Veterinarians have been doing fewer fecal tests as deworming products become more reliable, but that may change as worms grow increasingly resistant to macrocytic lactones (avermectins).
Parasitologists talk about a fecal egg count reduction test, which is measured as the percentage drop in egg counts two weeks after treatment with a dewormer. Any amount less than 90 percent is considered to be evidence of resistance building up.
Most of the previous evidence for resistance was found in the more temperate areas of the United States, but recent work by pharmaceutical companies and an independent researcher found similar results in Canada.
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The research has found parasite reduction of 55 to 85 percent in multiple replicate pastures, which clearly shows that internal parasite resistance is still a problem in Canada, despite our colder climate, which puts parasite transmission in suspended animation.
Alternating classes of dewormers and more strategic deworming are two possible ways to decrease resistance. Stacking classes of dewormers is another option.
Herd veterinarians are in the best position to offer advice on deworming based on results of fecal sampling.
One fecal flotation test on a large herd may not provide adequate evidence, but several will. It’s said that 20 fresh individual samples on even the largest herd give a representative sample and will catch high egg shedders.
The samples are easy to collect, even at pasture, but they must be fresh and analyzed quickly or shipped at refrigeration temperature with ice packs.
Parasite eggs can be easily recognized, and some species, such as Nematodirus, trichuris, tapeworms, round worms and coccidian, can be identified.
However, determining overall worm burden is most important.
Lice are still a major problem in Canada, but they are showing no resistance to the avermectins.
It probably makes sense to stack classes of dewormers, especially if fecal results support this and in the fall when lice control is needed.
The benzimidazoles have been around a long time.
Fenbendazole (Safeguard) is effective on worms, including the difficult and significant Nematodirus and lungworms. It comes in various forms, including a drench, pellets and a concentrated feed additive.
Studies achieved 99.9 percent effectiveness in trials using both Safeguard and avermectins.
Fenbendazole is not effective against the inhibited L3 larval stages of some parasitic forms. It is really a contact dewormer, which means it wipes out all the other stages, including the adults.
In the case of heavy worm burdens, the L3s then become adults and eggs are shed again.
Deworming two to three times a month apart will reduce the worm count to close to zero in cases of heavy worm burdens. This is rarely necessary, but it stresses the need for fecal monitoring to strategically provide the most benefit to an individual herd.
As well, cattle are continually picking up parasites while on pasture.
Veterinarians can prescribe fenbendazole for use in salt and minerals if cattle cannot be easily accessed, such as at pasture. They would be consumed over periods up to a week or in feed consumed over one to three days.
A handy hook applicator makes drenching only seconds longer than putting on endectocide. Bison, camelids, sheep and elk take it readily, but the product is extra label on these species, which means it needs a veterinary prescription.
The price of insecticides has dropped considerably, which means they are still a good option for lice.
Combining endectocides with Safeguard is the one-two punch that Canadian cattle producers need to bring internal worms and external parasites under control.
The benefits include better performance, increased feed efficiency, increased resistance to disease and higher reproductive rates in heavily parasitized cattle.
The cycle of transmission to young calves can be broken with treatment on pasture.
