Control The Right Parasites At The Right Time


Beef producers and feeders can improve their parasite control program by making sure they select a dewormer that will control the right parasites at the right time – and which leads to the most productive gains when cattle are marketed.

That’s the recommendation of Dr. Jerry Woodruff, senior veterinarian for Boehringer Ingelheim Vetmedica, Inc. His message comes at a critical time in beef production, in which management of animal health and other production costs are crucial to the fate of profit potential.

“Internal parasite effects in cattle can be difficult for producers and feeders to grasp,” Woodruff says. “But even minimal levels of parasites can have a negative impact on the immune system. It’s important to identify the parasites that impact your herd and make sure you have excellent control of the ones that impact animal performance.”

Know parasite “colors”  Even though parasites are minute critters, vets sometimes distinguish them by their colors. For example, the “brown stomach worm” (Ostertagia ostertagi), is recognized as the most economically damaging parasite for cattle, Woodruff says.

However, the “black scour worm” (Trichostrongylus longispicularis) is of little relevance to cattle in the U.S., he says, citing research by Dr. Thomas Yazwinski, a professor at the University of Arkansas Department Animal Science. The black scour worm is a problem with Australian sheep industry.

“Most deworming products control more than 30 internal and external parasites and stages of parasites,” Woodruff says. “Producers should ask their veterinarian what key parasites need to be controlled in their geographic area. For this reason, utilizing a dewormer that controls adult brown stomach worm, as well as L4larvae, and inhibited L4larvae should be the first consideration.”

Diagnosis  Fecal egg count (FEC) is a proven method of evaluating internal parasite infestation in cattle. FEC is relatively inexpensive and easy to accomplish. It provides the vet and producer with a rough idea as to the parasite load that an animal is carrying.

Woodruff says FEC is performed by mixing a known volume of feces with either a saturated salt or sugar solution. “This allows parasite eggs to float to the surface where they can be captured on a microscope slide, evaluated and counted under magnification,” he explains.

FEC results are reported as “eggs per one gram of feces.” Woodruff notes that misunderstandings about the level of parasite infestation occur with FEC results reported as eggs per three grams, or eggs per five grams of feces. “Some results are reported as either positive or negative, +1, +2, +3 and so on, or other qualitative value,” he says.  Performing an FEC is a rough estimate of the magnitude of internal parasite level.  A fecal egg count reduction test (FECRT) allows for evaluating parasite drug treatment effectiveness.

“FECRT utilizes two fecal samples from the same animal, taken two to three weeks apart,” he says. “A calculation can then be made as to percent reduction in internal parasite eggs from the first to second sample.” (FEC 1st sample – FEC 2nd sample / FEC 1st sample X 100 = FECR %.)

“The first FECRT sample is often collected just prior to, or at the time of, anthelmintic treatment in an attempt to evaluate dewormer efficacy,” Woodruff says. “Timing of the follow-up sample is important to accurately assess effectiveness of a parasite control product.”

He points out that adult parasites not removed by treatment may not shed eggs for 14 days after exposure to the treatment drug. This could cause an artificial underestimating of remaining parasite levels.

“If the second sample is collected more than three weeks post-treatment, it could possess eggs from newly acquired infestations,” Woodruff says. “There could be egg shedding variations due to diet change effects on the adult worm, or in the case of inhibited brown stomach worm, a new crop of larvae may have developed into mature, egg-laying adults.”

Coproculture is a further diagnostic process that helps a vet or producer identify the genus and species of internal parasites within the feces. The fecal sample is incubated for two to three weeks, allowing eggs to hatch into larvae. With this information, a vet can tailor a dewormer program specific to the family of parasites present in a group of animals.”

Dewormer persistency The persistent control provided by a dewormer is another consideration when selecting a parasite control product. “Persistency describes how a dewormer continues to fight parasite infestations after application,” Woodruff says. “Increased persistency can result in fewer parasite eggs shed, reduced pasture parasite levels and increased opportunities for weight gain, as well as higher production for dairy animals.

Cydectin® Pour-On (moxidectin) from Boehringer Ingelheim Vetmedica is persistently effective against the most economically significant parasite ­– the brown stomach worm – as well as lungworm and nodular worm. That’s based on FDA approved label indications.

Cydectin Pour-On controls brown stomach worm twice as long as Ivomec® Pour-On (avermectin) and the leading generic.1In addition, Cydectin Pour-On shows persistent activity against three key species, unlike Eprinex®, which offers no persistence against important parasites common to cattle.

In the comparison, CydectinPour-On controlled brown stomach worm 28 days, compared to 14 days from Ivomec and Noromectin® Pour-on. Cydectin controlled lungworm 42 days, compared to 28 days for Ivomec and Noromectin. All three dewormers controlled nodular worm for 28 days. Dectomax® Pour-on controlled all three parasites 28 days. However, Ivomec® Eprinex® showed zero control of brown stomach worm and nodular worm and only 21 days control of lungworm.

Better weight gain  Parasites can interrupt cattle performance, meaning that long-lasting parasite control can boost the bottom line. According to a Louisiana State University study which summarized advantages in weight gain when various pour-on topical dewormers were used, Cydectin treated stocker cattle had higher overall weight gain and average daily gain over a 112-day period.

The Cydectin treated cattle gained 338.8 lbs. and had a 3.02-lb. ADG. That compared to 323.4 lbs. and a 2.89 ADG for Dectomax treated cattle; 305.8 lbs. and 2.73 ADG for Ivomec treated cattle; 327.8 lbs. and 2.93 ADG for Eprinex treated cattle; and 279.4 lbs. and 2.49 ADG for a control group. (The best growth performance in this study was achieved by cattle treated with Cydectin Pour-On regardless of bodyweight categories measured.2)

Woodruff concludes that producers should compare product labels for persistency that provides both parasite control and enhances cattle performance. “Again, increased persistency helps reduce the parasite load for the animal,” he says. “It also reduces the parasite load on the pasture. It doesn’t matter how many parasites a product controls if it doesn’t control the ones with the greatest economic impact on your herd.

“The type of persistency offered by Cydectin Pour-On is needed if producers are to effectively control parasites over extended periods of time. It should be considered for use in an overall parasite program that provides producers with the opportunities to see effective parasite control and top cattle performance.”

For more on Cydectin® Pour-on and overall parasite control, go to

1 Myers, GH and Keith, EA. Nationwide cattle survey: Zeroing in on parasites. Large Animal Veterinarian, 1993; 48:30–32.

2 J.C. Williams et al., Veterinary Parasitology 85 (1999) 277-288.


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