This decision should be made in conjunction with post-treatment fecal exams and veterinary consultation. Foals under one year of age and very old horses. Foals under one year of age are susceptible to heavy parasite infestation. We recommend deworming at one month of age, and then every month until weaning. After weaning, deworm every six weeks until 12 months of age, then every eight weeks thereafter.
Threadworms can also be a problem for foals under six months of age.
They are not common in the older horse. Older horses, in their late teens, often have a weaker immune state than adult horses in their prime and are more susceptible to parasites. Older horses may require deworming every six weeks, especially if they experience any of the digestive tract problems that often accompany old age. Horses that share a large pasture with a relatively unchanging population. If a small, unchanging herd is on a large pasture and has been on a six times a year deworming program for a year or two and fecal egg counts are low, it may be practical to decrease the deworming frequency to four times per year.