Sheep dewormer resistance growing problem
Internal parasites, commonly known as worms, are a growing problem in sheep flocks around the world.
By Kimberly Fillmore
Sheep with high worm burdens may experience health problems such as slow growth, diarrhea and even death. One particular parasite, the barber pole worm, even sucks blood, causing the animals to become anemic as they lose red blood cells.
These parasites are easily passed from sheep to sheep throughout an entire flock. In an infected animal, adult worms live in the digestive tract and shed their eggs in the feces. Once these eggs mature, they hatch into larvae on the pasture and infect other sheep that pick them up while grazing.
"A female barber pole worm may lay up to 5000 eggs per day," explains Dr. Fabienne Uehlinger, a large animal clinician at the Western College of Veterinarian Medicine (WCVM). "If there are 500 female worms in a sheep host and there are 200 infected sheep in a flock, then a flock may contaminate a pasture with 500 million eggs per day."
Although producers can use anthelmintics, also known as dewormers, to kill these intestinal worms, these drugs are now less effective as the worms adapt to them, developing a trait known as anthelmintic resistance. That's a major concern to sheep farmers as they cope with unhealthy flocks while paying for drugs that aren't effectively killing the parasites.
"The reason anthelmintic resistance may be a big issue is that sheep are susceptible to gastrointestinal nematodes (worms), and particularly the barberpole worm can have (fatal) detrimental production impacts," explains Uehlinger.
Uehlinger is heading a research team at the WCVM that's investigating anthelmintic resistance in Saskatchewan sheep flocks. The researchers have two objectives: to determine whether on-farm deworming practices are controlling the parasites and to test the effectiveness of specific dewormer products.
The first part of the investigation involves an on-farm deworming assessment aimed at informing sheep producers whether deworming practices are working on their farms. After deworming the sheep using their customary product and technique, the producers send fecal samples to the WCVM lab for analysis to determine the parasite load.
The second part of the research assesses two different anthelmintic products, Ivomec and Safeguard – products that are commonly used by sheep producers. The researchers travel to sheep farms around Saskatchewan to deworm animals and collect fecal samples. On each farm the sheep are randomly placed into one of three groups: Ivomec, Safeguard and a control group which receives no drug.
Fecal samples are collected on the first visit and then again two weeks later so that fecal egg counts can determine the effectiveness of the drugs. Ideally, anthelmintics should kill more than 95 per cent of the parasites present at the time of deworming.
Early results indicate that egg counts after deworming are not being reduced by 95 per cent, and the researchers believe anthelmintic resistance is a major player in these results – that's bad news for Saskatchewan sheep producers.
"Up until a few years ago, anthelmintics were able to control these worms and, therefore, gastrointestinal nematodes (worms) were not necessarily regarded as a significant problem," says Uehlinger. "However, with increasing resistance, we'll see increased disease and death due to internal parasites in sheep. It may be necessary to find treatment options in the future other than traditional dewormer drugs."
Kim Fillmore is part of the WCVM Class of 2018. She is originally from Westbridge, B.C. Kim's story is part of a series of articles written by WCVM summer research students.
These parasites are easily passed from sheep to sheep throughout an entire flock. In an infected animal, adult worms live in the digestive tract and shed their eggs in the feces. Once these eggs mature, they hatch into larvae on the pasture and infect other sheep that pick them up while grazing.
"A female barber pole worm may lay up to 5000 eggs per day," explains Dr. Fabienne Uehlinger, a large animal clinician at the Western College of Veterinarian Medicine (WCVM). "If there are 500 female worms in a sheep host and there are 200 infected sheep in a flock, then a flock may contaminate a pasture with 500 million eggs per day."
Although producers can use anthelmintics, also known as dewormers, to kill these intestinal worms, these drugs are now less effective as the worms adapt to them, developing a trait known as anthelmintic resistance. That's a major concern to sheep farmers as they cope with unhealthy flocks while paying for drugs that aren't effectively killing the parasites.
"The reason anthelmintic resistance may be a big issue is that sheep are susceptible to gastrointestinal nematodes (worms), and particularly the barberpole worm can have (fatal) detrimental production impacts," explains Uehlinger.
Uehlinger is heading a research team at the WCVM that's investigating anthelmintic resistance in Saskatchewan sheep flocks. The researchers have two objectives: to determine whether on-farm deworming practices are controlling the parasites and to test the effectiveness of specific dewormer products.
The first part of the investigation involves an on-farm deworming assessment aimed at informing sheep producers whether deworming practices are working on their farms. After deworming the sheep using their customary product and technique, the producers send fecal samples to the WCVM lab for analysis to determine the parasite load.
The second part of the research assesses two different anthelmintic products, Ivomec and Safeguard – products that are commonly used by sheep producers. The researchers travel to sheep farms around Saskatchewan to deworm animals and collect fecal samples. On each farm the sheep are randomly placed into one of three groups: Ivomec, Safeguard and a control group which receives no drug.
Fecal samples are collected on the first visit and then again two weeks later so that fecal egg counts can determine the effectiveness of the drugs. Ideally, anthelmintics should kill more than 95 per cent of the parasites present at the time of deworming.
Early results indicate that egg counts after deworming are not being reduced by 95 per cent, and the researchers believe anthelmintic resistance is a major player in these results – that's bad news for Saskatchewan sheep producers.
"Up until a few years ago, anthelmintics were able to control these worms and, therefore, gastrointestinal nematodes (worms) were not necessarily regarded as a significant problem," says Uehlinger. "However, with increasing resistance, we'll see increased disease and death due to internal parasites in sheep. It may be necessary to find treatment options in the future other than traditional dewormer drugs."
Kim Fillmore is part of the WCVM Class of 2018. She is originally from Westbridge, B.C. Kim's story is part of a series of articles written by WCVM summer research students.