Dear HH: What do you suggest for deworming horse herds that are out on 100 acre pasture?
Joyce Harman, DVM, MRCVS of Harmany Equine Clinic , responds:
Horses out on large acreage often are much less exposed to parasites than horses in more confined areas. They can move around with the seasons, and rarely need to graze near their manure areas, so the larvae are not eaten. If the numbers of horses are small or the horses are handled regularly, take fecal samples from everyone and see what you have. You may find one or two that shed eggs; those may do well with a deworming treatment. Those that are negative or have low parasite counts do not need anything. If there are many horses or they are not handled much, take a sample of fecals (go into the pasture and select 5-10 fresh looking piles), and check those. It will give you a sample of what is going on, and an idea if you need to consider a program for all the horses. If a horse or two does not look as healthy, try to sample their manure. Natural dewormers can be used, but if access is limited, a single dose of a chemical dewormer may be more realistic. Natural dewormers usually have to be given over several weeks.