Ask the Vet: Foals

Answered by, Madison Seamans, DVM, MS, Kuna, ID
Courtesy of AAEP

Question: I have a one-month-old foal and would like to know which dewormer would be safe to use for their age?

 Answer: Parasite control has changed dramatically over the recent few years. There was a time when treatment for intestinal parasites involved toxic chemicals that could only be administered by a stomach tube. The advent of over-the-counter “paste dewormers” provided horse owners access to safe and effective treatments they could give without veterinary assistance. Unfortunately, there is a lot of parasite resistance to most of the available compounds, so they are not as effective as they once were. It is encouraging, though, that studies show adult horses demonstrate a high degree of natural immunity against intestinal parasites, over 80%, in some populations.

Good housekeeping, daily stall cleaning and composting manure, will keep parasite populations low. Most important, is to test both the mare and foal and treat only those individuals shedding parasite eggs. Judicious use of the drugs designed to kill intestinal parasites will help control rates of infestation and limit the development of resistance in these disease-causing organisms.

Question: I adopted a mustang colt that had a cough and bloated belly. I found over 100 roundworms in his manure when I dewormed him! I need advice on a deworming schedule to control roundworms.

 Answer: Roundworms can be a problem in young horses, and yours gave clear evidence of this by his response to the deworming. Although most adult horses are naturally immune to intestinal parasites, the potential for infestation cannot be ignored. There are four compounds available over the counter, which may be helpful in controlling intestinal parasites. Unfortunately, there is significant resistance in the parasite population to most of these drugs.

With this in mind, our approach to parasite control has changed over the recent few years. A “deworming schedule” should be dictated by the presence of infestation in each individual horse. This is determined by a simple, inexpensive lab test (that your veterinarian can perform) to identify parasite eggs shed in manure. By treating only those horses with positive fecal tests, we can selectively and efficiently control parasite populations in our horses, and possibly curtail parasite resistance to our very limited choice of treatments.

Although it appears that your treatment helped your colt, a fecal sample (one fresh fecal ball is plenty) should be tested to make sure your colt is clean. An additional test should be run in six months, and repeated annually as a part of his routine vaccination and dental care. Although there are exceptions, without laboratory evidence of parasitism, “routine deworming” is not recommended.