Worms are parasites that live and grow in the digestive tract. Horses pick them up mainly through grazing and once ingested, can cause a myriad of health problems including colic. To prevent parasitic problems in horses, a good deworming program is essential.
Rotating Dewormers Thought to Provide Broad Spectrum Coverage
According to Julie Goodnight, spokesperson for Certified Horsemanship Association, in “Rotating Horse Worming” on www.cha-ahse.org, there are 4 major types of worms that infect horses—pinworms, ascarids, strongyles and bots. All affect the digestive tract in some way, but large strongyles are the worst of the group, often leading to complications that can result in sudden death. There are a variety of products on the market to combat internal parasites, but according to Goodnight, rotating them may provide the best coverage.
Some parasites are only active at certain times of year, and according to Goodnight, “each type of dewormer has efficacy against varying parasites and at different stages of the parasite’s life cycle. So rotating dewormers gives horses better coverage against the four major types of internal parasites that infect horses.” Since current guidelines differ as to the best season to deworm, Goodyear thinks it makes sense to keep a horse on a year round schedule. Deworming once every 2 months with a dewormer that is appropriate for the parasites and phases of life provides safe coverage.
Does Rotating Help to Avoid Chemical Immunity?
It has been suggested that rotating deworming products can prevent parasite resistance to the chemicals used in dewormers. According to Goodnight, resistance was always a concern prior to the advent of the chemical dewormer Ivermectin. While Ivermectin promised to eliminate the threat of immunity, many believe that overuse will lead to resistant strains of parasites, and that rotating dewormers can help prevent such an occurrence.
Dr. Harold C Mckenzie of the Marion Dupont Scott Equine Medical Center at Virginia Tech presented an informational presentation on January 13, 2009 entitled “Emerging Issues in Equine Parasitic Management”. According to Dr. McKenzie, immunity in parasites is evolving on a fast scale. Parasites once thought controlled are reemerging and parasites that once were thought to cause only minor problems are now on the rise. In his opinion, rotational deworming alone will not solve the problem.
Management is the Key
According to McKenzie, better management practices that include the use of Parasitic dewormers on a less frequent basis is key to helping avoid the problem of parasitic immunity. Dewormers should be used most often on horses that need to be treated, meaning those with higher counts of the parasites. This involves monitoring fecal egg counts and adjusting medications accordingly. In addition to these steps, McKenzie recommends the following to aid in controlling internal parasites.
- Do not overstock pastures
- Rotate pastures
- Pick up manure from paddocks
- Do not allow overgrazing
- Avoid feeding from the ground
- Compost manure for at least one year
- Graze pastures with other livestock including cattle and sheep
Rotating dewormers is a good idea for better parasite control, but rotating alone is no longer universally accepted as a means to controlling the problem of internal equine parasites. Instead, a broader approach is needed, one that will require more investment of time and resources, but will ensure that parasites are controlled well into the future.
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