This month:

Ascarids, or roundworms, are typically only a problem for foals and young horses, since equids generally develop a form of immunity around the age of two. However, they're still a significant health hazard and care must be taken in their control to avoid an infestation that could prove deadly.

Ascarid (Parascaris equorum) eggs have a sticky protein coating and thick shell, so not only are they hardy (remaining viable for up to a decade), they stick to just about anything, from the walls of a stall to the dam's hair coat. Disinfectants and even steam-cleaning have been shown ineffective in killing ascarid eggs; the best defense is to remove manure frequently, before eggs incubate and become infective.

Once eggs are passed with manure into the environment, it only takes a few weeks for larvae to incubate inside the shell; once the larvae are formed, the eggs are infective and once ingested by the grazing foal or young horse, continue on their lifecycle. Hatching in the small intestine, the parasites travel through a horse's liver, bloodstream, and lungs, eventually returning to the small intestine where they mature and begin to produce eggs. A single female ascarid can lay hundreds of thousands of eggs each day.

While roundworms aren't a serious issue for adult horses, they can be problematic in foals, weanlings, and yearlings. Signs of an ascarid infestation include malnutrition despite a good diet, and signs of respiratory disease (including coughing, nasal discharge, and fever). Severe colic might also occur, from a mass of tangled ascarids blocking the small intestine. This is especially a concern following anthelmintic deworming for ascarids, because the dead worms can collect in the intestine and become impassable; it's important to watch foals for any sign of colic within the first 24-48 hours after deworming and to act quickly if symptoms arise.

It's difficult if not impossible to detect immature P. equorum passing through a horse, but a fecal egg count is able to detect infestations of adult, egg-laying ascarids. However, your best management for ascarids lies in taking steps to prevent infestation: