by: Richard M. Hopper
DVM, MSU-CVM, Pathology & Population Medicine

The middle of the summer is traditionally a time when producers don't have to focus a lot of time on the cowherd. With the exception of fly control and the occasional problem with a toxic or noxious plant we can tend to ignore things a little. However the middle of the summer may be one of the best times to deworm your cattle. In this article I will provide you a brief overview of strategic deworming, which is just a term coined several years ago to reflect a deworming plan that takes into account pasture worm burdens, worm life cycles, climate conditions, and treatment timing to increase your economic return from this important health management tool.

Cattle producers tend to deworm cattle at times based on convenience and tradition. Anthelmintics (dewormers) are usually selected based on cost, perceived effectiveness, or many times convenience of administration. Knowledge of parasite life cycles, coupled with the effectiveness of our modern anthelmintics makes it possible for producers with the assistance of their veterinarian to deworm their cattle more effectively. Deworming cattle even in a haphazard way is usually cost effective from the standpoint of a cost to performance return, but to maximize returns from your deworming program you must utilize a strategic deworming program.

Strategic deworming involves developing and implementing a long-term plan in which you and your veterinarian base product selection, time of deworming, and interval between deworming on the pasture environment, the season or climate, and the cow herd's stage of the production cycle. Therefore a strategic deworming program is often or in fact usually different among farms. Since at any given time 95 percent of the parasites are on the pasture and only five percent are in your cattle, an important aspect of a strategic deworming program is timing administration of the anthelmintic in an attempt to break the life cycle of the parasites and decrease pasture load. As you might imagine if this is done successfully over several years the parasite load on a pasture can be significantly reduced. This situation will not allow you to curtail or decrease the frequency of your deworming program, but it will decrease the loss of productivity that parasites cause "in between" dewormings. Consider the situation that occurs with a random deworming. The cattle are "purged" of the worms but because they are continually exposed they become reinfected and within three to four weeks begin shedding more worm eggs on the pasture. Does this mean random deworming is not effective? No, as I stated earlier it is cost effective and it does remove the worms from the cow albeit temporary. It is just that repeated deworming in the spring when grass is lush and the climate is most conducive to parasite build-up on the pastures is most effective in economically controlling parasites.

I mentioned several factors that should be considered in developing our deworming program. How does each impact parasite control? The season of the year has the most obvious impact. Despite what most people think most cattle intestinal worms can survive the winter even in the northern states much less Mississippi. We do however get good response from our deworming efforts that are timed after a hard frost or in mid-winter because the worms do not multiply on the pastures as they do in the spring. The lush pastures we have in the spring coupled with moderate temperatures however provide perfect conditions for worm population build-up. This is when repeated deworming treatments may be cost effective. Also remember the hot, dry weather (pasture brown-out) of July & August is the most detrimental environment or climate for worm survival. If we can "clean-out" the cows at that time they can usually stay relatively worm free for a couple months. Also the production phase or age of the cattle is a factor. Calves have little or no immunity to parasites and cows that are pregnant, in poor condition, or otherwise stressed have lowered resistance as well.

In conclusion we all know that what the companies that sell deworming products say is true. "Deworming pays." However how we do it determines the economic benefit we receive.

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