Producers need to know which parasites they’re dealing with in order to best target their deworming program.
“A testing program incorporates fecal egg counts (FEC, measured as eggs per gram of feces) and coproculture (hatching larvae in the lab to identify them). When we perform a FEC, we quantify how many parasite eggs per gram of feces are being passed by the animal,” explains Wayne Ayers, DVM, technical consultant veterinarian with Elanco. “The issue with FEC alone is that four of the most common and most costly parasite eggs cannot be identified by looking under the microscope. In order to identify and separate, we must hatch and grow them in the lab.”
Why is it important to identify parasites and understand their relative proportions?
- Each parasite presents a different risk for economic loss.
- The four most concerning female parasites lay eggs at different rates. For instance, a female brown stomach worm will lay about 200 eggs per day, while a female barber pole worm can lay 10,000 eggs a day. Therefore, a 50 egg per gram FEC means something completely different if the eggs are from a brown stomach worm verses a barber pole worm.
Another component of parasite testing is called a fecal egg count reduction test [FECRT], which is used to determine treatment effectiveness. This involves collecting a fecal sample from each animal on the day of treatment and performing a FECRT. Follow-up samples from the same animals are collected seven to 10 days after administering a white dewormer or 14 to 21 days after a macrocyclic lactone.
The results of the before and after treatment FEC from the same animal are then compared. A reduction in eggs per gram must be 90% or greater to say the treatment was effective. When the FECRT is less than 90%, there is evidence there might be some resistance building in the parasite population. The lower the percent of change the greater the evidence of reduced efficacy and resistance to the product used.
Gone are the days of thinking we can eliminate parasites with an injection or pour on, Ayers says.
“The parasites will win if we don’t start managing them to a point that is physiologically tolerable for our cattle and at the same time is economically tolerable for producers,” he says.
Another strategy developed with producers in mind is that any animal, regardless of age, with a body condition score of 4 or less needs to be dewormed.
“It’s not even necessarily that the worms are causing them to be thin, but they need all the nutrients possible to get back to a body condition of 5.5 to 6,” Ayers explains. “I don’t want a parasite load reducing nutrients available to the cow or young stock.”
Additionally, any cattle that are younger than 3 years old need to be dewormed regardless of their body condition.
“Even young stock in good body condition need to be dewormed because they tend to have higher parasite numbers,” Ayers adds. “By treating them, we help prevent carrying them all winter long, then becoming high shedders in the spring, contaminating the pasture, and infecting the next generation at a higher level.”
Read more: A New Approach to Deworming
