‘Weird and wonderful therapies’ are available, but none are proven effective, say experts
Parasites are like the plague for sheep producers.
“Parasites are the No. 1 problem for sheep producers globally,” said John Gilleard, a parasitologist at the University of Calgary’s faculty of veterinary medicine.
“That and foot rot are the two diseases they are worried about most.”
No recent surveillance has been conducted in Western Canada, so he and researcher Michael Levy took a look on farms across the province. They found high levels of parasites and increasing resistance to common treatments such as ivermectin and fenbendazole, an active ingredient in Safe-Guard.
Another project has been approved to continue the work, which focuses on identifying the most troublesome parasites and gathering evidence of resistance to parasiticides.
Haemonchus contortus is one of the most serious parasites attacking sheep. It was originally a tropical parasite and spread with livestock movement across the world in the last 200 years.
It has adapted and thrived in cold climates and is passed onto pasture via feces. It feeds on blood and can cause diarrhea and anemia, which may kill lambs.
“It is the growing lambs where it has a major impact. Typically around weaning is when you see the biggest problems,” Gilleard said.
“Sheep coming off pasture at the end of the grazing season are going to have parasite burdens, and they are going to have a negative impact on growth rates, and there is a risk of clinical disease with the parasites.”
The parasite can be difficult to treat because not many products are ap-proved for sheep. Ivermectin works and has been used extensively. Fenbenzole is not approved, but it has been used with a veterinary prescription.
Australia, Europe and the southern United States have heavily used these drugs where resistance problems become significant.
“Producers are really struggling in terms of control,” he said.
“Treating them with drugs will only be effective if the drugs are actually going to do their job.”
Canadian producers need to work with their veterinarians to get a management structure in place and practice pasture management. No alternative treatments are available.
“There is a huge variety of weird and wonderful therapies, and none of them really have much objective or empirical evidence to show they are any good,” Gilleard said.
He suggested a strategy that treats only the most infected animals in the flock. Most of the parasites are probably spread by a small number of ewes.
Fecal samples should be collected to see which parasites are present.
Ewes can be condition scored, and those with low scores should be treated. Underweight lambs should be treated.
Continuous grazing, in which sheep return year after year to the same pasture, sets up the animals for constant parasite problems.
Ideally, sheep that graze a pasture one year should not be back the following year.
“(Parasites) won’t survive on that pasture for more than a year. It should be clean two years later,” he said.
Most livestock can pick up parasites from pastures, but horses, cattle and sheep are infected by different kinds of worms. As a result, sheep could go on a pasture on which cattle had grazed the previous year.
“By and large, they don’t share the same species with relative exceptions,” he said.
“The more important species are not shared, so alternating sheep and cattle is a good method of control.”