Nineteen percent of pro- include stomach worm, begin undergoing hypobiosis ducers used Barber’s pole worm and wire as they are acquired during exclusively in parasite man- worm. The adult worm, the autumn, September and agement. Eighty percent use found in the abomasum, is October. These larvae do some form of pasture rest 10 to 30 mm in length. not feed or lay eggs and do and/or rotation, 31 percent Females are very prolific, no damage to their hosts graze fields, and 7 percent each capable of producing as while in this state. However, are attempting to select many as 5,000 eggs daily. when the ewe or doe repro- and that are The life cycle (egg to mature duces, the worms receive sig- resistant to parasites. adult) is 17 to 21 days nals that it will soon be (Figure 1). Warm, moist soil spring and they resume Characterization surface conditions favor development. The lactating of propagation while hot, dry or ewe or doe is unable to rid Haemonchus extremely cold conditions herself of the now adult contortus are detrimental to larvae sur- worms and large numbers of Although numerous gas- vival. eggs are shed into the pas- tures. When the weather trointestinal are An important adaptation present, Haemonchus contor- warms up, larvae will be of Haemonchus contortus is waiting for the newborn as tus presents the greatest the ability to overwinter in concern in Texas sheep and well as the ewe or doe to the abomasum of its host in ingest them. goats. Common names for a dormant state known as Haemonchus contortus hypobiosis. Ingested larvae While most of the worms in hypobiosis survive, the larvae in the pastures die off, especially if it is a dry winter. Therefore, most of the worm population is in the host, not on the pasture as is the case during most of the year. The fact that lactat- ing ewes or does are unable to control adult parasite pop- ulations as well as dry ewes or does enables the worms to produce more eggs over a longer time span further con- taminating the pasture. The larvae develop more slowly in the late winter or early spring but survive until the really hot dry summer weather conditions desiccate them. Signs of include acute anemia, edema (bottle jaw), weak and listless behavior, and ultimately death. Diarrhea frequently occurs with heavy infesta- tions. Young and females 30 days either side of parturition are most vul- nerable.

Figure 1. Life cycle of Haemonchus Contortus Sources of 3. Ineffective compound. 4. Massive re-exposure. Anthelmintics available to Deworming animals and Resistance U.S. producers can be returning them to a heavi- products divided into three groups ly infested pasture is an available to Texas sheep and according to active ingre- exercise in futility. producers are limited in dient (Table 1). Since two Animals will immediately number. New product devel- of the groups contain only begin the reinfection opment, relative to the size of one compound, the con- process. Grazing manage- its market, is cost prohibi- cern of using an ineffec- ment (pasture rotation) is tive. Frequency of document- tive compound is potential- an integral part of an ed cases of resistant popula- ly more important in the internal parasite manage- tions is increasing. There- benzimidazole group. Use ment plan. Animals with fore, resistance management of an ineffective product is significant worm burdens warrants serious considera- a waste of producer’s can continue to shed tion. money and could lead to viable eggs for several the development of resis- hours or days after anthel- Several scenarios can tance. mintic administration. If result in resistance develop- possible, hold treated ani- Rotate products annually ment. These include: mals in the pen for 48 or until resistance develops. hours post-treatment and 1. Insufficient dose. The When rotating products, the then release them to an margin of safety for all appropriate rotation is uncontaminated pasture. approved products is wide, across classes of compounds at least twice the recom- (not within a class of com- mended dose. Therefore, pound). For example, rotate the dosage selected for all from a benzimidazole to animals should be appro- avermectin to imidothiazole, priate for the heaviest ani- not from thiabendazole to mal in that group fenbendazole to oxfendazole. (grouped by weight). Once an appropriate dose is selected, equipment should be checked periodi- Table 1. Anthelmintics available to U.S. cally to calibrate the sheep and goat producers. Only amount of product being three compounds are approved delivered. Delivery should for use in small . always be checked when Class of Compound Trade Name Efficacy against changing to a product of Active Ingredient Haemonchus contortus different consistency. Underdosing might save a Avermectin few cents in the short term ivermectin* Ivomec® +++ but can be quite costly Benzimidazoles should resistance develop. albendazole Valbazen® +++ 2. Inappropriate route of fenbendazole Safe-Guard®, ++ administration. Anthel- Panacur® mintics available to live- mebendazole Telmin® ++ stock producers may be oxfendazole Synanthic®, ++ delivered in one or more of ® the following forms: oral Benzelmin dose, subcutaneous injec- oxibendazole Anthelcide® ++ tion, pour-on, or feed addi- thiabendazole* TBZ® + tives. The appropriate Imidothiazole method for sheep and levamisole* Tramisol®, +++ goats is oral administra- ® tion of products designed Levasol for oral delivery. Follow *These products are approved for use in sheep and/or goats. label directions. Resistance greenup. The ideal treat- Tactical – when weather ment window for most of the conditions have been favor- Management state is December 15 - Feb- able for development of para- Strategies ruary 15. The primary tar- sites. Moisture (heavy dew gets of this mid-winter treat- or rain) must be present on Prevention, rather than ment are the hypobiotic lar- the soil surface to facilitate cure, is the philosophy used vae in the host. Therefore, a larvae movement from the in developing management product labeled for inhibited fecal pellet to the forage. programs for Haemonchus larvae (L stage) must be The purpose of the tactical contortus. It must be 4 used. treatment is to eliminate the assumed that this parasite active worms in the gut cannot be eradicated but can Another appropriate time before they have the opportu- be limited to the extent that for strategic treatment is nity to further contaminate it does not cause economic when animals are being the environment. Timing of loss to the producer. The fol- moved from a contaminated the tactical treatment may lowing strategies attempt to pasture to an almost para- then be based on 1) recent take advantage of livestock site-free pasture. A pasture precipitation and warm management and parasite can be considered relatively weather or, 2) increasing population dynamics when free of Haemonchus contor- fecal egg counts. implementing a management tus larvae if: 1) it has been plan. tilled since sheep and/or Fecal Egg Counts goats last occupied the pas- Strategic – when an ture or, 2) the pasture has Frequently during the anthelmintic is administered been completely vacant of spring, summer, and early while the parasite population sheep and/or goats for at fall, based on subjective is concentrated in the host, least three months during observations, internal para- transmission rate is very the spring/summer or early sites are cited as the cause slow and pasture contamina- fall or for at least six months of poor livestock perfor- tion is at an annual low. In during the fall and winter. mance. While parasites are Texas, the most appropriate For many sheep and goat frequently the culprit, other time of year for implement- operations with native range performance inhibitors do ing a strategic treatment is as a production base, defer- exist. Fecal egg counting is after the first hard killing ring pastures for this length a practical, cost-effective frost and before spring of time may not be feasible. diagnostic tool for determin-

