PrintOnce upon a time, a rotational program in which every horse was dewormed with a different product every six to eight weeks protected our animals from parasites quite well. But a dewormer administered to a horse that doesn’t need it is much like a person taking an antibiotic when he doesn’t have a bacterial infection; the chance of building resistance increases as you increase the frequency of chemical exposure to a bacteria or parasite.
Many horse owners are reluctant to stop their rotational routine because they’ve never had a problem. So why should they change now? Just look at the incidence of MRSA and how the overuse of antibiotics has contributed to its emergence. Similarly, each year more and more farms across the country are diagnosed with “superworms” that are resistant to many products.
Considering that 20 percent of the equine population sheds 80 percent of the parasite eggs in any given population, it only makes sense that each horse should have his parasite burden status determined and addressed on an individual basis.
Fecal egg counts are simple tests performed on manure samples to determine a horse’s parasite burden. In mature horses strongyle eggs are the main focus. In horses less than 2 years old ascarid eggs are also counted.
It’s impossible to distinguish small versus large strongyles from a fecal count alone because their eggs look identical. It’s possible to culture the feces and differentiate the two, but this is not often done because both small and large strongyles pose a threat to the horse and high numbers need to be treated.
As always, consult with your veterinarian to help you design a program that is appropriate for your horse.
Staving Off Strongyles
In North America, five internal parasites pose the most significant health threats. In horses 2 years and older the major threats are large and small strongyles, tapeworms and bots.
Strongyles (also called bloodworms) pose the most danger and can result in poor coat, weight loss, colic and even death. They have well-developed mouth parts, including teeth, to enable them to latch on to the intestinal wall. Female strongyles lay large numbers of eggs almost constantly so a routine fecal egg count should detect them.
Due to the highly prolific nature of female strongyles, manure management is critical to decrease the number of larvae to which your horses are exposed. Strongyle eggs are passed in the manure and hatch to larvae when the temperature is between 45 and 85 degrees. Horses are infected by consuming infective stongyle larvae from grazing contaminated pastures or drinking contaminated water (such as a stream contaminated by manure).
Any horse grazing where manure is present is potentially at risk, but there are steps you can take to minimize their exposure. Decreasing the parasite burden within the horse will decrease its “pasture contamination potential” because fewer worms harbored translates into fewer eggs passed into the environment.
Removing manure from pastures on a regular basis is one of the most effective management treatments available. The frequency with which this needs to be done varies with temperature. The eggs passed in manure do not infect horses; rather the eggs must hatch and then progress through three larval stages before they are consumed by horses in order for them to establish an infection.
