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=20
Internal & External =
Parasites of=20
Goats
Unit ObjectiveAfter completion of this module of instruction the = producer=20 should be able to observe goat=92s symptoms for possible = infestation of=20 parasites by personal observations and by using the FAMACHA=A9 Eye = Color=20 Chart. The producer should be able to identify specific parasite = problems=20 within the goat herd and develop a management/control program for=20 controlling parasites within the goat herd. The producer should be = able to=20 complete all assignments with 100% accuracy and score a minimum of = 85% on=20 the module test. Specific ObjectivesAfter completion of this instructional module the producer = should be=20 able to:
Module ContentsEffects on Herd = ProductionParasitism, and gastrointestinal nematode = parasitism in=20 particular, is arguably the most serious constraint affecting = small=20 ruminant production world-wide. Economic losses are caused by = decreased=20 production, cost of prevention, cost of treatment, and the death = of=20 infected animals. It is difficult by any form of major survey or = other=20 estimation to establish precise figures on losses incurred in = production=20 from infection and disease. Even minimal accuracy of loss = estimates is=20 difficult because production diseases or disorders may result from = interaction with nutritional and environmental stresses, = management=20 methods, concurrent diseases, genetic predispositions, or other = factors.=20 Periodic reports on such losses from governmental agencies and = others,=20 always range into millions of dollars per year and include all = phases of=20 production. Problems with nematode parasitism are often = classified as=20 production disease (i.e. chronic subclinical condition affecting=20 productivity such as weight loss, reduced weight gain, = reproductive=20 inefficiency, etc.). A summary of diagnostic laboratory necropsies = in=20 Kentucky showed that worms accounted for 90% of the deaths in 428 = goats=20 submitted. Since goats and sheep share the same parasites, a = recent=20 publication of the USDA-APHIS-VS provided some data on the = magnitude of=20 the problem. Sixty-two percent of 5,174 sheep producers surveyed = in the=20 United States identified stomach/intestinal nematodes as a major = concern.=20 These losses were compounded in the southeastern region (Alabama,=20 Arkansas, Georgia, Florida, Kentucky, Louisiana, Mississippi, = Maryland,=20 North Carolina, South Carolina, Tennessee, Virginia, and West = Virginia) of=20 the U.S. because climatic conditions are generally more conducive = to the=20 growth and establishment of large nematode parasite populations.=20 Seventy-five percent of 467 sheep producers surveyed in this = region=20 identified stomach/intestinal nematodes as a major concern. There is no similar data for goats, but it can be = expected=20 to be relatively the same. However, it should be noted here that = is more=20 so the case when goats are managed as grazers. When goats are = managed as=20 browsers, exposure to nematode parasites is reduced and = subsequently the=20 effects are not as severe. The nematode of particular concern is = the=20 Barber-pole worm (Haemonchus contortus). The tremendous=20 egg-laying capacity of H. contortus is maintained by = feeding on=20 blood by both immature and mature stages. Severe blood loss can = occur,=20 resulting in anemia, loss of appetite, depression, loss of = condition, and=20 eventual death. Other worms contribute to =91production disease=92 = as they=20 usually do not kill, but affect the animal=92s ability to increase = and/or=20 maintain production (i.e. weight, reproduction, etc.). External parasites, for the most part, are a = nuisance and=20 can cause reduced weight gain and weight loss simply because the = animal=20 spends more time and energy combating them than feeding. Physical = injury=20 occurs when irritation and scratching result in open wounds that = then can=20 become infected or subject to infestation with fly larvae. Nutrition InteractionThe effects of parasitic infection can be = influenced by the=20 nutritional status of the host. It is well known that well-fed = animals can=20 better withstand parasite infection than animals on an inadequate = diet. It=20 is also true that parasites interfere with the ability of the host = to=20 utilize nutrients efficiently. Therefore, it is important to = understand=20 this see-saw effect. The better an animal is fed the better it is = able to=20 tolerate increasing infection levels, but eventually a point may = be=20 reached, depending on the worms and conditions involved, where = parasitism=20 overwhelms the host=92s ability to function properly. To satisfy = body=20 demands, most nutrients are absorbed from the gut during digestion = and=20 additional nutrients are available as needed from body reserves. = The term=20 nutrient partitioning refers to the process of directing the flow = of=20 nutrients to where they are most needed at the current time. = Depending on=20 the host=92s age and sex, season of the year and exposure to = various=20 potential infectious (parasitic and otherwise) agents, nutrients = are=20 partitioned for growth, breeding, pregnancy, lactation, immunity, = etc. The=20 ability of the host to maintain a proper balance of this = partitioning=20 ensures that nutrients are used appropriately. For example, as=20 gastrointestinal worm infection increases, more damage is done to = the=20 mucosa which will result in reduced absorption of nutrients, thus = making=20 the host utilize more stored body reserves. In addition, proteins = are the=20 building blocks of the host=92s immune system. So, as proteins are = made less=20 available, the host=92s immune function is compromised and it = becomes more=20 susceptible to subsequent infection. Overall, the net result of = inadequate=20 feeding, for the conditions encountered, will be loss of = productivity=20 unless the balance is restored. Internal ParasitesGastrointestinal nematodes = (worms) Although there are a number of worms found in = goats, only=20 the predominant and usually the most pathogenic ones will be=20 discussed. Before control measures can be considered, it is = important=20 to understand some aspects of the life cycle of these worms. The = life=20 cycle consists of part of their life being spent inside the goat = and part=20 of their life on the pasture (Figure 1).
