Sheep and goats commonly contract a deadly, blood-sucking parasite, Haemonchus contortus (H. contortus).
Also known as the barber pole worm for its red-striped appearance, it resides in the abomasum, or fourth stomach.
Blood loss is the most important effect of this parasite. Individual worms can consume 0.05 millilitres of blood a day.
Given that thousands of worms can live in an animal, this repeated blood loss is substantial, even over short periods of time. Anemia develops, which is a reduced number of red blood cells in the blood.
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Affected animals have pale or white gums and conjunctiva, which is the area inside the lower eyelid. These tissues should be bright pink to red.
Bottlejaw, which is edema of the tissues under the neck and jaw, develops because fluid leaks from the blood.
The worms suck red blood cells and protein, so the reduced protein allows the water components of blood to leak out. Gravity collects this fluid in the lower parts of the body such as the jaw, neck and belly.
As with any anemia, clinical signs include weakness, shortness of breath, inability to exercise and sudden death. Slow weight gain and poor body condition are other general signs of parasitism.
A tentative diagnosis can be reached based on these clinical signs. Testing feces for worm eggs or performing autopsies on deceased animals can confirm infection.
The most severe disease occurs in growing lambs and kids, although young adults are also affected. Mature adults develop immunity in most circumstances.
The life cycle of this parasite is simple. Adult worms within the stomach pass eggs in the feces. These hatch and go through several larval stages in the environment. They are ex-tremely resistant to drying out by the time they reach the infective larval stage.
Grazing sheep and goats ingest the worm, which enters the stomach lining. It can undergo a hibernation stage in winter, where it keeps dormant until the weather improves. Otherwise, it matures into adults and produces more eggs.
Like most parasites, the barber pole worm thrives in warm, wet conditions.
The best way to control it is to interrupt its life cycle.
Resistance to dewormer medications is a growing problem, which means strategic treatment of the most severely infected animal is better than deworming the entire group.
One-third of animals carry most of the worms.
The lower eyelid can be examined for anemia using the Famacha system, while body condition scoring can identify those most severely infected. These animals can then be treated before winter confinement and released onto new pastures to reduce the number of worms in the new environments.
Although it may seem counterintuitive, a small number of non-resistant parasites in the herd or flock dilutes the resistant parasites to maintain future susceptibility to dewormers.
Leaving the least-affected animals untreated will preserve these non-resistant parasites.
Rotational grazing can also help control this parasite. Sheep and goats should be moved to pastures that have not been grazed in at least three months, or onto pastures previously used by cattle or horses.
Sheep and goats that have the barber pole worm usually also have other worm species lower in the intestines. These may cause less severe disease, but control is important from a productivity perspective.
Parasite control programs should be given high priority, considering the severe loss of production attributed to parasites such as the barber pole worm.
Some veterinarians go so far as to advocate planning other routine care procedures such as vaccination and hoof trimming around the deworming schedule.
