Large Roundworms (ascarids)Photo kindly provided by University of Liverpool Diagnosteq LabAscarids, (also known as roundworms) are parasites which are mainly a problem to foals. However, small numbers can also be carried by adults.
The adult worms are very large and can be up to 40cm in length. Once the larvae of this parasite are swallowed, they pass through the gut wall, via the liver to the lungs. Heavy infestations can cause coughing as the larvae travel through the lungs.
Adult worms can cause intestinal impaction. They pose a considerable threat to young horses and their developing immune systems, and they have to potential to kill by triggering colic. Even if a young horse escapes colic, a heavy ascarid burdened young horse will appear depressed and its normal growth will be affected.
The most common ascarid to infect horses is Parascaris equorum.The eggs laid by the large females pass out into pasture protected by a tough shell which equips them well for survival. They can withstand drying conditions and even freezing; waiting for that moment when a passing horse ingests them with grass.
Large Roundworms - treatment options and resistance
| Fenbendazole | Pyrantel | Ivermectin | Moxidectin | Praziquantel | ||
|---|---|---|---|---|---|---|
| Parascaris spp. | Some resistance now reported FECRT should be performed | Some resistance now reported FECRT should be performed | Resistance is common Should only be used with FECRT | Resistance is common Should only be used with FECRT | Not indicated | |
Source: Canter Guidelines
Remains effective for indicated use
Resistance emerging or suspected
Some resistance reported – FECRT should be performed
Resistance common – should only be used with supportive FECRT results
Not indicated for use for treatment