The infective larvae have a protective sheath = making them=20 relatively resistant to adverse environmental conditions and can = survive=20 for months, thus extending transmission potential. As long as the=20 temperature and moisture conditions remain warm and wet = (especially=20 following periods of substantial rainfall), development and = survival=20 continues and pasture contamination accumulates, but if the = temperature=20 gets too hot/cold and/or the moisture conditions become dry, = development=20 and survival are threatened and pasture contamination dissipates.=20 Transmission of parasites can be reduced by implementing control = measures=20 to eliminate the worms from the goat (deworming) and/or reducing = the=20 chances that infective larvae have to reinfect the goat = (management).=20 Depending on the worm species, the time of the year that is most = favorable=20 for transmission varies. This will be addressed below. Another way to look at the life cycle is in four = phases.=20 Phase 1 is the Parasitic Phase which is the interaction between = the goat=20 and the parasite. Phase 2 is the Contamination Phase which is the = result=20 of eggs that are passed in the feces during defecation. Phase 3 is = the=20 Free-Living Phase when larval stages develop and survive. Phase 4 = is the=20 Infection Phase when available infective larvae are consumed = during=20 grazing. There are a number of factors that affect what happens = and=20 influences control strategies during each of these phases (Figure = 3).
During Phase 1, the parasite has to develop and = survive in=20 the host. After ingestion, infective larvae lose their protective = sheath=20 and invade the mucosa (lining) of the abomasum, small intestine or = large=20 intestine depending on what worm is involved. While in the mucosa, = larvae=20 develop to the next larval stage and then return to the surface of = the gut=20 mucosa where they become adult worms. The goats major defense = mechanism=20 against parasites is the immune system. When infectious agents = enter the=20 body, the immune system reacts through a series of activities that = mobilize various components (antibodies, killer cells, etc.) that = then=20 attack and kill the invaders. These components act on the larval = stages in=20 the mucosa and the adults. How strong the immune response is = depends on=20 several factors. The immune system has to mature with age, = therefore,=20 young animals are relatively susceptible to infection and become = more=20 resistant with age. So, young animals usually harbor the heaviest=20 infection levels and suffer the most severe consequences. Adult = animals=20 have developed stronger immunity and harbor lower infection = levels. One=20 way infection level is measured is by quantifying the number of = eggs being=20 passed in the feces. So, relatively high and low egg counts are = usually=20 seen in young and adult animals, respectively. Young animals are = more=20 subject to clinical disease where signs of infection (diarrhea, = rough hair=20 coat, anemia, weigh loss, bottle jaw, etc.) are seen. In older = animals,=20 infection usually becomes more subclinical where the only subtle = sign may=20 be reduced weight gain. However, nutrition (as mentioned above) = and/or=20 stress can alter a host=92s immune competence. Under poor = nutrition and/or=20 stressful conditions, the immune system loses some effectiveness = and can=20 not respond adequately. Therefore, no matter what the age of the = animal,=20 the effects of infection will become worse. The prepatent period = of most=20 worms is about 3 weeks, but this period can be extended for worms = that=20 have the capability to enter a period of delayed or arrested = development=20 called hypobiosis. This occurs during the season of the year when = the=20 environmental conditions are unfavorable for development and = survival of=20 the free-living larval stages. In warm climates, this happens = either=20 during summer or winter depending on the worm. In colder climates, = all=20 worms capable of hypobiosis will arrest in the winter. Phase 2- Contamination = Phase The magnitude of pasture contamination during = Phase 2 is=20 affected mainly by stocking rate (number of animals per grazing = area), age=20 of the animals, season of the year and hypobiosis. The = higher/lower the=20 stocking rate, the more/less feces are deposited on the grazing = area, thus=20 more/fewer eggs. More eggs are also passed from young vs. older = animals.=20 Most worms have a definite seasonality, so during their = =91season,=92 more=20 eggs are produced and passed. Of particular note in small = ruminants, is a=20 phenomena called the peri-parturient rise (PPR) in fecal egg = output. This=20 occurs at or around parturition (kidding) and extends through most = of the=20 lactation period. Because parturition and lactation are stressful=20 conditions, the dam=92s immune system is compromised. Furthermore, = nutrients=20 are partitioned preferentially to support mammary and fetal = development=20 and then lactation, which also decreases the animals=92 ability to = generate=20 an effective immune response to worm infection. This allows the = existing=20 female worms to increase the number of eggs laid, thus increasing = the=20 number of eggs deposited in the feces. If a worm species undergoes = hypobiosis, the development time to the adult stage is extended by = several=20 months. This will result in fewer adult worms over time and fewer = eggs=20 deposited in feces. However, when these hypobiotic larvae resume=20 development, massive numbers become mature adults over a short = period of=20 time and the resultant egg production and deposition in the feces = can be=20 very high as well as having severe adverse effects on the = animal. Development and survival of the free-living stages = during=20 Phase 3 depends on prevailing environmental (temperature and = moisture) and=20 nutritional (oxygen and energy) conditions. Initially, the first = stage=20 larvae develops in the egg which then hatches, and then = development and=20 survival to second-stage and finally third-stage (infective) = larvae occurs=20 within the fecal mass. The first- and second-stage larvae are = unprotected=20 and need oxygen and energy (feed on nutrients and microorganisms) = to grow.=20 The infective larvae is enclosed in a protective sheath and does = not feed.=20 Temperatures conducive for normal development and survival are = between=20 65-85EF. The lower or higher the temperature gets, development and = survival is reduced. Moisture is also crucial for development and=20 survival. Because the initial development and survival occurs = within=20 feces, moisture is usually adequate to complete development to the = infective larvae; however, if the feces dries out quickly, due to = high=20 temperatures and/or physical disruption, the first- and = second-stage=20 larvae are susceptible to dessication and will die. If feces = remain=20 intact, retain some moisture and do not get too hot or too cold, = infective=20 larvae may remain alive for months. A moisture medium (rain/dew) = is=20 necessary for infective larvae to migrate out of feces, and they = are=20 relatively resistant to environmental conditions encountered due = to their=20 protective sheath. Temperature is usually the only factor that may = adversely affect the infective larvae. Generally, infective larvae = can=20 survive very low temperatures, but may die off during hard = freezes.=20 Sustained temperatures above 95EF are usually lethal. The moisture = conditions at ground level under forage cover usually is adequate = for=20 infective larvae to move around and survive. Since they don=92t = feed, their=20 length of survival depends on how fast they use up their energy = reserves.=20 So, the hotter it is, the faster they move and use up energy = stores and=20 survival is shorter. Eventually, infective larvae move up and down = the=20 forage when there is a moisture medium (i.e. advancing and = receding dew).=20 Rain also provides a moisture medium for larval movement on = forage. For=20 the most part, infective larvae do not move much past 12-24 in = from feces=20 or 2-3 in up the forage. So, the lower the animals graze and the = closer to=20 feces, consumption of infective larvae is increased and vice = versa. Phase 4 is affected again by stocking rate in 2 = ways. If the=20 same animals are grazing, the stocking rate determines how many = eggs=20 initially contaminated (Phase 2) the pasture and, consequently, = how many=20 infective larvae will be available for consumption. If the initial = contaminating animals are removed and replaced by new animals, the = new=20 stocking rate will determine the level of exposure each animal has = to=20 infective larvae during grazing, i.e. the higher the stocking = rate, the=20 more chance of exposure and vice versa. It is well known that = grazing=20 animals usually do not graze close to feces so the further the = distance=20 between fecal deposits, exposure is reduced. Eventually feces=20 disintegrate, forage grows well with the fertilization and animals = will=20 graze over the area where exposure can be high. Natural sources of = water,=20 such as streams, ponds or lakes provide moisture along the banks = where=20 forage can grow readily. When animals congregate to drink and = consume the=20 attractive forage, defecation in these areas usually leads to = increased=20 contamination and eventually more infective larvae. The same can = be said=20 for areas where supplements, especially hay, are fed on the ground = if=20 conditions are right for development and survival of the = free-living=20 stages. Similarly, trees provide an area for animal congregation = and=20 shade. Under all these situations, essentially a high stocking = rate has=20 been artificially created in a relatively small area where forage = is kept=20 closely grazed. Haemonchus contortus=20 (Barberpole worm)
Generally speaking, H. contortus = transmission and=20 infection is at the lowest level during the winter. Transmission = and=20 infection increases with the warmer temperatures and increasing = moisture=20 during the spring and peaks during the summer. As temperatures and = moisture dissipate during the fall, transmission and infection = decreases.=20 Hypobiosis has not been observed to occur to any great extent in = the SE US=20 because the life cycle can be maintained year around, but it does = occur in=20 more northern/western temperate (cold/dry) regions of the US.
