Controlling internal parasites in your horses should be a routine management strategy that all horse owners are familiar with. A tool that is commonly used to determine the effectiveness of that treatment is known as a Fecal Egg Count. This procedure will let you know the number of parasite eggs being shed into the environment through your horse’s manure. Though the summer is the time when parasites are more of a problem, knowing what your horse’s egg count is at any time of the year will provide you with valuable information. Fecal egg counts can monitor pasture contaminations, monitor efficacy of anthelmintics and detect resistance to those anthelmintics. Just like everything however, fecal egg counts have their limitations, there can be animal to animal variation in these tests and you must evaluate the results in context with several variables. Like the time of year, since there can be some seasonal variations, the treatment history of animal, and the animal’s health condition. Also, if the test doesn’t detect parasite eggs, that does not mean the animal is free of GI parasites, they could just have larvae that are not shedding at that time.
You should consider running fecal egg counts before treatment with anthelmintics and again 10-14 days after treatment. Compare the FEC and you want to see a 90-95% reduction, if this level is not obtained then you might have some resistance. Most horses have a pretty decent immunity to parasites. One of the more common parasites is the small strongyle and according to an extension publication by Penn State, 40-60% of adult horses tend to be low shedders of small stronglyles and 10 -30% are high shedders. Meaning that typically 80% of eggs come from 20% of the horses on the farm. With this in mind, the results of a fecal egg count can tell you if your horse is a low or high shedder and research has shown that adult horses typically shed the same number of eggs throughout their lifetime. Meaning, if your horse is a high shedder they will stay a high shedder so stay on top of deworming them.
Some people think that they don’t need to worry about parasites in the winter. In actuality eggs can hatch at 42 degrees fahrenheit and in NC that can be well into the winter months. Freezing will stop the hatching of eggs and the development of larvae but it does not kill either. In order to kill them you have to compost the manure and allow it to reach a temperature of 104 degrees fahrenheit. The deworming strategy promoted today is to use anthelmintics that have proven efficacy and are administered at the appropriate time of the year based on the parasite burdens of each horse individually. Consider focusing deworming treatments during times of peak transmission when the number of non-resistant parasites are the highest in the pasture, this is normally spring through fall. If at the very least you consider deworming the high shedders only, the number of eggs being shed into the environment will significantly be reduced. Also remember, young horses, under 3 years of age require more frequent deworming times as well as pregnant or nursing mares. These two groups are more susceptible to parasites because of their lower immune system.
How do horses come in contact with parasite eggs? Well think about the way a horse grazes, on the ground and they typically bite as low as they can on a piece of grass so they can get as much as they can in each bite. What else is on the ground, yes parasites. Parasites from their own or other horse’s manure, deer, if you have cattle or small ruminants then parasites from their manure as well. Most of the parasites can be found on the ground and as high as 3 inches up the grass. This needs to be taken into consideration when making a rotational grazing management plan, don’t let your horses graze down their pasture too much and when feeding hay, don’t feed hay on the ground.
For help with performing a fecal egg count on your horses, contact your local extension agent.