Internal parasites in cattle—often called worms—eat away at the performance and marbling potential in fed cattle, even when they’re dewormed properly at arrival. That’s according to research at Iowa State University (ISU), which also suggests deworming stockers or preconditioned calves as a “best management” approach.
In one trial, 43 steers from Southeastern states varying in age and weight were shipped to a southwest Iowa feedyard, where fecal samples guided a division of cattle into high (HI) and low (LO) parasite burdens. All were treated with the recommended dose of eprinomectin to control what were 92% roundworms (strongyles).
“These parasites live in the digestive tracts, where they cause damage to the stomach, steal nutrients and produce a loss in digestive ability,” says ISU Extension lead researcher Chris Clark.
After 24 days, another fecal exam showed all cattle were free of parasites, but effects of the initial parasite burden were still visible, he notes.
They were all gaining at the same rate by then, but the HI group, lighter on arrival and set back in the first weeks, never caught up. They required more days on feed than the LO group and the HI steers tended to have lower marbling scores, dressing percentages, internal fat and backfat at harvest. Being treated for clinical disease more times, the HI side also incurred higher health costs.
Protect your profits
Even a relatively small research trial serves to point out how easily profitability can be decreased, and reinforces the value of effective internal parasite control starting months before the cattle go into a feedyard.
Clark says the Southeast region, source of calves in the study, is known for high internal parasite risk because of long grazing seasons and a warm, humid climate. Still, he says, grazing cattle across the U.S. are at risk of infection from many different parasites and producers should have a strategic deworming plan that fits their operation.
Patrick Gunn, ISU Extension cow-calf specialist, says timing is the first step in strategy.
Producers often deworm cattle before pasture turnout and again when they come off grass, says Gunn. But until the last year or two, most of the deworming agents available on the market were only effective for approximately 30 days. That means the effectiveness of the deworming agents often wear off just as cattle begin picking up a significant parasite load.
He recommends waiting to deworm until after cattle have been on grass for six to eight weeks, or using one of the recently developed extended-release dewormers. Producers in warmer climates should also look into more aggressive deworming plans with a mid-season option if they graze cattle for longer seasons.
Pasture health and rotational grazing play a role in effective parasite management, Gunn explains. Overgrazed pastures tend to result in higher parasite loads for cattle, so good pasture management can lead to healthier cattle.
Impacts in the industry
Another recent study by Clark and Gunn looked at the impact of not deworming Angus stocker heifers upon arrival at the feedlot after all cattle were treated in the middle of their grazing period with an extended-release deworming agent.
The results? Cattle that were effectively managed to reduce or eliminate internal parasites while grazing did not require deworming at the feedyard. “We didn’t note a difference in feedlot performance or carcass merit,” Gunn says.
“I think the broader impact of this is just reinforcing that producers need to have best management practices in place to minimize parasite load,” he says. “For the feedlot producers, they want to sell a heavier carcass; and the cow-calf producers want to send a heavier calf to the feedyard. On both ends of the sector, it would benefit producers to control parasites to maximize weight gain through all phases of the production cycle.”
Clark agrees, adding that the key to all that is better communication between buyer and seller.
“Sourcing good cattle and knowing cattle history can help feedlots know more about how to treat incoming cattle,” he says. “Preconditioned cattle with proper vaccinations and deworming agents are healthier cattle with a higher marketability.”
The first study showed HI cattle made $40 less in total income due mainly to higher treatment and feed costs, and a reduction in carcass quality leading to lost premiums. The cost to deworm a 500-pound calf once is $2 to $6 and, according to earlier ISU research, the largest return on investment in pharmaceutical technology for cow-calf and stocker operations.
Producers may invest in high-quality genetics, feed and nutritional supplements, but those may not pay off without strategic parasite control, they conclude.