How to use dewormers that will control internal parasites

Internal parasites are a problem that every beef producer must face. It is a constant annoyance that can rob a beef operation of its productivity. They impair production by increasing things like energy costs of maintenance, diet digestibility, and immune activity.

They actually have a more significant impact on the profitability of beef cattle than most even realize. Research has shown that weaning weights can be increased by over 30 pounds and pregnancy rates by over 10% with proper deworming. With statistics like this, it would make sense to keep them under check.

Controlling them requires correct planning as well as proper timing. In order to get the most efficiency, you need to use the right dewormer at the right time of the year. Here are some things to look at when planning for your deworming program.

Dangers of internal parasites

The total effect that internal parasites can have depends on several factors. Things like age and even stress levels play a part in infection. Calves are more likely to have them than mature cows. Cows will typically develop a decent immunity to them by around four years of age.

Besides the obvious health problems, reduced productivity can be a severe drain. The most considerable impact is the decrease in voluntary feed intake. The reduction in feed intake is a response due to changes in the abomasum. This decreased intake will cause a reduction in the absorption and digestion of critical nutrients. The economic losses to the livestock industry caused by internal parasites are estimated to be over $3 billion annually.

Though there can be others, four parasites are typically the most common. Hair worms, Lungworms, Liver flukes, and Coccidia, are the ones that most producers see. I review the different symptoms and treatment options of these parasites in a previous post, “4 common cattle internal parasites”.

The main form of transmission for these parasites is that they are present on the grasses that cattle graze. Cattle consume the eggs, and they enter their intestinal tract or abomasum. Parasites lay eggs there, passing through the digestive tract and returning to the environment via manure. These eggs are very resilient and can survive things like extreme temperatures. Kansas State has a paper, “Understanding Internal Parasites in beef cattle,” that goes into a little more detail about the life cycle of internal parasites.

3 classes of dewormers

When it comes to deciding what product to use, while there are many options, what to use depends on a couple of different factors. An important one is which product you used last time. Using the same product all the time can cause resistance to it, thus making it ineffective.

Though there are many different brands at your local feed store, typically, they fall into three categories of active ingredients. Benzimidazole, macrocyclic lactones, and imidazothiazoles are the three different types of dewormers. Among the most common chemicals used on cattle are macrocyclic lactones and benzimidazoles. Macroscylics are either injectables or pour-ons, while benzimidazoles are administered orally.

• Benzimidazoles: found under the drug names fenbendazole, oxfendazole, albendazole, and ivermectin. The commercial names for them are Safe-Guard, Panacur, Synanthic, aValbazen, Ivermectin, Bimectin, Noromectin, and Ivomec.
• Macrocyclic Lactones: are found under the drug names eprinomectin, doramectin, and moxidectin. The commercial names for them are Eprinex, Eprizero, LongRange, Dectomax, and Cydectin.
• Imidazothiazoles: are found under the drug name levamisole. LevaMed and Prohibit are commercial names.

When to deworm

When it comes to deworming, most producers apply it at a specific time of year. Typically it can happen when they are running the cattle through the chutes castrating, and dehorning. However, doing it this way can cause more problems than they solve.

The only natural way to determine the effectiveness of a dewormer is by using a Fecal Egg Count Reduction Test. This test measures the number of eggs present in the pasture before and after administering dewormer. An effective treatment is one that reduces the fecal egg count by 90% or more after treatment. Research from 72 beef operations across the U.S. showed that operations relying on pour-on macrocyclic lactones had a 48% to 75% failure rate, whereas injectable products had only a 15% failure rate.

If, by using the fecal egg count reduction, you find out that your current program is not practical, there are some practices you can use to improve:

Deworming strategies

1. Only deworm “high-risk” animals will include younger cattle, ones less than 16 months, and calves.
2. Do not deworm by the calendar: Cattle should only be dewormed when they need it. An easy way to determine the parasite load of a herd of cattle is to count fecal eggs together.
3. Perform selective non-treatment: To do this strategy, producers should deworm all the animals in the high-risk groups except for the top 10-15% heaviest/best performers.
4. Utilize combination treatment: This strategy involves treatments simultaneously with at least two drugs in different classes. An example of this would be using one benzimidazole and one macrocyclic lactone. Using this approach, parasites resistant to one type will likely be susceptible to the other. This susceptibility would significantly reduce the selection pressure for resistance to either drug.
5. Avoid under-dosing: This typically occurs when animals are not weighed before treatment, meaning they are given a lower dose than is required for maximum effect. This under-dosing is a severe problem that contributes to the selection of resistance.
6. Examine grazing practices: Overstocking and overgrazing force animals to graze closer to manure piles, increasing the risk of parasite exposure. Using rotational grazing and giving pastures enough rest can help break the parasite life cycle and reduce exposure.

Getting the most from your dewormer

It takes a little more than just using a dewormer to make an excellent internal parasite program. The timing and application of the drug play a considerable role. How often you use a particular drug is also a significant factor.

You will need to change the specific drug in order to prevent resistance. Only after exposure to 1 overtime will the parasites develop genetic resistance. So you will need to hit them with something new from time to time.

Now, this means more than just changing the brand of dewormer that you use. As I showed earlier, different brands have the same active ingredient. What you want to do is to change the active ingredient that you use.