Telodorsagia=20 (Ostertagia) circumcincta (Brown stomach worm) The other abomasal worm of importance is = Telodorsagia=20 circumcincta which is smaller than H. contortus and = is not=20 readily visible since it is about as big as an eyelash. These = worms feed=20 mostly on nutrients in mucous and do not feed on blood, per se, = but can=20 ingest some blood if present. Female worms do not produce as many = eggs as=20 H. contortus. Infection causes direct damage to the = stomach=20 lining thereby interfering with digestion and appetite. Infection = is=20 usually considered a production disease as animals do not grow = very well.=20 However, under very high infection conditions, death can result. = When=20 infections reach levels that cause disease to be seen, the primary = symptom=20 is diarrhea. This worm thrives in cooler wet environmental = conditions=20 which are encountered in the more temperate regions of the US = (excludes=20 most of the SE). Hypobiosis occurs when environmental conditions = are too=20 cold (winter) or too dry (summer).=20 Trichostrongylus=20 colubriformis (Bankrupt worm) Trichostrongylus colubriformis is a very = small=20 threadlike worm and is the most predominant small intestinal worm. = It is=20 found in goats throughout the US, but seems to thrive better under = more=20 cool and wet conditions similar to T. circumcincta. = However, in=20 the southeast US, this worm is the next most common and important = after=20 Haemonchus and on some farms can cause considerable = problems. As=20 with Telodorsagia, this worm feeds on nutrients in mucous and = interferes=20 with digestive function resulting in diarrhea. It is called the = bankrupt=20 worm because death is seldom the end result and animals just = become poor=20 doers leading to loss of production and income. Nematodirus=20 spp. (Long-necked bankrupt worm) Nematodirus spp. are relatively large = worms (easily=20 seen) and can be found in goats throughout the US although usually = in=20 rather small numbers. Problems are rare in the southeast, but in = cooler=20 areas of the US there is a possibility of greater numbers of worms = accumulating. If heavy infection occurs, production and income = losses will=20 result (similar to that of T. colubriformis). Oesophagostomum spp. = (Nodular=20 worm) Oesophagostomum spp. are relatively large = (easily=20 seen) worms and can be found in goats throughout the US, usually = in rather=20 small numbers. These worms feed on blood and can contribute to the = overall=20 anemia being caused by H. contortus. Although this worm = resides=20 in the large intestine, the larvae are found in the mucosa of both = the=20 small and large intestine where they form nodules, thus the name = nodular=20 worm. Once the larvae leave these nodules they reside in the large = intestine. Trichuris spp. are usually found in small = numbers=20 and the posterior end of the worm is rather large and can be seen. = The=20 anterior end of the worm is thread-like, thus the name whipworm. = These=20 worms are also blood feeders and, like Oesophagostomum,=20 contribute to the overall blood loss due to other worms. Female = worms=20 produce characteristic =91football=92 shaped eggs with protruding = plugs at=20 each end. Diagnostic Methods (Measure = How Wormy=20 Animals Are)General appearance/signs Parasitized animals can show many signs of = infection=20 depending on the parasites present. The general signs include = rough hair=20 coat, diarrhea, depression, weight loss (or reduced weight gain), = bottle=20 jaw and anorexia (off feed). Laboratory diagnostic findings may = include=20 anemia (low PCV), increased FEC and loss of plasma protein.
The FEC (specifically for H. contortus) = has been=20 shown, for the most part, to reflect the animals' worm burden and = also=20 serves as an indicator of seasonal changes in level of infection. = Trends=20 in FEC over time can be seen, thus reflecting the relative = direction of=20 infection. When worms other than H. contortus = predominate, FEC is=20 a less accurate predictor of adult worm burdens. It is important to know that if heavy infection = occurs over=20 a short period of time (1-2 weeks) with Haemonchus, = animals may=20 lose substantial amounts of blood with few eggs in the feces as = the=20 prepatent period is about 3 weeks. Nematode parasites can affect an animals=92 = ability to=20 maintain erythropoesis (making red blood cells). The PCV is the = percent of=20 the blood that is red blood cells and normal is usually above 30%. = When=20 PCV drops below 20%, symptoms of anemia usually start to appear. = PCV is=20 determined by centrifuging blood in a capillary tube (similar in = size to a=20 ball point pen refill) which packs the cells and percent is = measured. All=20 nematode parasites can result in chronic anemia where red blood = cells are=20 not being made fast enough to keep up with demand. Of special = note, H.=20 contortus can lead to substantial acute blood loss and death. = PCV=20 values have been used to support other response criteria, and is = not=20 necessarily used as a "stand-by-itself" diagnostic tool. Level of anemia can be roughly evaluated by = observing the=20 color of mucous membranes which are areas where there are a lot of = capillaries (very small blood vessels) close to the surface so = that tissue=20 color reflects blood color. Such areas are inside the lower = eyelid, the=20 gums (only where pigmentation is not present) and inside the = vulva. If=20 such membranes are pale (essentially white), impending death is = near and=20 deworming is indicated immediately.