Coccidia Nematodirus oocyst Haemonchus spathiger contortus Figure 2. Common parasite eggs and oocysts found in sheep and goat feces. ing parasite burden. This yields a less accurate ance of parasites is less procedure involves collecting assessment of parasite than later in the year a fresh fecal sample, mixing burdens. when nutrient require- 2 grams of the fecal material ments are lower. In 4. Early detection of resis- in a flotation solution and addition, resistance of tance development and examining a known quantity ewes or does to evaluation of anthelmintic of that solution under a Haemonchus contortus efficacy involves fecal col- microscope. For details on is weakened at the time lections and analysis 7 to the egg counting procedure, of kidding and during 10 days post-treatment. see TAEX leaflet L-5094, early lactation. Again, a minimum of 6 Monitoring Internal Parasite samples is suggested. ■ Many offspring are Infection in Small Rumi- Post-treatment samples weaned and sold by mid- nants. For reference, sketch- verify product efficacy. summer. Those remain- es showing the relative sizes ing in the flock have of eggs from commonly Results of the analysis increased in size and observed parasites are should be reported in eggs age such that they can shown in Figure 2. Several per gram of feces. Need for tolerate a larger para- points concerning fecal sam- treatment can be based on site burden. ple collection warrant fur- the “rules of thumb” listed ther consideration. in Table 2. ■ As a compliment to ani- mal management, anoth- 1. Fecal pellets may be taken These rules of thumb are er objective of these from the rectum or picked not etched in stone for every guidelines is to mini- up off the ground. An Texas sheep and goat pro- mize pasture contamina- excellent opportunity for ducer. They are merely tion (tactical treatment) sample collection is early benchmarks for producers to during the early part of in the morning as the ani- use in the development of the parasite season. The mals are leaving their bed- their specific IPM program. lower thresholds of 500 grounds. Fresh samples These rules are most applic- and 1,000 help to reduce are easily distinguished able to spring lambing/kid- such pasture contamina- from older, weathered ding operations. The rea- tion. droppings. soning behind these guide- lines includes: ■ Relative to parasite 2. Collect 8 to 10 warm, management, there is moist, soft pellets per sam- ■ During spring and early nothing significant ple and place them in a summer, nutrient about July 4 other than sealable plastic bag (to requirements for ewes it is a mid-summer date protect against dehydra- and does are high due that is easy to remem- tion). Samples should be to lactation, thus toler- ber. kept cool (<50o F ) until analysis. If immediate or same day analysis is not possible, samples may be Table 2. Treatment Thresholds for refrigerated (not frozen) Internal Parasites in Sheep for up to 72 hours. and Goats 3. Collect at least 6 individ- Time of Year Mature Yearlings and ual samples per parasite Animals Younger management unit prior to anthelmintic administra- Spring Greenup - July 4 1000 epg* 500 epg tion. Management units July 4 - First Frost 2000 epg 1000 epg might be pastures, flocks, *epg = eggs per gram of feces separate ranches, etc. Collection of a composite Egg counts equal to or above these levels warrant anthelmintic sample, while better than administration. no fecal egg count at all, The information given herein is for educational purposes only.Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Texas AgriLife Extension Service is implied.

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