by: Heather Smith Thomas

Part 2

Over the past few decades, stockmen have come to depend on deworming drugs for internal parasite control—to the point of overusing some of these drugs. Studies have shown that calves gain more weight if they are dewormed at strategic times during their first year of life. But this might not be the best plan, according to Dr. Louis Gasbarre (retired Research Leader for the Bovine Functional Genomics Laboratory of the Agricultural Research Service of the USDA, currently working in Wyoming as a consultant on cattle parasites).

If young calves can become exposed to just a few worms, they can start to develop immunity to those worms, but are not overwhelmed by large numbers of these parasites. “If you allow that immunity to build, then overall your herd will be in better shape. Low-level exposure in the calf is a good thing. Even though a producer's goal might be maximum growth in the calves, does he really need have to have that young calf growing at the absolute maximum potential? Even if a calf doesn't quite grow that fast, he will make up for it later. To allow that calf some limited exposure will enable him to be a much better, healthier animal in the future.”

A producer might say he/she doesn't care about that, since the calf will be sold before that point in time and the producer wants to get as many dollars as possible for that calf at weaning time. “That may work for awhile (heavy deworming of the calves at a young age, to get maximum response and gain), but then you are raising the likelihood that at some point the drugs won't work anymore,” explains Gasbarre.

“Producers need to consider a system in which they are using some type of management to keep transmission levels low, realizing that a small amount of transmission is ok,” he explains. Looking at this at herd level, the producer should accept a small amount of parasite transmission, and manage this in such a way that it will remain at a level that won't create significant impact on productivity. The key here is level of impact, rather than trying for no impact at all.

If the goal is to understand the biology of the worms, then the producer can worry about the small details, but if the goal is to produce healthy animals overall, Gasbarre's recommendation is to look at management as a whole, and try to manage overall transmission rates. “There are some slight differences you need to account for, but this should be looked at in the overall control rather than just protecting the calves better. If you keep transmission down to reasonable level all the time, you don't have to worry so much,” he says. The goal is to manage, not sterilize, the pasture. Don't choose an unattainable goal.

“Aside from temperature optimums for transmission, the main condition resulting in high transmission rates is moisture. If it gets dry, this does wonders for knocking down parasite transmission.”

At this point we still have some good deworming tools, with multiple classes of drugs. “This means we do have options if a problem arises. In general, we know a lot about what's out there, even though the parasites keep changing. We still have the ability to raise animals efficiently on pasture, but we do have to rethink the use of pour-ons so broadly. My advice is to use a drug that you can be absolutely sure about the dose you are giving to that animal, so you are not under-dosing or overdosing,” he says.

We don't have much problem with overdosing (except waste of money) because these drugs have a large margin of error, but if you under-dose this won't kill the worms and will lead to more drug resistance. “It's harder to provide the accurate blood level of drug with the pour-on, compared with an injectable or oral application,” he explains.

“There are many operations where it's not feasible to use anything but a pour-on, but they should think about it and determine if, in fact, they need to go that route. Right now the reason they do it is because it's easier and they be doing two things at once—such as treat for lice as well as worms,” he says. But if worms are a major concern, it might be better to concentrate on the best way and timing to kill the worms.

“Some people will tell you that the pour-ons are as effective as any other method, but if you go back to the scientific literature you will see that they are not always what they are cracked up to be. In some cases (as when trying to get lice) they are appropriate to use, but in other cases they may not be. If your goal is to have good parasite control, you should do what's best for a particular parasite and not just what happens to be easiest to do, that day,” says Gasbarre.

“Pour-ons are a fact of life and will always be available because they do have some usefulness, but we should be making sure we are using the right practice at a given time,” he explains. The main point to understand is that just because something was working in the past does not mean that it always will. We need to practice good management and be prepared for and receptive to change.

“The biggest problem I see in the industry now is that we've become rigid in our thinking, because some things have worked for us for 30 or 40 years, and a lot of people don't like change.” If people are comfortable with something, they often don't look beyond that.

“They need to look at this from a business standpoint. The successful businesses are those that adapt and change to meet the needs and production demands. This is where we are now—at a point where change is happening. The successful producers will be the ones who can see this and make the change, rather than blindly going along with a certain practice because it always worked for them in the past. Producers need to be good businessmen, first,” he says.

“We are in a period of change, regarding parasite control, and it took us 40 years to get here. It's here now, so producers need to be receptive to it, and checking behind themselves whenever they deworm their animals. They also could benefit from checking with experts in the field, saying this is where I live, these are my environmental conditions, these are my goals, and what would you suggest?”

When someone calls Gasbarre to ask when they should treat their animals, he first wants some details about their particular operation. “If you ask a consultant when you should treat your animals and he starts giving you a program without assessing your situation, beware. That person is obviously reading something out of a book and it may not fit your operation.”

Some producers don't want to be bothered with providing the necessary inputs to figure this out. “Would those same people do that in terms of what the cattle markets are like—wanting to know which day, every year, they should sell their calves, or cull cows? The market might be better a different day! You need to understand the entire picture of what's happening, to come up with proper timing—whether it's selling your cattle, or deworming them. To always treat them on the first day of March is just as silly as saying that historically markets are high the first of March so that's when you should sell all your calves. People need to contact experts and get an understanding of what to expect for deworming in their area, and then they need to manage with an eye on keeping track on how effective their treatments actually are.”

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