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Working Ranch April/May 2016

Cowboy Dictionary — refugia EDITOR: A few years back we did one of these dictionary boxes for the word anthelmintic (the ‘th’ is pronounced ‘t’). Well, let’s refresh, because that word is in this article a few times (remember… it means ‘parasite control product’ like dewormer). Here’s another word this ol’ cowboy never heard before… refugia (reh-fyoo-gee-ah). The root word is “refuge”, so let’s start there. Try hard to follow along, it took me a couple of reads to get it. more time to develop resistance. The more generations of worms you have in the population, then the more exposed to dewormers, and the increased likelihood of resistance.” This is a message ranchers in the southeastern part of the country may not want to hear. Louisiana State University’s Assistant Professor in Food Animal Medicine and Surgery Chance Armstrong conducts most of his research on infectious causes of infertility in cattle. He grew up on a cow calf ranch in Alabama and worked in a large animal practice in south Florida after completing his doctorate of veterinary medicine at Auburn University. He later returned to Auburn to specialize in large animal reproduction and then joined the faculty at LSU. Armstrong says parasite control is a very complex subject, particularly in the southeastern United States where climate and environmental conditions are ideal for parasites to thrive. Armstrong says there is documented anthelmintic (parasite control product) resistance to all commercially available products in every important cattle parasite worldwide. He says cattlemen need a basic understanding of parasite biology and control measures so they can work with their veterinarian to develop parasite control programs. The goals, he says, is to balance the short term economic benefi ts of deworming with the long term impact of anthelmintic use on resistance. Armstrong says diagnostic testing is required to determine the existence and extent of parasite problems and anthelmintic resistance on each ranch. Quantitative fecal egg counts are essential in determining the magnitude of parasite problems, and the fecal egg count reduction test (FECRT) can be used to estimate anthelmintic resistance. “One of the key concepts in slowing down the development of resistance is the maintenance of refugia,” Armstrong says. “Parasites in refugia do not have genes for anthelmintic resistance, they are still susceptible to anthelmintics. The more refugia in a population, the more the resistance genes in a population are diluted and the more effective anthelmintics will be.” Armstrong suggests the quickest way to get widespread anthelmintic resistance is to deworm an entire group of cattle and then put them on a clean pasture. This eliminates the susceptible parasites in the animal and all that are left are resistant parasites to reproduce and pass on resistant genes to their offspring. The results are a lack of susceptible parasites to dilute the resistant population of parasites in the animal and on the pasture. This is an essential lack of refugia. He says it is important to get the advice of a local veterinarian on which products they should be using because the recommendation does vary based on the region, the challenge, and the time of year. A working relationship with a local veterinarian who is familiar with the operation can also assist ranchers in fi nding a balance between keeping SOURCE: FDA Center for Veterinary Medicine Refugia is the proportion of the total parasite population that is not selected for antiparasitic drug treatment—essentially, those parasites that are in “refuge” from the drug. Therefore, there’s no selection pressure on these parasites to develop resistance. Refugia (Editor: the strategy of refugia, they mean…) maintains a proportion of susceptible parasites on the ranch and includes: • Parasites in untreated animals, called hostbased refugia. • Eggs and larvae already on the pasture when the animals are treated, called environmental refugia. • Life stages of the parasite that are unaffected by drug treatment, such as some larval stages. Example: I am going to deworm the WR calves this fall, but I’ve decided I’m going to pursue a refugia strategy. The fi rst thing I’m going to do is consult my veterinarian because they know the calves and the outfi t, and they know what specifi c parasite problems we are challenged with. The veterinarian will come up with; A) the scope of the parasite challenge through diagnostic testing and fecal egg count reduction testing; B) the anthelmintic to be used, and; C) a strategy for utilizing a refugia program, which may include deworming 90% of the calves with one product, and the remaining 10% with an entirely different one. Makes sense, now that I think about it. ASK YOUR VETERINARIAN ABOUT A refugia STRATEGY THAT MAY WORK FOR YOUR OUTFIT Chance L. Armstrong, DVM, Assistant Professor-Food Animal Health Management, Department of Veterinary Clinical Sciences at Louisiana State University. APRIL / MAY 2016 I WORKING RANCH I 45


Working Ranch April/May 2016
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