FAMACHA=A9 has been extensively tested in South = Africa and now=20 the US with excellent results. It has been shown that where = animals have=20 been examined at weekly intervals and salvage treatments only were = administered, up to 70% of adult animals may not require deworming = and=20 only a few required more than one treatment. Compared to previous=20 treatment regimens, total number of treatments may be decreased by = up to=20 90%. Since most of the worms would not be exposed to dewormers, = this=20 reduces the development of dewormer resistance. Information on = FAMACHA=A9=20 and training workshops (held in many localities) can be found on = the=20 website of the Southern Consortium for Small Ruminant Parasite = Control=20 (SCSRPC, http://www.scsrpc.org/). Worm count and = identification The most absolute and direct method for = documenting the=20 number of worms present in an animal is to open it up and collect, = identify, and count the worms present. When an animal dies, this = can only=20 be done by a properly trained veterinarian or other professional = and it=20 might be very expensive. However, one can get an idea of the = magnitude of=20 Haemonchus infection by looking for the worms that are = visible on=20 the lining of the abomasum. It should be noted that for this to be = of any=20 value, the animal can not have been dead for very long. The = fresher the=20 animal is after death, the greater the chance to find worms = because after=20 death, the worms will move as far down the gut as they can get and = eventually die. It is important to note that Telodorsagia = and=20 Trichostrongylus are too small to see except under a = microscope.=20 Even if thousands of these worms are present, they cannot be seen = by the=20 naked eye while mixed in with the gut contents. Dewormers = (Anthelmintics)Dewomers are chemicals (drugs) that have been =
evaluated and=20
tested (effectiveness and safety) for use in animals to remove =
worm=20
parasites. For the most part, pharmaceutical companies will not =
market a=20
dewormer unless it is essentially 100% effective. As long as =
dewormers=20
remain effective (at the manufacture=92s recommended dosage), =
control is=20
relatively easy and cost effective. However, resistance to almost =
all=20
dewormers has been developed by many worm species. Therefore, =
reliance on=20
the use of dewormers has become limited. Only FDA approved =
dewormers (see=20
The three general classes of dewormers are = benzimidazoles,=20 imidazothiazoles and macrolides. The more commonly used = benzimidazole=20 dewormers are fenbendazole (Safeguard, Panacur) and albendazole=20 (Valbazen); imidazothiazole dewormers are levamisole (Levisol, = Tramisol)=20 and morantel tartrate (Rumatel) and macrolide dewormers are = ivermectin=20 (Ivomec) and moxidectin (Cydectin). Of these, only fenbendazole = and=20 morantel tartrate are approved for use in goats. All others would = be used=20 as extra-label. A number of these dewormers have gone off patent = and are=20 now marketed under different generic names. Formulations of dewormers include drench, = injection and=20 pour-on. In addition, some dewormers are marketed in feed = supplement=20 blocks, mineral mixes, pellets and cubes. For goats, only the = drench=20 formulation of fenbendazole and the feed formulation of morantel = tartrate=20 are approved for use. Oral administration is preferred and with = drenches, it is=20 very important to make sure the product is delivered over the base = of the=20 tongue. By doing so, the dose is delivered to the rumen where it = will be=20 mixed with the ingesta and then distributed evenly throughout the=20 gastrointestinal tract. If the dose is delivered into the front = part of=20 the mouth, some may be spit out (wasted =3D reduced dose) and when = swallowed=20 the reflex may stimulate closure of the esophageal groove which = allows=20 what is swallowed to bypass the rumen. When the rumen is bypassed, = the=20 dose goes directly into the omasum (third stomach) and moves = quickly=20 through the gastrointestinal tract, thus not allowing sufficient = time for=20 the anthelmintic to achieve full effectiveness. The other form of oral administration is in feed = products=20 which does not ensure that all animals will receive an effective = dose=20 because individual animals utilize these products differently. = Some=20 animals eat more/less than others due to their appetite, their = place in=20 the "pecking order" or they just may not like the formulation=20 (specifically supplement blocks and mineral mixes). If one elects to use injectable products (not = recommended),=20 injections are subcutaneous (under the skin) and best administered = in an=20 area of exposed skin (usually under the front legs) so that one = can see=20 the dose being delivered. It is best to not "tent" the skin, just = lay the=20 needle on the skin and insert quickly. If the skin is tented, the = needle=20 may come out the other side and the injected material will be = administered=20 on the skin surface (again wasted). If the injection is given in = an area=20 covered by hair, it can be difficult to ensure that the needle = actually=20 penetrates the skin and the dose is delivered appropriately. = Sometimes the=20 injected material will run back out of the needle hole (again = wasted), so=20 make sure to press a finger over the injection site for a few = seconds to=20 prevent leakage. If one elects to use a pour-on product (not = recommended),=20 the material has to be delivered on to the skin. Parting of the = hair (if=20 long) may be necessary to achieve this. There are mixed reports as = to=20 whether pour-ons (approved for use in cattle only) work on goats. = For the=20 most part, pour-ons do not seem to be that effective in goats. = Table 1. Commonly used dewomers in goats = (Oral route=20 of administration only)
