Parasites reduce cattle feed intakes: Strategic deworming vital for sustainable program

MADISON, N.J. — Reduction in feed intake is the No. 1 effect parasites have on animals.

“Parasites cost the cattle industry over $2 billion per year just in treatment cost and lost production,” said Harold Newcomb, technical services veterinarian for Merck Animal Health.

Worms do three things to animals, Newcomb said during a webinar.

“Animals with worms won’t eat as much and then you’ll see a reduction in production that can be in daily gain, reproduction efficiency or milk production,” he said. “The third thing is impairing the immune response to vaccinations.”

The impact of parasites occurs in all segments of the cattle production system from the cow/calf operation to the stocker and also with feedlot cattle.

“If animals are parasitized, they’re going to eat less and you’ll see a reduction in the production of those animals,” Newcomb said.

“You can see a 10% to 12% increase in the conception rates and 30- to 40-pound heavier weaning weights than with animals not strategically dewormed,” he said. “If you have 100 cows, that is 10 to 12 extra calves.”

It is important for cattlemen to understand the life cycle of worms, Newcomb said, to be able to develop an effective treatment program.

The adult worms are in the cow and they produce eggs that pass out the feces. After the larvae hatch from the eggs, they crawl up the blades of grass that the cows eat on the pasture and the life cycle repeats.

“Depending on the age of the animal, that life cycle can be repeated in as little as three weeks,” Newcomb said. “From 90% to 95% of the parasites are on the pasture in the form of eggs and larvae and from 5% to 10% are in the host or cow.”

Therefore, if a cattleman is only going to treat the cow, he must figure out a way to treat the cow that has the most negative impact on the worms in the cow, as well as on the pasture.

“All the dewormers in the U.S. fit into one of three classes and each class kills a worm in a different way,” Newcomb said. “But each member of a class kills the worms in a similar way, so you need to rotate between classes and use them in combination.”

A fecal egg count reduction test is a tool that can be used to determine the level of parasitism in a cattle herd.

“For this test, you take 20 samples at the time you treat the animals and 14 days later, take 20 more samples,” Newcomb said. “The 14 days are important because that is long enough to give any dewormer a chance to work, but not too long where the life cycle can repeat itself.”

For the past 10 years, Newcomb said, Merck has maintained a fecal egg count reduction test database to evaluate the efficacy of different classes of dewormer products.

“Pour-ons have an average efficacy of 51% and to have successful deworming 90% or better of the worms must be killed,” Newcomb said.

“By using two products together, a pour-on with Safe-Guard the efficacy jumps to 99 % effective,” he said. “And using two or more products in combination and concurrent will help to extend the life of each compound by 10 to 20 years.”

Newcomb advises cattlemen to do diagnostic testing to figure out the level of parasitism within the herd and to determine what parasites are present.

“Develop a deworming program targeted for the specific problems you have in your operation,” he said. “When you do that, sustainability will go way up because you’re not taking the shotgun approach to deworming.”

Cattlemen should use the full dose of each dewormer when treating their cattle.

“One thing cattlemen have in common is we underestimate the weight of cattle, but you need to know the actual weight to give the dose correctly,” Newcomb said.

“All cows don’t weigh 1,000 pounds. The average weight for cows in the U.S. is 1,300 pounds,” he said. “For a sustainable program you need to dose the animals by their weight not an average weight because then we’re under dosing half of the animals.”

The website, www.safeguardworks.com, has information to help cattlemen determine the optimal time to treat cattle, and it has a dosage calculator to calculate the amount of product that is needed to treat a herd.

“Deworm your cows six to eight weeks after the grass greens up when the cow is harvesting the larvae off the pasture and just as they’re getting ready to mature and start producing eggs,” Newcomb said. “That will make the pasture parasite safe through the fall.”

For more information about Merck Animal Health go to www.merck-animal-health-usa.com.