Foal Diarrhea Caused by Lawsonia

September 24, 2007 (published) | August 27, 2012 (revised)

Today on Texas Vet News I am going to talk about a fairly new intestinal disease of young horses caused by the bacterium Lawsonia. The disease affects weanling foals from 3 to 13 months of age and symptoms include fever, lethargy, a decreased appetite, diarrhea, colic and weight loss. Another symptom that appears to be common with this disease is edema or fluid that develops under the skin due to a decrease in protein absorption from the intestinal tract.

Dr. Nicola Pusterla indicated at the AAEP convention that it is important to identify sick foals early and separate them from the rest of the herd to prevent transmission of the bacterium. Any foals that only have mild edema, a slight fever or mild decrease in appetite should be examined by your veterinarian. An ultrasound exam of the foal's intestine can reveal the increased thickness that is common with Lawsonia, and fecal and blood tests can be used to make the diagnosis. Most foals will need to be treated with antibiotics, anti-ulcer medication, and intravenous fluids as well as intravenous plasma to replace lost protein. Other foals that have been exposed should be watched closely and have their protein levels checked as low protein levels in the blood are typical of this disease. This disease has become common and has become endemic on many farms, meaning the organism is present on the farm and disease is likely to recur. A vaccine approved for swine has been used experimentally on foals and it was effective in preventing the disease. Most foals affected with Lawsonia do well with treatment as long as the diagnosis is made early and aggressive treatment is used.

VIN News Service commentaries are opinion pieces presenting insights, personal experiences and/or perspectives on topical issues by members of the veterinary community. To submit a commentary for consideration, email

Information and opinions expressed in letters to the editor are those of the author and are independent of the VIN News Service. Letters may be edited for style. We do not verify their content for accuracy.