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Effective deworming programs are integral to cow comfort

Brian Miller for Progressive Dairyman Published on 06 August 2018
Cows in pasture

In the dairy industry, we often underestimate the power of parasites. Parasites have the ability to impact conception rates, milk production and immunity. It’s often assumed a herd is parasite-free simply because there are no outward signs of parasitism.

However, parasites commonly remain unseen as subclinical cases. Even in confined dairy herds where cows do not have access to pasture, controlling external parasites is a key aspect of keeping cows comfortable.



It’s important for dairy producers to have a well-thought-out parasite control program put in place with the guidance of their herd veterinarian. Rubbing, itching, violent tail switching and restlessness associated with external parasites such as lice and mange is reflected in reduced feed intake and resting time, robbing cows of potential milk production.

In confined dairy operations, a strategic deworming program can enhance cow comfort, health and performance.

As summer comes to a close, now is the time to begin thinking about deworming protocols. Here are six factors that contribute to an effective deworming program:

1. Know the enemy

Lice and mange are a constant challenge for confined dairy operations:


  • Mange mites are considered the most concerning of late-fall and winter parasites in most dairy herds. There are two kinds of mange, chorioptic and sarcoptic. It only takes a small number of either of these mites to create widespread lesions and dermatitis.

o Chorioptic mange is the most common mange mite affecting dairy cattle. Clinical signs include hair loss, crusting and wrinkled skin near the tailhead, areas immediately adjacent to the tailhead and just above the rear udder and medial thigh.

o Sarcoptic mange is much less common, but it is a reportable disease. Clinical signs include skin lesions on the tail, neck, shoulders, brisket, rump and inner thighs.

  • Lice are another common parasite. There are two types of lice, biting and sucking. One feeds on skin debris; the other sucks blood. Breaking their life cycle can be a challenge. By the time producers see symptoms of hair loss, the population and number of eggs present on the cows’ hair coat have skyrocketed.

2. Get the timing right

Getting your money’s worth out of a pour-on dewormer involves application at the appropriate time. The following are general guidelines:

  • An annual pour-on application in the late fall or early winter is an ideal time to aid in the control of mange and lice populations. Mange is usually a problem in the winter months because cooler temperatures and longer hair coats favor parasite survival. All adult animals in the lactating herd should be poured at one time to establish baseline control.

  • Following the annual application, all new herd additions (dry cows, first-calf heifers, bulls and purchased animals) need to be poured 14 days prior to entry into the adult herd. Failure to do so can lead to a re-infestation of lice and mange if incoming animals are harboring these parasites.

  • If your adult herd does have access to pasture, an additional round of deworming should take place around four weeks following spring turnout to help control internal parasites.

Parasite challenges can change based on climatic conditions, so check with your veterinarian to determine what preventative measures work best for your herd.

3. Maximize efficacy


In order to obtain the full benefits of a dewormer product, the treatment must be applied correctly. When using a pour-on dewormer, carefully apply along the topline in a narrow strip from tailhead to withers. This will reduce product runoff and maximize efficacy.

A common practice is to treat for the average weight of the cows within a herd. Although convenient, dosing to average weight will under- or overdose many cows.

Underdosing will diminish effectiveness of the dewormer and contribute to parasite resistance, while overdosing wastes product and money. A scale, weight tape or a cull weight slip can be used to determine cow weight and will increase dosing accuracy.

4. Follow the label

It is essential to read and follow all label directions. When choosing pour-on dewormers, use only those approved for lactating dairy cows. Off-label use of an unapproved pour-on dewormer may be tempting because of the cost savings, but it’s a dangerous practice.

Any amount of an unapproved product detected in milk is illegal and can lead to fines and lost milk sales.

5. Reduce parasite resistance

Resistance occurs when a parasite population is able to survive treatment from a dewormer that was once effective. As discussed, providing the correct dose to all individuals within a herd is critical to reducing the opportunity for parasite resistance to occur and to ensure product effectiveness.

6. Work with your veterinarian

Your herd veterinarian is your best cattle parasite resource and will help develop a control program tailored to your operation’s specific needs. They can provide treatment options approved for lactating cows and direction on correct dosage and application.

Be sure to use a product that can control internal and external parasites, is approved for lactating cows and has a 100 percent product satisfaction guarantee. Controlling mange and lice populations contributes to keeping cows healthy, comfortable and productive.  end mark

PHOTO: An additional round of deworming should take place around four weeks following spring turnout to help control internal parasites if herd has access to pasture. Photo by Mike Dixon.

References omitted but are available upon request. Click here to email an editor.

Brian Miller
  • Brian Miller

  • Senior Professional - Services Veterinarian
  • Boehringer Ingelheim
  • Email Brian Miller