Lawsonia intracellularis is a type of bacteria associated with the disease Equine Proliferative Enteropathy (EPE), and for years, it has been a tricky foe for veterinarians. The bacteria, which tends to impact young horses, thickens the intestinal wall, preventing horses from properly absorbing their food. EPE causes puffiness in the jaw, leg or abdomen, lethargy, fever, diarrhea, poor coat, and weight loss.
Lawsonia has been tricky for veterinarians and managers to nail down, as scientists still aren't sure how it gets introduced to the young horse's system. It's generally thought the bacteria is shed in feces, but no one is sure where or how long it may live in the environment in order to be reintroduced to the horse.
As a veterinarian who spends a lot of time on Central Kentucky breeding farms, Dr. Laurie Metcalfe told attendees at Rood and Riddle's annual client education seminar she's been hoping for a better weapon against Lawsonia and EPE for years. Although the disease most commonly impacts foals between four and seven months, Metcalfe said she has found it in 2-year-olds.
“We think the stress of weaning at the same time as their maternal antibodies wearing off is why this age group is the most susceptible,” she said. “This can be a very, very devastating disease as far as trying to get these foals to the sale. We will lose some of these foals as well because it impacts them so profoundly.”
Recently however, veterinarians have gotten positive results from using a vaccine aimed at lawsonia in pigs. Metcalfe said the vaccine is given in two intrarectal doses 30 days apart, typically in August/September/October. Previous studies had indicated it was safe to use off-label in horses so Rood and Riddle veterinarians decided to offer it to clients to learn how effective it could be.
“I sadly have dealt with this disease probably more than most. If there was a chance something could prevent this disease, we wanted to try it,” said Metcalfe.
In 2017-18, the clinic vaccinated over 150 foals on farms where there was a consistent history of the disease in previous years, which Metcalfe considered “endemic” farms. None of the foals receiving the vaccine developed EPE. Metcalfe said 2017 was a “profound year” for lawsonia cases, which increased her confidence the foals who were vaccinated likely did come in contact with the pathogen and resisted infection.
She cautioned the field work was not done with the intent the results should be published in a scientific journal, and veterinarians did not therefore have the degree of control over variables like housing or management that would be required for an academic study.
“My experience is extremely subjective [but] my overall impression is it is definitely safe and I would, without hesitation, recommend it to any endemic farm,” she said. “The non-endemic farms are going to have to weigh the cost effectiveness. It's a little over $70 a dose and you do it twice, so if you have 150 foals it may not be worth it for you.”
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