One of the most crucial aspects of your horse's health is the control of internal parasites. Parasites are one of the most costly and harmful afflictionsof the horse. Infestations can lead to colic, anemia, diarrhea, poor growth or weight loss, reduced stamina and decreased performance. Every farm, whether it has one horse or one hundred, should have an effective parasite control program in place. The goal of this programshould be to decrease the transmission of parasites between horses and the environment. 

• The program should be aimed at controlling:
• Large and small strongyles in all horses
• Ascarids in yearlings and younger horses
• Bots in all horses after the first hard freeze.
• And other parasites that may be a problem in a particular area or with individual animals.

There are four aspects to a good control program: 1) The choice of dewormer, 2) The administration schedule, 3) Non dewormer management practices i.e. Environmental controls, and 4) the monitoring of results so that the program can be monitored.

Choice of Dewormer

There are five major chemical classes of wormers: (1) avermectins (2) organophosphate  (3) tetrahydropyrimidines (4) benzimidazole (5) and piperazine. These drugs all have similar  efficiencies and resistance and it is often recommended that a wormer from a different class be used on a rotating basis.  Recent studies have shown that there is little difference between a  rotational program and one that uses the same dewormer for an extended period of time.  Eqvalan and Quest contain ivermectin and moxdectin respectively and are considered to be avermectins. The Mira all in one, Mira paste wormer and Safeguard are from the benzimidazole class. The Mira all in one also falls into the organophosphate class because it contains Trichlorfon. Piperazine can be purchased as a soluble powder and mixed into the feed or water. As long as the product remains effective you should develop a program, with the help of your vet, that best suits your farm.

Administration Schedule

There are three different types of administration schedules used in controlling parasites. Most commonly used is an interval-deworming program that involves treatingevery two months. On some farms where there is a particularly great problem, a non avermectin dewormer can be used once a month with an avermectin every two months. It should not be necessary in most cases to treat every month.

A seasonal deworming program, which involves treating at critical times of the year, can be used for mature horses but is not recommended for horses less than one year of age. Seasonal programs  involve treatment in the spring before grazing begins in the pasture, in the middle of the summer and in the fall followinga hard freeze. This type of program is not effectivefor young horse because ascarid, strongyle and bot control are necessary in young horses at all times. It is also important not to use a method on young animals that would cause a sudden parasite kill. Slow kill dewormers are less likely to cause complications such as impaction colic and stress on the animal.

Continual deworming programs involve the continual feeding of low amounts of deworming  medications. This method may prove to be of questionable value however, as many small strongyles develop a resistance to dewormers used in this manner.

Consult you veterinarian to be sure you are following the proper program for your farm.

Environmental Control

Administering a dewormer should be only part of a good parasite control program. Management practices should also be implemented with the goal of minimizing the amount of fecally contaminated feed and water the horses ingest.

There are a number of ways in which this can be accomplished:

1. Minimize the consumption of feed from the ground.
2. Remove manure from stables, paddocks and small pastures frequently.
3. Let manure compost for a year before spreading it on horse pasture. This ensures that the heat  of fermentation has killed all parasite eggs and larvae.
4. Do not allow pastures to become overgrazed. If horses are forced to graze forage close to the  ground and around fecally contaminated areas ingestion of eggs and larvae is more likely.
5. Harrow pasture to break up fecal matter and expose larvae to heat from the sun. Do not harrow in damp weather as this only disperses the infective larvae over a greater area and will not  kill them.
6. Keeping horses off pasture for 4–12 months ensures that parasite larvae are dead. Cooler,  damper climates may require a longer time period as parasite eggs may survive even very  cold winters.
7. Keep new horses or horses returning to the farm isolated for 7–14 days, treat them with a  non-benzimidazole wormer, and vaccinate them if necessary. Most infectious diseases are  contagious 7–14 days before clinical signs are observed. Isolating new animals will help to  ensure the good health status of your herd.