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Don’t let internal parasites steal profits from your pasture cattle:  Remember to deworm

Oct 28, 2021

Don’t let internal parasites steal profits from your pasture cattle:  Remember to deworm

By Grant Crawford, Ph. D., Merck Animal Health Cattle Technical Services
Cattle producers need to look no further than their favorite cattle magazine or website to realize that there are a multitude of products available that claim to add value to their cattle. Of all these available products, one might be surprised to find that the category that adds the most value to the cow/calf and stocker operations is dewormers. According to an analysis of beef cattle production technologies1, using a dewormer in the cow/calf herd can add $201/head to the profitability of the cow. This added value is due to improved weaning weight on the calf and improved pregnancy rate on the cow. For stockers, the added value is $24/head. This is due primarily to added weight gain.

The impact of worm infection in cattle begins on grass. Cattle consume grass that is infested with worms as soon as they are turned out to green grass. Worms on grass are resilient, they can survive cold winter temperatures as well as hot, dry conditions in the summer. Once consumed by cattle, worms damage the gut lining and cause alterations in nutrient digestion. The primary effect of this is a decrease in feed intake.  In addition, nutrient absorption can also be negatively affected by parasitic infections. Therefore, not only is nutrient intake decreased, but the absorption of nutrients is decreased as well. This can lead to decreased weight gain, milk production, and reproduction.

Worms also affect cattle health. The immune system recognizes worms as a parasitic invader and will work to protect the animal from this attack. When this happens immune resources that usually are available to fight viruses and bacteria are redirected toward fighting the parasitic infection. Because of this, it is a good idea to ensure that cattle are worm-free prior to vaccinations to allow vaccines to properly immunize cattle against viruses and bacteria. 

In a study to assess the health and performance benefits of deworming cattle on grass and at feedlot entry2, stockers that were strategically dewormed with Safe-Guard dewormer prior to grass turnout and again at 28- and 56-days post-turnout were 53 pounds heavier after 118 days than steers that were not dewormed. Upon feedlot entry, steers were either dewormed again with Safe-Guard or were not dewormed.  Cattle that were dewormed on pasture as well as upon feedlot entry were 130 pounds heavier at the end of the feedlot phase (an additional 121 days) than cattle that were never dewormed. Cattle that were dewormed were healthier as well. Cattle that were dewormed on pasture and prior to feedlot entry had 2% morbidity and 0% death loss, while cattle that were not dewormed had 18% morbidity and 2% death loss.

For these reasons, deworming should be considered the foundation of any health and nutrition program. It is best to strategically utilize dewormers to stay ahead of the worm’s life cycle. In mature cows it takes 6-8 weeks for worms that are ingested from grass to begin to shed eggs back onto the pasture. If cows were dewormed after a killing frost in the fall or winter, they should be worm-free until they are exposed to green grass again.  Therefore, the best time to deworm is 6-8 weeks after green-up. For stockers, the life cycle from worm ingestion to egg shedding is 4-6 weeks. Therefore, stockers should first be dewormed prior to grass turnout, and then again 4-6 weeks later. In some cases, a third deworming treatment another 4-6 weeks after the second treatment may be necessary. 

One other important consideration is fall or winter deworming after a hard frost.  A hard (or killing) frost is defined as air temperatures 28 degrees F or below. Once pastures experience a hard frost, free-living parasites will burrow into the soil, drastically reducing their availability for consumption by grazing cattle. Deworming cattle after a hard frost is therefore an important practice to reduce worm loads until cattle are exposed to green grass again in the late winter or spring. This is particularly important for spring-calving cowherds. Approximately 75% of fetal growth occurs during the third trimester, and the gestating cow or heifer therefore must channel a large proportion of nutrients toward supporting that growth. If cows and replacement heifers are not sufficiently dewormed at this time worms will take away important nutrients that should be directed toward the gestating calf. Those nutrients are also taken away from maintaining cow and heifer body condition, which is an important factor for subsequent rebreeding.   

Safe-Guard cubes are a safe and highly effective option to deworm without having to gather cattle for processing through a chute. Safe-Guard cubes successfully deworm cattle in a simple, one-day feeding and are available from a variety of feed manufacturers. 

One way to ensure dewormer efficacy is through a Fecal Egg Count Reduction Test (FECRT). These FECRTs analyze egg counts in feces as a measure of worm load in that animal. A FECRT can help producers determine:
  1. if their cattle need to be dewormed
  2. if their deworming program is effective

Contact your CFE Beef Specialist to request a FECRT kit to assess dewormer efficacy and worm load in your herd.     

Deworming is not only important; it is the most important thing we can do to enhance profitability in cow/calf and stocker operations.  To best utilize these tools, be sure to use a quality dewormer and work with the worm life cycle to keep cattle productive through the entire grazing season.


1Lawrence, John D. and Maro Ibarburu.  2007.  Economic analysis pharmaceutical technologies in modern beef production in a bioeconomy era.
2Smith, Robert A., Karen C. Rogers, Scott Huse, et al. 2000.  Pasture deworming and (or) subsequent feedlot deworming with fenbendazole.  I.  Effects on grazing performance, feedlot performance and carcass traits of yearling steers.  The Bovine Practitioner 34(2):104-114.         


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