“I have heard NEVER worm a foal before 5 months of age but so many are worming many times before that age. What is the correct worming protocol for a baby?”

Jennifer L. Wright, DVM

That is a great question, Debbie, because the parasite protocol for foals differs greatly from that recommended for adult horses for 2 primary reasons:  1) the foal’s immune system needs to be allowed to safely mature and develop crucial antibodies against parasites in a controlled manner, and 2) the targeted group of parasites differs from that of adult horses.  Ascarids (roundworms), Strongyloides westerii and small strongyles are the targeted parasites for foals, whereas small strongyles, tapeworms, bots and pinworms are the targeted parasites for adult horses.  Foals are not selected for deworming treatment solely based on Fecal Egg Counts (FEC), as recommended in adult horses.  Instead, the following considerations should be made:

Foal Grazing

Foal Grazing

  • It is recommended to deworm the mare immediately prior to or immediately post foaling with Ivermectin or Quest to prevent the transmission of Strongyloides westerii to the foal through the milk.
  • During the first year of life, foals should receive a minimum of 4 anthelmintic (deworming) treatments:

o    Deworming #1 should be administered at about 2-3 months of age with a benzimidazole drug (i.e. Panacur) to target roundworms.

o    Deworming #2 should be administered just before weaning (about 6 months of age).  A FEC is recommended at this time to determine whether the parasite burden is primarily roundworms or small strongyles in order to determine the proper deworming treatment choice.

o    Deworming #3 should be administered at 9 months of age, and the treatment should target small strongyles.

o    Deworming #4 should be administered at 12 months of age, and the treatment should target small strongyles and tapeworms.

  • Recently weaned foals should be turned out onto the cleanest pastures with the lowest parasite burdens.
  • Perform a yearly Fecal Egg Count Reduction Test (FECRT) on yearlings and two-year olds to evaluate the efficacy of the deworming drugs that have been administered against roundworms and small strongyles.
  • Yearlings and two-year olds should continue to be treated as “high shedders,” and receive three to four treatments with appropriate deworming products.
Roundworms in Manure

Roundworms in Manure

The take-home message is that deworming a foal is very different from deworming an adult horse, and this strategy is designed to effectively control dangerous parasites while decreasing the risk of developing parasite resistance to the deworming drugs employed.  Similar to adult horse parasite control programs, each foal’s parasite control program may be tailored to address specific farm conditions and the individual health status of the foal.  It may seem like an overwhelming task to develop a safe and effective parasite co