Incidence of weanling diarrhea grows in North America’s young horse populations

A relatively new intestinal disease is being seen on some horse farms, affecting weanling foals. Proliferative enteropathy (PE), a term that means intestinal disease caused by a multiplying pathogen, in this instance is caused by an organism called Lawsonia intracellularis. This may be an emerging disease, or possibly one that is now being recognized during the past 12 years or so.
    PE occurs most commonly in foals four to seven months of age, and foals seem susceptible at weaning time. This transmissible disease affects several species including pigs and hamsters. It is found worldwide and is now reported in an ever-increasing range of hosts.
    Simon Peek, department of large animal internal medicine at the University of Wisconsin, has seen a number of young horses with this type of diarrhea.
    “It seems to be a growing problem. It occurs in areas of North America where there are dense horse populations of that age group,” he says.
Finding PE
    The most common clinical signs of PE include rapid weight loss, depression, subcutaneous edema or swelling under the skin, diarrhea and colic. Severely affected foals often have a rough hair coat and pot-bellied appearance with extremely poor body condition, though some may die before they look this poorly.
    PE can lead to death within just a few days or may retard the growth of foals that survive. Some foals suffer respiratory tract infection along with intestinal infection.
    “It can sometimes be difficult to divide one problem from the other. These foals are at an age where we see contagious respiratory disease anyway. PE is not the cause of the pneumonia, but the respiratory problem could be a secondary invader. The body is compromised and more vulnerable,” says Peek.
    Use of ultrasound to check the foal’s abdomen may reveal thickening in the wall of the small intestine. It cannot absorb fluid properly, leading to diarrhea.
    Fecal samples can be checked using PCR, or polymerase chain reaction, analysis. This analysis enables investigators to identify specific DNA sequences of the pathogen molecule.
    Other means of diagnosis involve serology, which is measuring serum antibody titers or using serologic reactions to detect antigens.
    Diagnosis of PE may also be confirmed based on presence of intracellular bacteria within epithelial cells of the intestinal mucosa, which is the mucous lining of the intestine.
When to watch
    “This disease is not a problem in nursing foals, but hits at weaning time,” says Peek. “It is possibly triggered by stress of weaning. We’re not sure what other factors figure into it, except that it’s a contagious disease.
    “It’s not unusual to have more than one case on a farm in one season. On occasion we have screened herd mates of an affected weanling, using serology, to find evidence of infection in clinically normal animals that we eventually treat.”
    The bacteria are spread via feces of infected foals and can live for up to two weeks in the environment. It’s wise to isolate a sick foal and thoroughly clean the stall where he was kept during treatment and recovery, says Peek. People treating the foal should take precautions to not carry the bacteria to healthy foals on boots or clothing.
Treating PE
    Since the bacterium lives and multiplies in cells of the intestinal lining, treatment should include an antibiotic that has good penetration into the cells. The veterinarian may choose a drug like erythromycin estolate, given orally every six to eight hours. This drug may be used alone, or in combination with rifampin. The latter is given orally, once a day for a minimum of 21 days. Chloramphenicol, given by mouth every six hours, is also effective. Other antibiotics that have also been used include chlortetracycline, penicillin and ampicillin.
    If the intestine cannot absorb fluid and nutrients, the foal may need I.V. feedings. Foals with extremely low blood levels of protein may need intravenous plasma. Some foals may benefit from ulcer medication as well.
    PE can quickly be fatal unless treated appropriately. If treated early, however, the foal usually makes rapid improvement in attitude and appetite. Signs of colic and diarrhea subside, and the foal starts eating and gaining weight again.
    Heather Smith Thomas is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.