by: Heather Smith Thomas

Part 1

Internal parasites (stomach and intestinal worms) rob cattle of important nutrients, reducing growth rate and weight gains in young animals and hindering optimum production in all classes of cattle. Heavy infestations create health problems. Worms are an added stress and can make the host animal more vulnerable to disease. Deworming cattle at the proper times of year, at the most appropriate stage in the life cycle of a certain parasite to eliminate egg-laying adults in the tract—to most effectively minimize re-contamination of pasture with worm eggs--can keep reinfection to a low level.

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) says producers should first define their goals and needs. “What has happened over the past few years—the development of drug resistance in some of the worm populations—has shown us the fallacy of thinking we can completely control the parasites,” he says.

“In the past we thought we could hit the parasites as many times as we want and then walk away and say we did a good job in parasite control. The parasites have tremendous potential for change. Prior to the 1980's producers controlled parasites with good management. They rotated different classes of livestock on various pastures, watched the animals, tried not to overstock pastures, etc. Our close attention to management went by the wayside when the new wonder drugs became available, and we thought we didn't need to do anything except deworm the animals,” he says.

“As the dewormers got cheaper, and easier to use, the producers and the people making the recommendations for deworming were all lulled into a false sense of security because the drugs are so good,” explains Gasbarre.

Today, a producer first needs to decide on certain goals. “A stocker operation will have different goals than a cow-calf operation, which are also different from a feedlot situation. If you pasture cattle, you always have to deal with a parasite population. That's a fact of life. Our priorities should be to meet our production goals, but at the same time develop a system that will be sustainable over time.” If we just keep using these really great tools indiscriminately, we may lose the efficacy of these tools.

“These drugs are very powerful, and we need them in order to manage parasites successfully. We want to maintain that edge,” says Gasbarre. We should not use them without considering the future. Knowing that overuse of these drugs today will cause us problems later, we need to be conscientious. If we have the attitude that we need them right now, with no thought for the future, eventually our cattle operation may not be sustainable.

“The first thing any producer needs to define is his/her goals for production, but not try for an unnecessary level of production. Then think about the best way to meet those goals in terms of coming up with a system that will give what we need, but not more than that. This can be difficult, but there are many people who can serve as resources for what we need to know. The important thing for a producer to understand is what's happening on the pastures, the makeup of parasites and the optimal times to treat cattle to get the desired effect, while at the same time not over-treating,” he explains.

“One thing we need to do now, which we never had to do before, is check after deworming—to make sure the treatment works. We need to monitor the animals after treatment. The animals may ‘slick up' but we need more than that to go on, such as growth parameters, and checking to see if those parameters are within your goals as a producer,” says Gasbarre.

Some people think they don't have time to do this, but they won't stay in business very long if they do have a resistance problem and the drugs aren't working. They are wasting money on the drugs and not helping the cattle. “You wouldn't buy a product of any other kind and not make sure you got your money's worth. So you need to take a little time and get some kind of measure of effectiveness of that treatment. And if it's not what you'd expect, then you should contact someone to see what you need to do—and rethink that treatment.”

People are now using combinations of drugs, to maintain efficacy in treatments. “Using multiple classes of drugs, if the single classes aren't working, still gives good results. People ask why these drugs aren't available in a combination product. The answer is that the FDA hasn't felt this is something they should consider or license. Their idea was that if a drug doesn't routinely work, they wouldn't license it. This is a good approach, but maybe too idealistic, by ignoring the ability of these parasites to change,” says Gasbarre.

“Now that the worms are changing, what do we do? Must we try to come up with a totally new class of drugs? We'll probably have to wait a long time before this happens, so what do we do in the meantime? I think the FDA is beginning to change their ideas on this, and may look questions surrounding combination drugs. But for the present, we have to treat with two different products in some instances,” he says.

Regarding the best times to treat, this depends on what's happening on the individual pasture at a given time. It will vary from one location to another, and also with the seasons, weather and different environmental conditions. “There will be some generalities, however, that can be given for various locations. We can focus on those times for treatment, but it has to be within the concept of meeting the producer's goals, and not doing it simply because somebody else is doing it then,” he explains.

In young stock you might be targeting some different worms than what you'd be worrying about in adult cattle. “The immune system in cattle has had a long time to co-evolve with the worms. It generally does a pretty good job of keeping worm numbers down to an insignificant (minimal damage) level, compared to that of small ruminants like sheep and goats,” says Gasbarre. Cattle are very good at developing some immunity to the various internal parasites after coming into contact with them.

“By contrast, sheep and goats may have severe helminth problems, even in adult animals. Cattle have evolved a fairly efficient immune response to many of the parasites. So if transmission levels remain low and you have good pasture management (not overstocking/overgrazing pastures), the cattle generally will have a relatively small number of worms, especially if the cattle are on a good plane of nutrition,” he says.

“If you have consistently managed correctly—with an idea of what parasites exist on your pastures and you understand the transmission time, in your location, and use the deworming drugs judiciously--you likely don't need to worry too much about the little things. The transmission won't become that severe,” he says. It's always a numbers game. Once the worms get the upper hand, however, it's a lot harder to deal with.

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