The verdict is in: parasites stress their hosts, lower immune response and steal nutrition. And although there are geographical differences in parasite populations, even in the desert, they are lurking. Research has shown that producers in the driest areas of Nevada saw an economic benefit from deworming.

Research also shows that parasites everywhere take their biggest toll on young calves. "The younger the calf, the more susceptible it is to parasites," says Dee Griffin, veterinarian and professor of beef feedlot production management at the University of Nebraska's Great Plains Veterinary Educational Center. As they get older, animals gain some ability to resist and/or successfully deal with parasites. "So deworming a 5-year-old cow maybe is a waste of time, unless you're in parasite heaven; then it may be affecting milk production," Dr. Griffin says. "But all calves are susceptible to parasites."

Today parasite control is a simple and inexpensive task. "We've never had such good products as we have now," Dr. Griffin says. "But timing and coordination will muck it up. We waste money." Figure: if a calf weighs 300 pounds, and a cow 1300 pounds, you have to spend four times as much money to deworm the mother. "You're better off to deworm the calf twice," Dr. Griffin says. "Unless you're in parasite heaven and you have to deal with both."

Mississippi qualifies as parasite heaven, no doubt. "Deworming, for our area, is pretty critical. We'll see calves die from parasitism," says Terry Engelken, veterinarian and associate professor at Mississippi State University. "The younger the animal, the more detrimental the effects of parasites. It really is critical from a weight gain standpoint. And if we expect vaccines to work, we need a deworming program."

The program starts early. "Typically for our area, somewhere between two to four months of age through to weaning, we try to get two doses of dewormer into a calf," Dr. Engelken says. He suggests that the second time should be at least three weeks prior to the weaning date. And depending on the product used, "it would still probably pay to hit them again at weaning."

Immune response and weight gain
"The producer will give up weight gain by not using parasite control," Dr. Engelken says. "Arguably the most cost-effective management practice we can do is deworm calves."

Tom Wilburn agrees. He's a cow-calf producer near Columbus, Miss., and sells his calves through a video sale, together in a pool with some of his neighbors. These preconditioned calves are dewormed twice while still suckling. Mr. Wilburn conducted his own experiment to test the value of parasite control.

"Twenty five years ago, very rarely did anybody deworm a calf on its mother," he says. "We thought any infection would be very slight because they were mostly drinking milk and were not eating enough grass." So he divided calves into two groups, only one of which were dewormed. "We found out in 60 days that the dewormed calves had put on 18 more pounds. We became great believers in it."

The result Mr. Wilburn observed comes in part thanks to the nutrition-stealing habits of parasites. "Parasites are real hungry guys that take nutrients away that calves need to develop an immune response," Dr Griffin says. "They tend to lean on protein, which we're short on at certain times of the year. Calves can starve to death from a protein deficiency, no matter what you're feeding them."

Dr. Griffin has a photo he uses to illustrate what damage parasites can do. The photo shows two black steers side-by-side. They came from the same ranch, but somewhere along the line, one calf became parasitized. At the time of the photo, it was just a "dying piece of flesh," Dr. Griffin says. "But there was no evidence of disease. Instances like that got my attention."

The malnourishment goes in hand with diminished disease resistance: if parasites are not controlled, there won't be enough fuel available for them to mount a proper immune response. "Then we don't get what we need from those vaccines, probably because of decreased numbers or function of the immune system's killer 'T' cells," Dr. Griffin says. "I've never seen a set of data where we didn't see an improved immune response after deworming." Most vaccines warn of this right on the label.

A study done at Oklahoma State University followed calves from the sale barn through backgrounding, the feedyard and the packinghouse. They were dewormed at different times and rates. "The calves not dewormed early, even if they finally were dewormed, never caught up with those that were dewormed early. Deworming paid in spades," Dr. Griffin says. "The same paper looked at carcass quality, and it showed that even if there had been no difference in weight, the difference in quality would have paid for the deworming."

The biggest lingering concern about preconditioning is the economic return-whether or not it pays. "But the data is clear that the gain realized will far exceed the cost," Dr. Griffin says. Various studies have demonstrated a 10 to 50 pound advantage from preconditioning. "A lot of that, I think, is controlling parasites."

Looking at calves entering the feedlot, "in round numbers, a calf properly prepared is worth 5 percent more and you can be assured you'll get all your money back," Dr. Griffin says. "Our data says 10 percent more is still a good buy."

External parasites
Randy Koenig, a veterinarian at the Twin Valley Veterinary Clinic in Dunlap, Iowa, preconditions around 20,000 calves each year. The calves are part of the Weston Iowa Feeder Calf Association, a source-verified organization for the past 30 years. The members follow the recommendations from the Iowa Preconditioning Committee, which advise grub and lice control at least three weeks prior to sale.

Grub control timing is important because of the life cycle of the grub, Dr. Koenig explains. Once they are licked and consequently ingested, they line up in the esophagus or on the spinal cord before migrating to the epidermis and poking holes out. They need to be killed before they get that far. "If you kill it while it's in the esophagus or the spinal cord, you can cause bloaters or down animals," Dr. Koenig says. "Once they get a chance to damage the hide, the damage stays on the hide." Even if the holes heal over, the scars will remain though the animal's life.

"Those parasites can do some significant hide damage," Dr. Engelken adds. "The hide is one of our most important byproducts." A hide is worth around $55; grub damage will cause that value to fall to around $30.

External parasites can detrimentally affect weaning weights too. "There have been studies with proper fly control," Dr. Engelken says. "We may pick up 4 to 6 percent more weaning weight because instead of fighting flies the cows are eating and milking."

Although the Iowa Preconditioning Program leaves deworming optional, Dr. Koenig recommends it strongly to his clients. "We want calves deloused and dewormed two weeks before they go into the stress of weaning," he says. "When an animal becomes sick at weaning, it will affect his health later on and carcass quality too." Dr. Koenig says most producers he sees do have a deworming program; he estimates that around 85 percent of the calves are dewormed before they're sold.

"Preconditioning is an ever changing process because of the new technologies out there all the time," Dr. Koenig says. "But the premise of getting a calf ready to be weaned and moved to the feedyard stays the same. It's very much needed."

That's not likely to change, even as the industry continues to do so. The industry is not the same today as it was just 20 years ago, Dr. Griffin says. "I would speculate that less than 20 percent of cattle are going into the feedyard at 750 pounds. We're pulling lighter calves; we need to be more conscious of how carefully we handle them," he says. "We get them lighter and feed them longer. If you make a mistake on the front end, you'll pay for it longer."

For Mr. Wilburn, preconditioning is part of building lasting relationships with buyers by providing a quality product; he follows up to learn if they're satisfied and has repeat buyers for his calves. He tries to provide those calves with everything they need before they leave, and parasite control is an essential element of it. "If you expect to get a top calf, you've got to deworm them at least once," he says. "I don't know anything we can do to add pounds and get a healthy animal like the deworming process."