HomeHorseSalmonellosis in Horses: A Disease Causes Late Abortion in Mares

Salmonellosis in Horses: A Disease Causes Late Abortion in Mares

Equine contagious abortion is a specific disease of horses caused by Salmonella equi and is characterized by abortion in mares, testicular lesions in the stallion, and septicemia in newborn animals. Salmonellosis in horses is a common problem in the breeding stock of horses that causes late abortion. I shall discuss the essential information on this disease for horse breeders and veterinarians in my article.

Causes of Salmonellosis in Horses

Salmonella abortus equi is the causative organism and can be isolated from affected animals. The organism is non-spore-forming, motile, gram-negative rod-shaped bacteria. The organism is aerobic and facultative anaerobic and grows abundantly on standard laboratory media. The bacteria colonies on the agar plate are small, round, slightly elevated, and glittering, which become finely granular in structure as they grow. Older colonies are dry, membranous, and the entire colony can be pushed along the surface of the agar. These colonies are irregular and appear like rosettes with a wrinkled surface resembling tanned alligator’s or lizard’s skin.

Horse Behavior Mare

Epidemiology of Equine Contagious Abortion

The infection appears to be restricted to horses and donkeys. In the early 1900s, this disease was widely reported nowadays is less encountered. This organism causes abortion in mares to occur sporadically. It is one of the less common causes of either abortion or septicemia in horses. Natural infection may be due to ingestion of foodstuffs contaminated by uterine discharges from carriers or mares recently aborted. Stallions also transmit the disease during the time of service. The infection may be stayed in the uterus and causes repeated abortions or infection of subsequent foals. 

Pathogenesis of Salmonellosis in Horses

When infection occurs by ingestion, transient bacteremia is followed by localization in the placenta, resulting in placentitis and abortion. Foals carried to term are probably infected in utero or soon after birth by ingestion from contaminated teat or through the umbilicus. 

Examination of Mare

Clinical Findings of Equine Contagious Abortion

The usual clinical finding of the disease are:

  • Abortion usually occurs during the 7th or 8th month of pregnancy.
  • The abortion may show no signs of illness or a temperature rise (104° F) accompanied by colic, diarrhea, and a purulent chocolate color vaginal discharge.
  • Retention of the placenta and contagious metritis are common sequelae and may cause serious illness.
  • Live foals may be born from mares infected with S abortus equi.
  • These foals may be weak, emaciated, and die of septicemia within hours after birth.
  • Other foals appear entirely normal but within a few days develop a purulent naval infection and pyoarthritis or both.
  • Pyoarthritis may develop in 2 to 3 weeks after birth.
  • In infected stallions, there is fever, edematous swelling of prepuce and scrotum, and arthritis.
  • Hydrocoele, epididymitis, and inflammation of the tunica vaginalis are followed by orchitis and testicular atrophy.

Mare Management

Diagnosis of Salmonellosis in Horses

The organism can be isolated from the infected placenta, uterine discharge, aborted fetus, and joints of foals with pyoarthritis.

  • Diagnosis is confirmed by isolation of causative bacteria and identification of the organism.
  • History and clinical signs.
  • The organism can be present in the cervical discharge of mares for only a few days to 3 weeks. Therefore, samples should be taken as early as possible.
  • The positive agglutination test in mares also helps in the identification of the disease.

Necropsy Findings of Equine ContagiousAbortion

  • The fetal membrane will show diffuse, hemorrhagic placentitis.
  • The chorion becomes edematous, and necrotic appears as dirty grey and thickened plaques.
  • The pleural and peritoneal cavities of the fetus contain an excessive amount of cloudy or hemoglobin-tinged fluid.
  • Pyoarthritis is found in foals dying in the later stages.

Treatment of Salmonellosis in Horses

Equine contagious abortion is a bacterial disease, and the disease can be cured by treatment with effective antibiotics.

  • In foals with septicemic Salmonellosis, treatment must be given 6 hours and accompanied by supportive therapy. Favored antibiotics are Gentamycin @ 250 mg IV twice daily, Ampicillin 1 gm 6 hourly, and Chloramphenicol @ 20 mg/kg body weight IV 6 hourly.
  • In adult horses, parenteral treatment with Trimethoprim and Sulfadoxine @ 1mg/kg body weight daily, ampicillin 2-7 mg/kg body weight daily IM, and Chloramphenicol 2-4 mg/kg body weight IM is recommended. 
  • Nitrofurazone @ 20mg/kg body weight daily in water given by stomach tube for 3 to 5 days is also recommended.
  • Sulfathiazole 50 mg/kg body weight of the sodium salt as 5-10% solution has been used for treatment, but healthy animals will typically get rid of infection themselves.

Prevention of Equine Contagious Abortion

The disease can be prevented by scheduled vaccination in pregnant mares. The methods of schedule vaccination are as follows:

  • First vaccination on confirmation of pregnancy 10 ml IM ( about 35 days of pregnancy).
  • Second vaccination ten days after first vaccination 10 ml IM (about 45 days of pregnancy).
  • Third vaccination ten days after second vaccination 20 ml IM (about 55 days of pregnancy).
  • Fourth vaccination 60 days after third vaccination 20 ml IM (about 115 days of pregnancy).
  • Fifth vaccination 60 days after fourth vaccination 20 ml IM (about 175 days of pregnancy).
  • Sixth vaccination 60 days after fifth vaccination 20 ml IM (about 235 days of pregnancy).

When vaccination is restored for the first time or after a long interval, all broodmares will be sero-tested before vaccination. Only those who are opposed to the test will be vaccinated. 

All stallions should be sero-tested before the onset of the breeding season and once in a quarter. Mares showing doubtful positive titer will not be brought on the vaccination schedule. Those that are positive or show an ascending titer to the 2nd or 3rd test will be segregated and treated.

Concluding Remarks on Salmonellosis in Horses

A successful horse breeding farm wishes to get a foal each breeding mare at each season. Broodmares that abort at the later stage of pregnancy bears a considerable loss to the breeder. Salmonellosis is one of the causes of late pregnancy in mares. To prevent this condition, broodmares and stallions must be tested regularly before taking for breeding. 


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