Bacterial diseases are quite common in the horse, with skin and gastrointestinal (GI) infections being the most frequently-occurring. Less frequently, bacterial infections will affect a horse’s respiratory tract. Bacterial skin diseases (pyoderma) are most often caused by Staphylococcus species, usually Corynebacterium pseudotuberculosis or Dermatophilus congolensis. The most common clinical signs associated with these infections are crusts, papules and abscesses.¹ The most common symptom of GI infections in horses is diarrhea.   

More often than not, a horse’s immune system is able to overcome bacterial intrusions without the horse developing clinical signs of sickness. In a majority of cases, bacterial disease occurs when the horse’s immune system has been weakened and bacteria are able to replicate and spread throughout the horse’s body. 

Healthy adult horses are typically resistant to most bacterial disease, with foals and geriatric horses being at greater risk of developing bacterial disease due to the fact that their immune systems are not as robust as those of younger horses.² Bacterial infections are also more common in horses that travel or frequent stables where many horses congregate. 

When a horse shows clinical signs of bacterial disease, the source of bacteria is usually often contaminated water, food or feces that are subsequently ingested. In the case of some bacterial infections (e.g., skin, respiratory), the causative agent may be present in the environment. Tick-borne diseases are also a concern; these can be difficult to diagnose, because these ailments (e.g., Lyme Disease, Equine piroplasmosis, Anaplasmosis) often have more than one symptom.

Bacterial Diseases of the Horse

Some common bacterial diseases of horses include:

Potomac horse fever (Neorickettsia risticii) causes fever, mild colic and diarrhea. It can affect horses of all ages and can cause pregnant mares to miscarry. Horses can become infected when they accidentally eat aquatic insects that contain the infected N. risticii flukes.

Salmonella (Salmonella spp.) can cause diarrhea in horses, and younger horses are more at risk of infection. More severe cases of salmonella infection can lead to inflammation of the intestines or even death. Horses are most often infected by ingesting contaminated feed or water. 

Strangles (Streptococcus equi) is a highly contagious disease of horses. Symptoms include fever, abscesses in the upper respiratory tract, discharge of mucus from the nose and swollen lymph nodes. A horse may also have difficulty swallowing and may breathe noisily or heavily.

Cryptosporidiosis (Cryptosporidium spp.) is a parasitic disease which is usually spread via the ingestion of infected feces. Horses infected with cryptosporidium often do not evidence signs of illness, although pre-weaned foals appear to be more likely to experience diarrhea than weanlings, yearlings and older horses.³

Lymphangitis is an inflammation of the horse’s lymphatic channels, and can be caused by infectious or noninfectious agents, which can include bacteria, mycobacteria, viruses, fungi, and parasites.^3,4 Symptoms include small lumps or swelling, sores on the fetlock and painful inflammation. 

Tetanus (Clostridium tetani) is caused by a toxin produced by the C. tetani bacterium; this blocks nerve signals, causing severe contraction of muscles and extreme responses to stimuli. Symptoms may include stiffness of the muscles of the jaw, neck and hind limbs. 

Lyme disease is a tick-borne disease that is transmitted by ticks carrying the organism Borrelia burgdorferi. Lyme disease has a variety of symptoms, including stiffness, lameness, muscle tenderness, muscle wasting, lethargy, behavioral changes, skin sensitivity and weight loss. 

Oral Doxycycline Hyclate for Horses

Doxycycline hyclate is broad-spectrum antibiotic composed of a semi-synthetic tetracycline derived from oxytetracycline. It is commonly used in small animals to treat a variety of infections caused by several different microorganisms, including Borrelia spp, Leptospira spp, Rickettsia spp, Anaplasma spp, Ehrlichia spp, Chlamydia spp, Mycoplasma spp, Bartonella spp, and Bordetella spp. In horses, it is often used for treating bacterial infections, including Potomac Horse Fever and Lyme disease.⁵

There are currently no FDA-approved veterinary doxycycline products available, but the drug’s pharmacokinetic parameters as compared with either tetracycline or oxytetracycline make it a preferable choice to use in animals when a tetracycline is indicated.⁵

Where to buy Doxycycline Hyclate

Doxycycline is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. DOXYCYCLINE HYCLATE 5 GM/SCOOP ORAL POWDER, 60 SCOOPS (20CC SCOOP) by NexGen Pharmaceuticals is indicated for bacterial infections in the horse. It has similar activity to other forms of tetracycline against susceptible organisms however, some strains of bacteria appear to be more susceptible to doxycycline.

Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹White, S. Equine Bacterial and Fungal Diseases: A Diagnostic and Therapeutic Update. Clinical Techniques in Equine Practice, Volume 4, Issue 4, December 2005, Pages 302-310.

²Panchaud Y, Gerber V, Rossano A, Perreten V. Bacterial infections in horses: a retrospective study at the University Equine Clinic of Bern. Schweiz Arch Tierheilkd. 2010 Apr;152(4):176-82. doi: 10.1024/0036-7281/a000040. PMID: 20361396.

³extension.org.

⁴cdc.gov.

⁵Plumb’s Veterinary Drugs.