These are several moderate- to serious bacterial infections of horses for which tetracycline is the antibiotic of choice. Tetracycline is a bacteriostatic with a broad spectrum of activity against many gram-positive and gram-negative aerobes.¹

Equine granulocytic anaplasmosis (EGA, commonly anaplasmosis) is an infectious, noncontagious seasonal disease of horses. It was originally recognized in the US in northern California, but is now seen in many states where tick vectors are present. This disease also occurs in Europe, Africa, and South America. The causative rickettsial agent of anaplasmosis in horses is Anaplasma phagocytophilum.² This organism has a wide host range; naturally occurring infections have been seen in all equines, dogs, llamas, rodents, and humans.

“Severity of signs of EGA varies with age of the horse and duration of the illness. Signs may be mild. Horses <1 year old may have a fever only; horses 1–3 years old may develop fever, depression, mild limb edema, and ataxia. Adults, and particularly geriatric horses, may exhibit fever, partial anorexia, depression, reluctance to move, limb edema, petechiation, and icterus.”²

Potomac Horse Fever is caused by Neorickettsia risticii and was originally described in 1979 as a sporadic disease affecting horses residing in the eastern US near the Potomac River. Since then, the disease has been identified in other areas of the United States and Canada. Like EGA, the disease is seasonal, occurring between late spring and early fall in temperate areas.³

Clinical signs of Potomac Horse Fever can include fever, mild to severe diarrhea, laminitis, mild colic, and decreased abdominal sounds. Pregnant mares with this disease have been known to abort infected fetuses, although foals appear to have a low risk of contracting the disease. Mortality rates have been reported between 5% and 30%. 

Lyme disease (which is named after Lyme, Connecticut, where it was first identified in the 1970s), is the most common vector-borne disease in the US, according to the US Centers for Disease Control (CDC). It is caused by the organism (Borrelia burgdorferi). Most human cases are reported to occur in the northeastern, mid-Atlantic and north-central states, with fewer in the Pacific and southern states.

Signs of the disease often don't emerge for five to six weeks after a tick bite. Some commonly seen signs in horses include:

• Stiffness in the large, sporadic lameness
• Generalized tenderness (hyperesthesia)
• Behavioral changes
• Low energy
• Low-grade fever
• Joint swelling⁴

Persistent Lyme disease has also been linked to weight loss, chronically stiff and swollen joints, neurological problems and inflammation of the eyes.

Proliferative enteropathy is a disease of foals caused by the intracellular organism Lawsonia intracellularis. The organism causes proliferation of infected enterocytes, resulting in thickening of the intestinal epithelium, most often the small intestine. This disease affects mainly weanling foals and causes fever, lethargy, peripheral edema, diarrhea, colic and weight loss.^1,3

Tetracycline for Horses

Tetracyclines come in several forms, and are the most commonly used medications for the treatment of above described diseases in horses. Tetracyclines are often used in combination with sulfa antibiotics to treat bacterial respiratory infections such as pneumonia and pleuritis in racehorses and foals. Doxycycline is another tetracycline antibiotic prescribed by veterinarians; oxytetracycline is a time-released form. It is also available in topical ointments for use in eyes and on the skin.³ Injectable oxytetracycline is occasionally given to young foals born with contracted tendons because it rapidly binds calcium, allowing for muscle and tendon relaxation. It is also used for respiratory disease in older foals.⁴

Where to buy Tetracycline

Tetracycline is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. 

This product carries several potential drug interactions. 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.

¹Ohio State Press Publications.

²Merck Veterinary Manual.

³aaep.org.

⁴practicalhorsemanmag.com.