Parasites
All horses and ponies have a parasite burden, and therefore treatment is periodically needed throughout the horse or pony’s life. Some steps to reduce parasite infection include regularly removing droppings from the horse’s stall, shed or field; breaking up droppings in fields by harrowing or disking; minimizing crowding in fields; periodically leaving a field empty for several weeks; or placing animals other than horses on the field for a period of time. If botflies are active, fly spray may repel insects, but needs frequent reapplication to remain effective. A small pumice stone or dull knife may be carefully used to scrape off any bot eggs that are stuck on the horse. (Bot eggs are yellow and roughly the size of a grain of sand, they are clearly visible on dark hair, harder to spot on white hair.)
However, worms cannot be completely eliminated. Therefore, most modern horse owners commonly give anthelmintic drugs (wormers) to their horses to reduce these parasites.
Methods of Worming
There are 2 common methods of worming. Purge wormers that kill parasites with a single strong dose, are given periodically, usually every 8-12 weeks, depending on local conditions and veterinary recommendations. Continuous wormers, also known as "daily" wormers, are given in the horse’s feed each day, in small doses, and kill worms as they infect the horse. Neither of these methods is perfect; purge wormers are effective for rapidly killing all parasites, but are gone from the horses’ body in a few days, and then the horse may start to be re-infected. Continuous wormers are a mild low dose and may be easier on the horse, but may not be effective in quickly killing worms in a heavily-infected horse, and may contribute to drug resistance. Neither type will kill all types of worms, so horses normally require a purge worming with a different drug on a rotating basis, at least 2 or 3 times per year.
Many horse owners also rotate between the different chemical classes of wormers to combat the tendency of parasites to develop resistance to a given class of drugs. (If a treatment doesn’t kill at least 95% of a worm species, that species is classed as ’resistant’ to the drug.) Another way of combating drug resistance is to worm less frequently, by having manure samples tested for the presence of parasite eggs and then worming only when the count gets high enough, and with a wormer specific for the type of worm eggs found. However, this method is not entirely reliable, as the parasite load varies somewhat with the seasons, and some parasites (such as bots) may not show up in a fecal egg count at all.
Wormers come in several forms, including pastes, gels, powders, and granules or pellets. Powders and granules normally come in single-dose packaging, and the wormer is normally mixed in with the horse’s feed. Pastes and gels normally come in a plastic syringe which is inserted in the side of the horse’s mouth and used to squirt the wormer onto the back of the horse’s tongue.
Risks of worming
Modern anthelmintics are quite effective against worms. However, if a horse is heavily infested with parasites, wormers must be given carefully. A horses’ body may be overwhelmed by the toxins released by a heavy load of dead worms after worming with a powerful drug. There have been documented cases of horses, particularly if also undernourished, ill, or otherwise weakened, to become sick or even die. Thus, a veterinarian may recommend worming with a mild class of drugs, such as Panacur, or a low-dose daily wormer for the first month or so, and then follow with periodic purge wormer treatments.
Types of parasites found in equines:
- Ascarids, also known as roundworms
- Pinworms, sometimes known as seatworms
- Tapeworms
- Strongyles - large and small, sometimes known as Redworm.
- Bots - a fly larvae - bot eggs are laid on a horse’s coat, and when accidentally ingested through the horse licking its coat, the larvae hatch in the tongue, migrate down the esophagus and mature in the stomach.
Ringworm in horses is not actually a worm but a contagious fungal skin disease and is normally treated using an anti-fungal wash.
There are several different brands of wormer, using different types of active chemical - which in turn kill different types of parasites. It is sometimes necessary to use a specific wormer at a certain time of year, depending on the life cycle of the parasites involved. Many horse owners rotate wormers during the year, using different brands or formulations with different active chemicals, to combat drug-resistant parasites.
