Internal parasites are silent killers. They can cause extensive internal damage, and you may not even realise your animals are heavily infected. At the very least, parasites can lower resistance, rob the horse of valuable nutrients, and cause gastrointestinal irritation and unthriftiness. At their worst, they can lead to colic, intestinal ruptures, and death.

There are more than 150 internal parasites that afflict horses, including several major species. Among the most common and troublesome are:

  • Large strongyles (bloodworms)
  • Small strongyles
  • Ascarids (roundworms)
  • Pinworms
  • Bots
  • Tapeworms
  • Threadworms
  • Lungworms

Any or all of these parasites can be present in the horse at one time, but they may be at different stages in their life cycles. This will influence the deworming program needed to combat them. Also, keep in mind that some species can lay more than 200,000 eggs a day, so parasite loads can escalate quickly.

Signs of infestation might include:

  • Dull, rough haircoat
  • Lethargy or decreased stamina
  • Weight loss
  • Coughing and/or nasal discharge
  • Tail rubbing and hair loss
  • Resistance to the bit due to mouth lesions
  • Colic
  • Summer sores
  • Depression
  • Loss of appetite
  • Unthriftiness or loss of condition
  • Diarrhea