The importance of controlling parasites

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Deworming calves may be the most cost-effective management practice around: it results in healthier calves with healthier immune systems, weight gains that provide return on investment, and cleaner pastures.

Parasites have many effects on their host, all of them negative. Some of the worst effects relate to the function of the host’s immune system and its ability to respond to vaccines. 

Parasites can cause varying degrees of anemia, and lower white-cell counts mean a lower response to vaccines. Anemic animals also have lowered red-cell counts, and their ability to transport oxygen is impaired. “If an animal is parasitized, it won’t respond to vaccine antigens as well, and desired immune response to the vaccine is the reason we go to the effort of vaccination,” says Bill Burdett, technical services veterinarian with Intervet. “We want maximum antigen response. We want the animal’s lymphocytes, which are part of the white blood cells, to respond optimally.”

There is also a stress factor to consider. “Parasites tend to stress an animal. A stressed animal doesn’t respond as well to vaccines,” Dr. Burdett says.

   When the immune system is stressed, even dewormers won’t work as well as they should, so a vicious cycle begins. “If you’re controlling parasites, the immune system is more stable,” says Bill Clymer, a parasitologist with Fort Dodge Animal Health. “An immunosuppressed calf will get even more parasites, because he is more susceptible.”

Decreasing the effectiveness of the immune system is part of a parasite’s modus operandi. “Here’s a foreign animal invading your body and trying to survive,” says James Hawkins, associate director of veterinary professional services for Merial. “He’s trying to evade your immune response. It seems a likely strategy for him to try to suppress your immune system.” If the animal is faced with another pathogen, its immune response will be less than optimal.

He cites a study at Auburn University in which calves were given brown stomach worms. Then some of the calves were dewormed, and some were not; all were vaccinated for IBR and blackleg. In the dewormed calves, the antibody responses were higher; their cell-mediated immune response was higher, too. In other words, their immune systems responded more strongly in every way possible.

So, deworming at the same time as vaccinating does help with the response to those vaccines, Dr. Hawkins says. “Deworming two to six weeks prior to vaccination is best, but if you have wormy calves that need vaccination, you can’t afford to wait.”

Performance costs
As with immunity, worms negatively impact performance in several ways. First, they compete with the host for nutrients. “They also secrete an enzyme that affects the appetite of the animals. So they are losing the nutrient value and not eating as much to start with,” Dr. Clymer says.

In a study of four pour-on endectocides, all products resulted in increased gain; there was a 57-pound difference between animals treated with the most effective product and the untreated controls, says Dr. Clymer. If the producer of those calves had failed to deworm, his calves would have been significantly lighter and, at today’s market, been worth close to $70 less per head.

That’s why improved production, both in weight gain and milk production, is the major reason to deworm. “They’re going to eat more and they’re going to gain more,” Dr. Hawkins says. “Whether they’re eating grass or a concentrate ration, improved appetite is something we can always count on any time you deworm. If they’re parasitized to the point that they are sick, the performance difference can be huge. But even if they’re gaining a pound a day, deworming them can add a quarter to a half pound a day  —  even if they have relatively low worm burdens and they don’t act or look sick.”

Trials show that deworming can also improve carcass quality on every parameter measured; this is an area still being researched. “We’re getting some information on beef quality,” Dr. Clymer says. “There’s a relationship to quality grade and animals that have been dewormed. We have seen an improvement, but we’re not sure exactly what the relationship is.”

Preconditioning
As more and more research shows the importance of deworming, more preconditioning programs are emphasizing it. “In my opinion, it’s important to deworm at the time of preconditioning  —  optimally, it would actually be two weeks before the vaccines are given. Logistically, few people can do that, unless they deworm on grass using a feed grade dewormer through the mineral or use a block or pellets,” Dr. Burdett says.

Dr. Burdett recommends deworming cow herds, too. “At preg check in the fall, make sure she gets effectively dewormed,” he says. “Regardless of technique, do an effective job of deworming in the fall, then deworm both calves and cows again about six weeks after grass turnout.” The reason: cows will pick up larvae and eggs that overwintered on the pasture. Killing those larvae in the cows before they mature and start laying eggs will prevent them from recontaminating the pasture, and that will help keep the number of eggs in the cows and calves to a minimum.

Treating the cows will also protect the investment of treating the calves. “Some producers start preconditioning several weeks before weaning,” Dr. Clymer says. “They may pour them and put them back with their mommas, but they didn’t treat their mommas. The calves may become re-infested with both internal and external parasites from their mothers.”

Whether or not a producer retains ownership into the feedlot, they may reap the benefit of dewormed calves. “The name preconditioning, in itself, would suggest the reason you do it is to make sure they’re in better condition. The number one reason is to improve health,” Dr. Hawkins says. “The other reason is if you hold these cattle 45 days or more, you can put considerable amount of weight on in the meantime.”

In the past, the focus of preconditioning has largely been on vaccinating and reducing stress. “Those are important, but it hasn’t always been recognized that deworming is as important as it is,” Dr. Hawkins says. “It should be an integral part of the entire process, no matter where you are or what time of year it is.” That will only become more important to producers who sell calves as the industry evolves. “A lot of feedyards and buyers are starting to look specifically at how animals are responding and performing. With animal ID and source verification, they are getting a handle on which ones do well and which don’t,” Dr. Hawkins says.

Spring deworming
The aim of deworming is to control parasites, not to eliminate them  —   which would be impossible in any case. Parasites are always trying to get into a herd through three sources: the soil, which can be laden with larvae burrowing into the ground in the dry season, the cow and the calf itself. “The calf becomes a multiplier, not just a source,” says Mike Lathrop, who covers veterinary operations in the western cow-calf division of Pfizer Inc. “He has no natural immunity to them.”

A good time to interrupt the parasites’ cycle comes prior to moving cattle onto a new pasture. “We think of fresh, green pastures as clean,” Dr. Lathrop says. But that is not the case, especially if those pastures are used every year. “There are more and more studies about parasitism that are conducted, not in the wet southeast, but in the dry rangeland areas,” Dr. Lathrop says.

Spring deworming is not only strategically important for cleaning up pastures, it is another opportunity for producers to benefit from extra gain, no matter their marketing methods; they will have time to realize the returns. “Many cow-calf producers are going to wean calves and never see the impact of fall deworming,” Dr. Lathrop says. “Spring deworming is where they’ll see the benefits.”

In a study that showed the benefits of deworming at or near turnout, herds were treated at 0 and 10 weeks, at 3 and 10 weeks or not treated at all. The herd treated at 3 and 10 weeks showed a weight advantage of 43.56 pounds over the control group; the 0- and 10-week group showed a 32.66-pound advantage.

Deworming in the spring may also provide an opportunity to get back the gain lost in a situation where implants cannot be used. “With deworming programs, here’s a product you can use in that natural program; here’s an opportunity to replace that lost poundage,” Dr. Lathrop says.

“If you only deworm once, the single biggest return is on spring deworming for the cow and calf at 2 months old,” Dr. Clymer says. “This also applies with fall calving; you can expect an
extra boost in gain by treating the cow and calf.” One dry year on his own herd near Amarillo, Texas, he dewormed only half of the cows and their calves in the spring. He ended up with 35-pound lighter calves in the untreated half.

“With spring deworming of the cow and calf, there are a number of studies in which we’ve doubled our investment in weight gain on the calves,” Dr. Clymer says. Cow weight gain, of course, is not an issue, but egg shed is. One cow-calf pair with a light to moderate infestation can shed in the neighborhood of 51 million eggs over a grazing season. 



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