Jody Wade, DVM, Boehringer Ingelheim, said he’s seen internal parasite burdens increase on a number of cattle operation diagnostic reports over the last two years. Intensive rotational grazing, overstocking and grazing forages too closely to the ground may be contributing to the increase.

To manage internal parasites, Dr. Wade recommends working with your veterinarian through the following steps:

     1. Determine when deworming is needed

Diagnostics help us understand the animal’s parasite load to determine when treatment is warranted. A fecal egg count (FEC) is an effective tool to determine when cattle should be dewormed, and is normally conducted at the beginning of a grazing season. Cattle with egg counts below threshold levels do not need to be treated.

     2. Identify the parasite species to control

To identify which species of internal parasites are present, a coproculture should be conducted. This is done at the diagnostics lab by placing parasite eggs in an incubator. Once the larvae hatch, they are speciated to determine which parasites —Ostertagia, Cooperia or others — are prevalent in order to guide treatments.

     3. Choose the right treatment

Each class of dewormers has its own strengths and weaknesses. Certain classes are more effective against specific parasite species. Choosing the right active ingredient and avoiding repeated use of the same class of dewormer can help prevent development of resistant populations of parasites.

     4. Administer the correct dose

Be sure to read the label and administer the correct dose based on animal weight. A common practice is to dose dewormers according to the average weight of the herd. This is convenient, but it can over- or under-dose a significant number of the cattle, reducing the effectiveness of the dewormer. Investing in a scale and administering a low-dose product offers more accurate dosing and reduces product waste.

     5. Determine the effectiveness of your deworming practice

Conducting fecal egg counts both before and after deworming can provide an indication of the effectiveness of your deworming program. The goal is to achieve a kill rate of 95%. The FDA considers a kill rate less than 95% to be an indication of resistance to the product’s active ingredient.

“Parasites that survive deworming are likely resistant to the product. They then reproduce, further increasing the population of resistant parasites,” Dr. Wade said. “That means the next year, the parasite problem will be worse. That’s something we definitely want to avoid at all costs.”

Use refugia to minimize resistance development

To avoid or prolong the development of resistance, Dr. Wade encourages leaving a portion of the parasite population in “refuge” from dewormers. Parasitologists have recognized refugia as the single most important factor in delaying the onset of parasite resistance. It can be accomplished by selectively not deworming a percentage of animals in the herd.

“Animals with low fecal egg counts, thrifty high-gaining calves or the older, heavy cows may be animals to consider leaving untreated as refugia,” added Dr. Wade.

How many and which animals to select for refugia is different for every producer, so it’s another important reason to consult with your veterinarian.

“Using science and the expertise of your local veterinarian when developing your deworming strategy is the right thing to do for your herd and for the beef industry,” Dr. Wade concluded.

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