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The horse ingests infective larvae, which then penetrate the intestinal wall and migrate along the blood vessels of the abdominal cavity of the horse. The larvae continue to develop until they become mature adults. The adult worms return to the cecum and colon of infected horses, where they lay eggs. The eggs are passed in the feces and the cycle starts over again.
The migration of the immature larval stages of large strongyles through the blood vessels can cause inflammation and blood clots (thrombosis), which can limit blood supply to the intestinal tract. The resulting thromboembolic colic often results in death of the horse. Other clinical signs of large strongyles include anemia, loss of appetite, weakness, emaciation and diarrhea.
Horses at greatest risk:
Large strongyles are now considered rare, especially in well-cared-for horse populations, thanks to effective dewormers. Horses that have not been – or poorly – dewormed are at greatest risk for large strongyles.
Adults are found in the small intestine and eggs are passed in the feces of infected animals, where they can live and remain infective for years in stalls, paddocks and pastures. When eggs are ingested the larvae hatch and migrate through the walls of the small intestine to the liver, and then to the lungs via the heart and pulmonary organs. The larvae invade the lungs and are coughed up and swallowed where they pass into the intestinal tract and become adults in the small intestine, where the cycle starts over.
Signs of respiratory infection include cough, nasal discharge and low-grade fever. Signs of intestinal disease include weight loss, poor condition, loss of energy, pot belly, impaction colic and bowel rupture, which can be fatal.
Foals and weanlings. Adult horses develop some immunity unless infestation is extreme and unchecked.
BIOSECURITY NOTE: Eggs can live and remain infective for years in stalls, paddocks and pastures increasing the potential for spreading ascarid infection between horses and even re-infecting the original host animal. Attention should be paid to managing and cleaning premises where foals have been shedding large numbers of ascarid eggs and contaminating stalls and surfaces.
Adult worms are found in the cecum and colon of infected horses. The adults lay eggs which are passed in the feces. Eggs hatch and the larvae mature to the infective L3 stage. Third stage larvae are ingested on pasture and invade the mucosa of the large intestine. At this time the maturation of the larvae may hibernate – or encyst – for prolonged periods of time. As many as 90% of the larvae may become encysted in this manner and remain in this stage of development for 4 months or up to 3 years. The climate dictates when hibernation occurs and when the larvae will emerge and continue toward maturation.
Primary disease threat lies in mass emergence from the encysted stage, which can lead to weight loss, diarrhea, colic, edema, fever, dull hair coat, decreased performance and even death.
Considered a major parasite risk in adult horses. Young horses and immunocompromised horses are also susceptible.
Infective eggs are ingested on pasture and the larvae hatch in the small intestine. After further maturation they migrate to the cecum/colon of the horse. Adult female pinworms migrate up the rectum and out the anus to cement masses of eggs on the perineal area. The egg masses cause irritation, and environmental contamination occurs when horses rub the irritated area against posts and barn walls.
Most common clinical sign is tail rubbing due to skin irritation in the perineal area.
Young horses less than 18 months of age. Most horses develop immunity as they age.
Consult your veterinarian for assistance in the diagnosis, treatment and control of parasitism.
Controls large strongyles, small strongyles, pinworms and ascarids.
Feed and deworm in a single step with palatable alfalfa-based pellets.
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