bacterium bedded in the soil and environment enter the horse’s body through open wounds or punctures. Afflicted horses will display muscle spasms, excessive fever, and increased sensitivity to noise and movement. The best prevention is annual vaccination which should be re-administered if the horse suffers a wound and has not received the vaccine within the last 6 months. Be careful when vaccinating your horse for tetanus yourself however, because there are two vaccines available. Be sure to administer the tetanus toxoid as this is designed to prime your horses immune system. The alternative, tetanus antitoxin, is a direct antibody source only for use in an injured animal with no vaccine history.

West Nile Virus (WNV) is a virus that attacks the horse’s nervous system and causes inflammation in the brain and spinal cord. It is carried by birds, and although there is no evidence that horses can transmit the disease to each other directly, mosquitos are able to transmit to other horses, humans, and other animals. Clinical symptoms are primarily neurological and include stumbling, weakness, ataxia (decreased coordination), toe-dragging, muscle spasms, and paralysis. It is vital to vaccinate against WNV annually to twice annually as one in three horses will die if infected.

Equine Viral Rhinopneumonitis (rhino/equine herpes virus/EHV) is a multi-form, respiratory disease that causes neurological and respiratory issues as well as abortion in pregnant mares. It is passed from horse to horse through the air making it highly contagious. Although it is not 100% effective against all neurological forms, all horses should be vaccinated to reduce their chances of becoming ill. However, immunity is short-lived and only lasts 2-3 months. Additionally, as much as 80% of horses are carriers (harbor without becoming ill) of this virus and vaccination will have minimal benefit for these horses. Pregnant mares should still be vaccinated at 5, 7, and 9 months of gestation to prevent abortion.

Equine Protozoal Myeloencephalitis (EPM/Possum disease) is another potentially fatal disease the affects the horse’s spinal cord. It is caused by protozoa spread by possums, and causes a wide range of symptoms including ataxia, difficulty chewing, seizures, and lameness. Due to the prevalence of possums in certain parts of the country, as many as 70-80% of horses in these areas have antibodies against EPM, yet never show signs of infection. Unfortunately, vaccine effectiveness has not been well established, and vaccinating could complicate diagnosis if the disease is contracted. Diagnosis is already difficult because it requires the extraction of antibodies in the blood and fluid surrounding the spinal cord and vaccination stimulates these antibodies as well. If you decide to vaccinate at all, do so annually.

Internal and External Parasites

In addition to bacterial and viral infections, internal and external parasites also plague horses, and owners need to ensure that these parasites are controlled. Unfortunately, all horses are at risk for parasites through ingestion of larvae and eggs when grazing on pasture. Other parasites torment the host horse by clinging to the face, biting the skin, as well as laying eggs on the body. Signs to look for that indicate parasitic infestation are colic, diarrhea, potbelly, dullness in coat, as well as weight loss and debilitation due to the parasites feeding on the intestinal tract stealing essential nutrients from the horse.

Common internal parasites include:

• Ascarid – the largest of roundworms that fill the gut in mostly young foals
• Bots – lay their eggs on horse’s legs which are then ingested causing stomach damage via larvae attachment
• Large Strongyles – nematodes that damage arteries by internal migration and can cause death
• Small Strongyles – most common nematodes that lodge in intestines and are often resistant to dewormers
• Pinworms – exit through the anus causing itching at the tail which aren’t directly damaging but cause irritation which leads tail rubbing

Control of internal parasites is done mostly through the administration of anthelmintics (deworming medication). This is most often done through an oral paste that most horse owners are capable of giving, but sometimes given via a stomach tube which should only be passed by a veterinarian. Paste dewormers include Ivermectin, Safe-Guard, Quest, and Strongid. There are also daily feeding granules such as Strongid C.

Diagnoses of parasite infestations is commonly done through a fecal egg count in which a veterinarian will count the number of eggs being shed in the feces. However, these tests can be an inaccurate assessment of the horses overall parasitic burden due to the fact that eggs will not be detectable during the larval migration and other stages of the parasites lifecycle. This means that fecal egg count results can be negative even though the actual parasitic burden is high. There are other tests available for parasite detection, but none of these other methods are practical for routine use. Therefore, the best means of parasite control is prevention. Deworm regularly, an average of 3-4 times per year (variable depending on stocking rate, pasture control, age of horse, etc.), and rotate between classes of dewormers utilized to prevent resistance issues.

Common external parasites include:

• Flies
• Ticks
• Lice
• Mosquitoes

These can be controlled using fly sprays, fly wipes, fly sheet blankets, and barn sprayers. Be sure to reduce reproduction by removing all stagnant water from the premises.

Nutrition Related Ailments

There are two primary health problems that may be associated with your horse’s nutrition. The most notable of these is Colic. Colic is a pain in the intestinal area of the horse ranging from mild to very severe, requiring extensive surgery. Unfortunately, colic is the number one cause of death in horses and recognizing the signs and types will allow you to take action to prevent death from happening should your horse colic.

Types of colic include:

• Gastric Torsion or Gastric Dilation and Volvulus (GDV) is the twisting of intestines
• Impaction of feedstuffs in the gut; often associated with lack of sufficient water
• Gas associated colic
• Telescoping of the intestine
• Intestinal parasite colic

Recognizing colic can be difficult as the prey animal nature in horses leads them to hide ailments better than people or other animals. As with any sickness, constant vigilance is the key. Look for any rapid changes in behavior or appetite. The most common symptoms of colic are refusal to eat, increases in heart rate and respiration, attempting to roll, and looking at its side due to pain. If you see any of these in your horse seek immediate help from a veterinarian as time is a serious factor when colicing. Additionally, attempt to keep your horse from rolling by walking them around slowly.

The second nutrition related ailment is Laminitis or Founder. Laminitis is a very serious lameness which occurs when the bone of the hoof rotates away from the hoof wall and sinks into the sole causing pain and irreversible damage in many cases. Laminitis has many causes, one of which is the feeding of too many carbohydrates. This often occurs from improper feedings or when a horse breaks into a feed room. If left unattended a horse can eat half a bag of grain which will result in laminitis as horses cannot vomit. Other causes include systematic infections, too much work on hard surfaces, or pastures that are too lush and rich in early spring. It’s also not uncommon for the cause of laminitis to be unknown. Symptoms to look out for include heat in the hoof and lameness in the front hoof (horses will often take weight off their back hoof but never their front). Remember, prevention is key! Safely store and lock up grain and limit grazing times in lush pastures. If you see any of these signs in your horse seek immediate veterinary intervention. Treatment is often the administration of mineral oil into the stomach via nasogastric tube.

To Summarize

There are many many many ailments and infections that can inflict horses. This is one of the harsh realities of horse ownership. Compared to other pets we love, horse health problems abound. For this reason, it is crucial as a horse owner that you learn how to tell if your horse is sick and how to handle (and more importantly prevent) these health issues should they occur.