There are numerous bacterial infections that horses experience. Some are very common and frequently encountered, while others occur much more rarely. Bacterial disease occurs when a horse’s immune system cannot sufficiently combat bacteria and it becomes able to replicate and spread in the horse’s body. This is generally due to the immune system being compromised (by an existing viral or fungal infection, for example) or from the introduction of a high bacterial load. 

There are several bacterial pathogens that most frequently cause disease in horses. Among these are Tetanus, Potomac Horse Fever, Salmonella, Strangles and E. Coli.

Equine Intestinal Infections

Salmonella is the most widely diagnosed infectious cause of diarrhea in horses. In mild cases of salmonella and in the early stages of infection, the horse may have little or no diarrhea, but may suffer from a fever as well as stomach discomfort. In more severe cases, the horse will have watery, foul-smelling diarrhea. The horse will appear uncomfortable and may repeatedly get up from a lying position as it tries to get comfortable.¹ The horse may also evidence:

• Depression
• Lack of appetite
• Tail twitching
• Straining
• Rectal prolapse
• Dehydration
• Discoloration of gums

Potomac horse fever (PHF) is also called monocytic ehrlichiosis and equine ehrlichial colitis.¹ This disease is more commonly seen in the eastern United States, although it can occur throughout the country and can be mild to severe and life-threatening. The clinical signs of PHF can vary however, anorexia, diarrhea, colic and fever are the most common symptoms. 

Endometritis in Mares

In horses, endometritis is called an “invisible” disease because it often goes undiagnosed until it has caused significant damage.² Endometritis affects the endometrium (lining) of a mare's uterus, causing it to become inflamed and making it an inhospitable environment for sperm and embryos. A major cause of infertility in horses, endometritis affects up to 15% of broodmares.

Quite often, mares that cycle but repeatedly fail to conceive are found to have infections in their reproductive tracts. In nearly all cases, this will be the result of endometritis.³ The reduced fertility associated with endometritis has been recognized for many years, and is due to the resulting unsuitable environment within the uterus for the developing conceptus.² In some cases, the endometritis causes early regression of the corpus luteum. This usually occurs as a result of microbial infection, but it also can be due to non-infectious causes. 

There are several classifications for equine endometritis:

• Endometrosis (chronic degenerative endometritis)
• Chronic infectious endometritis
• Mating-induced endometritis (delay in uterine clearance)
• Venereal infection³

The uterus of the mare is generally well-protected in the physical sense. However,  contaminants can still enter the uterus during mating or artificial insemination, as well as during estrus or veterinary procedures.² The uterine lumen of the normal fertile mare is sterile despite the fact that the reproductive tract is contaminated with bacteria from the act of breeding, foaling, and veterinary procedures. Mares with defective vulval conformation can suck air and bacteria into the vagina, which can develop into endometritis.³

The uterus responds to bacteria invading the reproductive tract with a rapid influx of neutrophils. Normally these neutrophils kill the bacteria rapidly, and the inflammatory byproducts are mechanically removed and the endometritis resolves itself (returns to normal). Failure to resolve this inflammation results in the “susceptible” mare.^3,4

A diagnosis of endometritis can be made by collection of concurrent endometrial swab and smear samples during early estrus for bacteriological culture and cytological examination, respectively.⁴

Enrofloxacin for Equines

Enrofloxacin is a veterinary oral and injectable fluoroquinolone antibiotic that is effective against a variety of pathogens, although it is not effective against anaerobes. The literature holds that its use should be avoided in young, growing animals because of the potential negative impact on cartilage development.

In the past, there had been reluctance among horse owners in using compounded enrofloxacin to combat endometritis, but in recent years, the success of this and other compounded medications have led to widespread acceptance among horse owners and veterinarians, with researchers agreeing that enrofloxacin suspensions are useful in the treatment of bacterial endometritis.⁴

Where to buy Enrofloxacin

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

This product carries numerous 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.

¹wagwalking.com.

²Lesté-Lasserre, C. Endometritis in Horses Explained. In: The Horse, Nov 1, 2010. https://thehorse.com/150681/endometritis-in-horses-explained/

³Pycock, J., DVM. Endometritis Classifications and Treatment. In: The Horse, Apr 1, 1999. https://thehorse.com/14445/endometritis-classifications-and-treatment/

⁴Beckstett, A. Compounded Enrofloxacin: Safe and Effective for Use in Mares. In The Horse, Apr 5, 2015. https://thehorse.com/111731/compounded-enrofloxacin-safe-and-effective-for-use-in-mares/