Parasitism is the most common disease of horses today. It is also one of the most costly and damaging diseases which is omnipresent in the equine population. Thirty years ago this costly damage had visible, physical, and measurable signs, such as: bloody diarrhea, sunken flanks, dull, rough hair-coat, verminous pneumonia, intestinal rupture and arterial aneurysm.
Today, this costly damage is less visible, physical, and measurable, and is reflected by conditions such as: depressed or delayed growth, unthriftiness, missed conception and poor performance. Very different signs and conditions, yet still just as serious.
As is the case with most animal species, internal parasites are particularly damaging to young horses; however, even in the older horse there is a constant battle to control parasites.
The major parasites of horses include: ascarids, pinworms, small strongyles, large strongyles and bots.