August 15, 2019

Disappointed in Average Daily Gains on Your Operation? Parasites May Be to Blame.

Understanding the parasite life cycle and strategic treatment can help improve performance in all stages of cattle production.

DULUTH, Georgia. (Aug. 15, 2019) — It’s no secret that heavy worm loads negatively impact overall herd health and producers’ bottom lines. In fact, parasitic infections have been estimated to cost livestock producers more than $3 billion in economic losses each year.1

“The infestation of brown stomach worm and other internal parasites can suppress appetite and reduce feed intake, resulting in disappointing average daily gains and weaning weights. It can also lead to problems with reproduction in cows and heifers,” said Joe Gillespie, DVM, Boehringer Ingelheim. “Controlling these parasites is a proven practice to improve performance in all stages of cattle production, while also giving you a significant return on investment.”2 

Understanding the parasite life cycle 

As concern about the resistance of cattle parasites to dewormers continues to rise, gaining a basic understanding of the internal parasites that impact your herd is the first step producers can take to establish a cost-effective deworming approach. Dr. Gillespie breaks down a basic parasite life cycle below: 

  1. Adult parasites lay eggs in the gastrointestinal tract of cattle.
  2. Eggs are expelled from the cattle through feces. 
  3. Eggs hatch and develop into infected larvae. 
  4. The infected larvae crawl onto the grass that cattle graze on. Feed bunks or waterers contaminated with feces can also expose cattle to larvae. 
  5. Larvae are ingested by cattle. 

This process will continue to repeat itself unless parasites are managed. At the end of the grazing season, some internal parasites, such as the brown stomach worm (Ostertagia ostertagi), will bury themselves in the stomach wall, stay dormant until spring, emerge and start egg-laying again. 

“Knowing the life cycle of internal parasites can help producers establish an appropriate deworming timeline,” asserted Dr. Gillespie. “It’s also important to note that there are technically four larval stages, and not all dewormers are labeled to protect cattle against the final larval stage.” 

To prevent parasite resistance, reduce subsequent contamination of pastures, and provide cost-effective parasite control, Dr. Gillespie recommends using a dewormer with demonstrated efficacy against major intestinal parasites including O. ostertagi L4 and inhibited L4, as well as tapeworms, prior to the grazing season. 

Not only is it beneficial for producers to be strategic in selecting the right dewormer(s), he also encourages producers to weigh calves to determine the right dose, and work with their veterinarian to identify the best time to treat cattle. 

Timing is everything 

Parasite populations vary widely, depending on climate, geography and type of operation. In general, temperatures between 60  and 80 degrees Fahrenheit, and with at least two inches of rainfall per month, provide excellent propagation conditions.3 Dr. Gillespie explains that it’s important to take all environmental considerations into account when deciding the timing of treatment. 

“With a high stocking rate in pastures, I recommend using a dewormer twice per year to help keep animals on track,” he said. “Most producers use some form of dewormer in the spring as cattle go out to pasture. A second treatment should be given in late fall or early winter, along with a lice control to help manage ectoparasites, as well.” 

In the cattle-feeding sector, it is common to see an oral dewormer used upon arrival at the feed yard, and a corresponding topical treatment used to help with flies or lice. “With a high-energy, high-starch diet and no grazing, fewer internal parasites are seen, but they can become a problem, so deworming upon entry is the best strategy,” stressed Dr. Gillespie.

Local veterinarians have experience with other operations in the area, so producers are encouraged to consult them when thinking through deworming decisions. 

Veterinarians can also help producers perform routine fecal egg counts to ensure their dewormer is working effectively.

“An effective deworming program doesn’t look the same for every operation,” concluded Dr. Gillespie. “But understanding the parasite life cycle, identifying key timing and keeping your veterinarian involved are all great ways for producers to control parasites in every herd without breaking the bank.”



1 Bagley C, Healey M, Hansen D. Internal parasites in cattle. Beef cattle handbook. Extension Beef Cattle Resource Committee, University of Wisconsin Extension. Available at: Accessed April 24, 2019. 

2 Stromberg BE, Vatthauer RJ, Schlotthauer JC, et al. Production responses following strategic parasite control in a beef cow/calf herd. Vet Parasitol 1997;68(4):315–322.

3 Morter RL, Horstman L. Treating for internal parasites of cattle. Purdue University Cooperative Extension Service, School of Veterinary Medicine. Available at: Accessed April 24, 2019. 

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