Make sure that the exhibition center provides = adequate=20 housing, that pens are cleaned and disinfected and that = ventilation is=20 adequate. Make sure that all animals entering the show will be = examined by=20 the show veterinarian and that all state and local animal health = laws will=20 be enforced. Work with your veterinarian to establish a herd = health=20 program for your show goats and for the goats staying home that = will be=20 exposed to the show goat on its return. Do not mask signs of = illness in=20 your goat. If it is sick then stay home. Make sure that you have a = Scrapie=20 Tag for your goat (wethers excluded) and that you have any = required health=20 tests performed and that you have a current Certificate of = Veterinary=20 Inspection. Minimize stress on your goat by providing it with a = pen that=20 is as close to those in the exhibition facility as is possible and = use the=20 same bedding, feed and water source as you will have at the show. = Keep=20 fans on the goat at home, the white noise they produce will be the = same as=20 you will recreate at the show. Transport your goat in your own = trailer.=20 Avoid traveling in a commercial trailer or commingling with other=20 livestock. The major problem encountered in controlling = nematode=20 parasitism in goats is the resistance that many worm populations=20 (specifically H. contortus) have developed to essentially = all of=20 our dewormers. Resistance has developed primarily because = dewormers have=20 been used and rotated too frequently and many times under-dosing = occurs.=20 Continuing to use such a dewormer will increase the selection of = more=20 resistant worms which will eventually result in a population of=20 "superworms" that can=92t be controlled with drugs. There is no = "silver"=20 bullet that can be relied on. Resistance is genetically controlled = and=20 once it is established, it is set in the population and those = dewormers=20 can no longer be used effectively. Control ProgramsSmart use of dewormers The most important aspect of using dewormers is to = conserve=20 their effectiveness. This can be achieved by using them as little = as=20 possible and only when infection levels dictate that intervention = is=20 necessary. The old concepts of treat all animals when a few show = signs or=20 all animals at regular intervals (shorter than every 3-4 months) = is no=20 longer warranted because it promotes dewormer resistance. Even if = new=20 dewormers are discovered and marketed (which is a long way down = the line),=20 they should not be used indiscriminately as that is the reason the = dewormer resistance problem has evolved. It would be prudent to establish which dewormers = are=20 effective against a worm population. This can be achieved by = conducting=20 FEC reduction testing and should be done by a qualified = professional such=20 as a veterinarian, veterinary school parasitology lab or a = diagnostic lab=20 that offers such a service. However, FEC are not hard to do, but a = microscope is required. The procedures for conducting a FEC are = available=20 on the SCSRPC and other websites. The concept is to do FEC before = and=20 after (10-14 days) treatment. If the counts after treatment are = "0"=20 (essentially 100% reduction), the dewormer is very effective. = However,=20 this should not be expected with most of the dewormers and the = best one=20 (highest % reduction) should be considered for use only when there = are no=20 other options, thus extending its useful life. Fecal egg count = reduction=20 testing may seem somewhat expensive, but it will be worth the = effort and=20 expense to know what you have. The worst thing is not knowing and=20 continuing down the wrong path. Once the most effective dewomer = has been=20 selected, using it along with others needs to be done "smartly." = Some of=20 these "smart" concepts are:
Mixed/alternate livestock species grazing For the most part, each livestock species harbors = it=92s own=20 parasite fauna except that sheep and goats have the same = parasites. Only=20 one worm species is known to be found in essentially all livestock = species=20 and that is Trichostrongylus axei, a minor abomasal worm = and one=20 not to be concerned about. If practical, cattle and goats can be = grazed=20 together where each consumes the parasites of the other which, in = turn,=20 reduces available infective larvae for the preferred host species. = If=20 co-grazing is not preferred, cattle and goats can be grazing = alternately=20 on the same pastures. Again, each consumes the others parasites = and when=20 returned to the same pasture, available infective larvae have been = reduced. Both livestock species should gain from this over time. = The one=20 situation that requires some care with this strategy is if there = are young=20 calves present. Calves can become infected with H. = contortus, but=20 problems in the calves should still be much less than that in the=20 goats. The concept of pasture rotation or rotational = grazing to=20 break the parasite cycle has been tossed around for years. The = main reason=20 to use pasture rotation is not for parasite control but to provide = the=20 most nutritious forage for growth and development. If grazed = correctly,=20 most forages reach the next most nutritious stage in about 30 = days, so=20 many rotation schemes have the animals returning to pastures at = around 30=20 day intervals. Unfortunately, this 30 day interval is also about = the same=20 time necessary to ensure that the previous worm parasite = contamination has=20 now been converted into the highest level of infectivity for the = next=20 grazing group. Thus, 30 day rotation schemes may actually lead to=20 increased worm parasite problems. In fact, heavy exposure over a = short=20 period of time can lead to disastrous clinical disease and losses. = Rotation schemes of 2-3 months have been shown to have some effect = on=20 reducing pasture infectivity in tropical and subtropical = environments=20 (maybe SE US), but in more temperate environments, infectivity can = extend=20 out to 8-12 months depending on the conditions. For the most part, = it is=20 impractical to leave pastures ungrazed for such extended periods = of time;=20 therefore, one needs to be aware of the possible problems = associated with=20 whatever rotation scheme being used. Some success at reducing = infectivity=20 can be achieved by cutting pasture for hay between grazing = periods. It=20 should also be emphasized that when rotation schemes are used, = stocking=20 rate is usually high and the resultant increase in contamination = may make=20 the problem worse. Copper oxide wire particles (COWP) have been = marketed for=20 years as a supplement for livestock being managed in copper = deficient=20 areas. COWP come in adult cattle, calf and ewe boluses (25, 12.5 = and 4=20 grams, respectively). Only the cattle boluses are available in the = US. Due=20 to potential toxicity in sheep, only one dose per year is = recommended. It=20 is also well known that copper has some anthelmintic activity = against=20 abomasal worms, but not other gastrointestinal worms. That makes = it a very=20 narrow spectrum product. But, in view of the potentially = devastating=20 problem of anthelmintic resistance by H. contortus, = recent work=20 has revisited the possibility of using COWP to specifically target = H.