Only deworm “high risk” animals. These animals include younger cattle (<16 months), especially calves. Older cattle generally develop a tolerance to gastrointestinal parasites and are better able to cope with their presence than younger animals.
Do not deworm by the calendar. Cattle should only be dewormed when they need it, not simply because of the season or time of year. A single composite fecal egg count can be performed for a group of cattle to evaluate current parasite load.
Perform selective non-treatment. This practice ensures that there are sufficient parasite numbers that are unexposed to an anthelmintic which will help maintain a population of susceptible parasites (referred to as “refugia”). To implement this strategy, producers should deworm all animals in their high risk groups except for the top 10 to 15% heaviest/best performers.
Utilize combination treatments. This strategy involves simultaneous treatment with at least two drugs in different classes (e.g., one benzimidazole and one macrocyclic lactone; levamisole and one benzimidazole, etc.). With this approach, any parasites resistant to one drug class will likely be susceptible to the other class, which would greatly reduce selection pressure for resistance to either drug. This method is much more effective in controlling the development of resistance than rotating between drug classes.
Avoid under-dosing. Under-dosing commonly occurs when animals are not weighed prior to treatment such that a lower dose is used than is required for maximum effect. This is a serious problem that certainly contributes to the selection of resistance. To avoid under-dosing, be sure weigh animals to determine proper dosage. Ideally, a set of scales is used for this; however, if scales are unavailable, use of an appropriate weigh tape is better than nothing.
Examine grazing practices. Short forages resulting from overstocking and overgrazing pastures forces animals to graze closer to manure piles and increases the risk of parasite exposure. Implementing rotational grazing and giving paddocks adequate rest (4-5 weeks) can also help break the parasite life cycle and reduce risk of exposure.
Continue to evaluate the program to ensure efficacy. This can be accomplished by performing a fecal egg count reduction test every few years.