During the height of the summer, cattle can face an increase in parasites – both internal and external – that can wreak havoc by disrupting feeding and slowing growth. That’s because producers typically tackle these pests in the spring (including deworming and horn fly control) before pasture turnout and as pest season begins. Yet many don’t revisit the need for added measures in midsummer, as parasite load and fly pressure increases, leaving cattle potentially less protected inside and out.

Fortunately, producers can kill two birds (or parasites) with one stone by adding a midsummer deworming treatment that also offers fly control benefits. Several “dewormers” are actually “endectocides,” meaning they control both internal or “endoparasites” (such as worms) as well as external or “ectoparasites” (such as horn flies).

Starting from the inside

Producers know using dewormers can help increase productivity, but these products are often administered based on when it is convenient, usually in the spring when cattle are turned out to pasture and again in the fall. This timing is not necessarily when it is most appropriate or most effective.

Parasite burdens and egg production decrease during the winter, then begin to rise in the spring and increase over the summer, which can result in significant pasture contamination and exposure of animals to more parasites. However, if animals are dewormed, especially as they move to new pasture, the parasite burden in the animals can be reduced and the pasture contamination kept to a minimum.

Timely use of a dewormer both in the spring and midsummer – also known as strategic deworming – can reduce the animal’s parasite burden, which means the number of parasite eggs in the animal’s manure will decrease. This reduction of the parasite burden can result in improved growth, body condition and pregnancy rates.

In fact, studies have shown strategically treated calves experienced greater average daily weight gains that can amount to nearly an additional 50 pounds at weaning. And cows strategically treated with dewormers have been shown to have increased reproductive performance, with a 12 percent increase in pregnancy rates and increased milk production.

Moving to the outside

While addressing fly control in the spring can be very effective, producers may experience ongoing horn fly challenges in midsummer. These can include:

• A resurgence of horn flies, often brought on by weather changes
  
  
• Eartags and pour-ons applied early in the season being depleted, requiring reapplication, especially in locations with longer fly seasons

Fortunately, in addition to their internal parasite benefits, some pour-on dewormers also provide up to 28 days of persistent activity against horn flies. For optimal control of horn flies, these products should be used as part of an integrated program utilizing other methods to provide extended control.

Creating a midseason strategy should involve asking yourself the following key questions:

• How much of an issue is the midsummer fly pressure, meaning how quickly do you need to address it?
  
  
• What are your farm capabilities, such as practicality of gathering animals for treatment, employees and time available, budget?

Identifying the need and evaluating the efficacy of your management program requires routine monitoring. Horn fly abundance should ideally be assessed weekly throughout fly season. While whole body counts provide the most accurate assessment, they are difficult to conduct.

A more practical means is counting flies on the shoulders, sides and back of 10 to 15 cattle. When average counts exceed 200 flies per head, additional control is probably needed.

Limiting fly-friendly environments

Speaking of pastures, it’s also important to consider the dewormer’s impact on the pasture and the things that live in the pasture, such as dung beetles.

Studies have shown fecal residues of moxidectin are less toxic to dung-dwelling insects than are residues of doramectin, eprinomectin and ivermectin. In more than 10 studies, moxidectin has been shown to have little or no effect on dung beetles.

By breaking down dung pats where common cattle pests and parasites lay eggs and develop, dung beetles can help reduce pest populations. Dung beetles have been proven to provide benefits estimated to be worth upward of $380 million annually in the U.S. Healthy dung beetle populations have been shown to significantly reduce both horn fly and nematode populations.

Taking a strategic approach to deworming and fly control can give producers a one-two punch when it comes to protection against parasites. Correctly timing your application and choosing the right products can help ensure an effective and efficient defense of your cattle throughout the season.  

PHOTO: Many producers do not revisit the need for added parasite measures in midsummer, as parasite load and fly pressure increases. Photo courtesy of Bayer Animal Health.