=20 contortus. Such work has shown that as little as a gram or = less and 2=20 grams may remove substantial numbers of H. contortus in = lambs and=20 ewes, respectively. Similar work in goats has not been tested = adequately=20 to establish what is needed, but similar doses may be appropriate. = As=20 mentioned, copper has to be used cautiously in sheep because = toxicity can=20 develop due to liver accumulation. Toxicity may not be an issue in = goats=20 as they have been reported as not being that sensitive to excess = copper=20 intake. Thus, higher doses and/or more treatments during = haemonchosis=20 season may be useful in goats. Condensed tannin containing = forages An approach to parasite control that has not been = adequately=20 explored in the US is use of medicinal plants with anthelmintic=20 properties. There is growing evidence in work from New Zealand and = Europe=20 that grazing or feeding of plants containing condensed tannins = (CT) can=20 reduce FEC, larval development in feces, and adult worm numbers in = the=20 abomasum and small intestine. There are a number of CT-containing = forages=20 that grow well throughout the southern US, but most of these have = not been=20 tested for their potential anthelmintic properties. Preliminary tests with sericea lespedeza (SL, = Lespedeza=20 cuneata), a CT-containing perennial warm-season legume, have = shown=20 positive effects of reduced FEC in grazing goats, and in sheep and = goats=20 in confinement when the forage was fed as hay. In addition, an = effect on=20 reducing worm burden has also been reported. Similar results have = been=20 observed using CT-containing quebracho extract for small = intestinal worms,=20 but not abomasal worms. In addition to its potential use in controlling = worms, SL is=20 a useful crop for limited resource producers in the southern USA = It is=20 adapted to hot, drought climatic conditions and acid, infertile = soils not=20 suitable for crop production or growth of high-input forages, such = as=20 alfalfa. It can be overseeded on existing pasture or grown in pure = stands=20 for grazing or hay. Farmers could increase profits by marketing LS = anthelmintic hay, or using it themselves and reducing their = deworming=20 costs. In South Africa, SL has been reported to increase profits = with=20 rangeland farmers by bringing poor, drought-prone, infertile land = into=20 useful production for sheep, and any anthelmintic uses would = increase the=20 value of SL even further. The same is true in the southern US, = which has a=20 climate and soils ideal for growth of this plant. In addition to hay, SL is being evaluated in the = form of=20 meal, pellets and cubes to be fed as a supplement to grazing = animals or as=20 a deworming method under temporary short-term confinement. SL processed products are expected to become = available in=20 the near future. There is considerable evidence that part of the = variation in=20 host resistance to worm infection is under genetic control in = goats and=20 sheep. Resistance is most likely based on inheritance of genes = which play=20 a primary role in expression of host immunity. Based on survival = of the=20 fittest management conditions, several goat and sheep breeds are = known to=20 be relatively resistant to infection. Such breeds include: goat - = Small=20 East African, West African Dwarf and Thai Native; sheep - Scottish = Blackface, Red Maasai, Romanov, St. Croix, Barbados Blackbelly and = the=20 Gulf Coast Native. Katahdin sheep have been considered as being = more=20 parasite resistant, but studies to document this are few and not=20 conclusive. Using resistant breeds exclusively or in crossbreeding = programs would certainly lead to improved resistance to worm = infection,=20 but some level of production might be sacrificed. While such a = strategy=20 may be acceptable to some, selection for resistant animals within = a breed=20 is also a viable option. Selection for resistant lines within = breed has=20 been demonstrated with goats (Scottish Cashmere) and sheep (Merino = and=20 Romney). Within breed, animals become more resistant to infection = with age=20 as their immune system becomes more competent to combat infection. = However, some animals within such a population do not respond very = well=20 and remain relatively susceptible to disease. This means that the = majority=20 of the worm population resides in a minority of the animal = population. It=20 would make sense to encourage culling practices (based on FEC, = PCV,=20 FAMACHA=A9, etc.) where these minority "parasitized" animals were=20 eliminated, thus retaining more resistant stock. To augment this = process,=20 finding sires that throw relatively resistant offspring, would = speed up=20 this process. This approach has been used successfully in goats = (Scotland)=20 and sheep (New Zealand and Australia), but it may take quite a = long time=20 (up to 8-10 years) to achieve satisfactory results. Heritabilities = for=20 FEC, a common measurement for assessing parasite burden, range = from 0.17=20 to 0.40 which is quite good. Thus, selection for resistance and/or = selection against susceptibility using a measurement such as FEC = has been=20 moderately successful. The real benefit to this approach is that = reliance=20 on dewormer intervention for control can be reduced, thus = conserving the=20 activity of such dewormers for when they are needed.
To date, the only delivery system is incorporating = the=20 fungal spores into supplement feedstuffs that have to be fed = daily. This=20 requires a management system that can accommodate daily feeding to = ensure=20 that all animals consume an equivalent amount of feed. To achieve = adequate=20 control of larvae in the feces during the transmission season, = spores have=20 to be fed for a period of no shorter than 60 days. This can be = expensive=20 and time consuming. A bolus prototype is being developed which = would allow=20 a single administration where spores would then be slowly released = over a=20 60 day period. This product is not available at this time. As a consequence of drug resistance among worms of = grazing=20 ruminants, efforts have increased in recent years to develop = functional=20 vaccines. This has been made possible by newer technologies in = gene=20 discovery and antigen identification, characterization and = production.=20 Successful vaccines have been developed for lungworms in cattle = and=20 tapeworms in sheep. The most promising vaccine for nematodes has = been what=20 is called a "hidden gut" antigen and it specifically targets = H.=20 contortus. This antigen is derived from the gut of the worm = and when=20 administered to the animal, antibodies are made. When the worm = ingests=20 blood during feeding, it also ingests these antibodies. The = antibodies=20 then attack the target gut cells of the worm and disrupt the = worm=92s=20 ability to process the nutrients necessary to maintain proper = growth and=20 maintenance. Thus, worms die. This vaccine has been tested = successfully in=20 sheep under experimental conditions and has had limited success = under=20 field conditions. Reasons for this are unclear. Effect of this = vaccine on=20 H. contortus in goats has not been evaluated. The one = drawback to=20 this vaccine is that the antigen is normally "hidden" from the = host and a=20 number of vaccinations may be required to maintain antibody levels = high=20 enough to combat infection. This may be quite expensive. In = addition,=20 massive numbers of whole worms are necessary to extract limited = amounts of=20 antigen; therefore, this will only be practical when methods are = derived=20 to artificially make the antigen so that it can be mass produced = at a=20 lower cost. Vaccines for other worms that do not feed on blood = have=20 focused on using antigens found in worm secretory and excretory = products.=20 These antigens do have contact with the host and should stimulate=20 continuous antibody production. However, protection has been quite = variable and marketing such products has not been pursued. Vaccines are not available at this time. The control of worms traditionally relies on = grazing=20 management and/or dewormer treatment. However, grazing management = schemes=20 are often impractical due to the expense and the hardiness of = infective=20 larvae on pasture. Currently in the US, there are only 3 dewomers = approved=20 for use in sheep and 2 in goats. The 3 for sheep are levamisole = (Levasol=20 and Tramisol, oral drench), albendazole (Valbazen, oral drench) = and=20 ivermectin (Ivomec for Sheep, oral drench). The 2 for goats are=20 fenbendazole (Safeguard/Panacur, oral drench) and morantel = tartrate=20 (Rumatel, feed additive). Use of any other dewormers or other = methods of=20 administration are not approved and constitute extra-label use. = There are=20 FDA rules and regulations governing use of such drugs where = extra-label=20 use may be necessary. The evolution of dewormer resistance in worm = populations is recognized globally and threatens the success of = drug=20 treatment programs In South America, South Africa, and the = southeastern=20 US, prevalence of resistance to dewormers has reached alarming = proportions=20 and threatens future viability of small ruminant production. In = the only=20 comprehensive study in the US on prevalence of dewormer resistance = in=20 goats, 90% of all farms had resistance to 2 of 3 drug classes and = 30% of=20 farms had worms resistant to all 3 drug classes. Fortunately, the = one=20 dewormer that may still remain effective in some circumstances is=20 moxidectin (Cydectin). However, there are now several reports of=20 moxidectin resistance. There is an urgent and increasing need to = develop=20 alternative strategies that could constitute major components in a = sustainable worm control program.. The most promising of these = methods=20 that are immediately applicable are smart drenching, copper-oxide = wire=20 particles and FAMACHA=A9. An integrated approach using these current methods = should=20 have an immediate impact on productivity and profitability of = small=20 ruminant production systems in the southeastern US and other = regions where=20 H. contortus and/or other worms can be a problem. = Producers will=20 be able to reduce overall dewormer usage by integrating an = alternative=20 compound (copper-oxide wire particles) with identification of = animals in=20 need of treatment (FAMACHA=A9) and adopting smart drenching = procedures,=20 thereby reducing cost of production while improving animal health = and=20 productivity. Lower frequency of deworming will also reduce = potential=20 environmental impact of excreted anthelmintics and will decrease = the=20 development of resistance, thereby prolonging the usefulness of = available=20 dewormers. This integrated approach will provide a cornerstone for = inclusion of future environmentally sound worm prevention and = control=20 technologies to secure a sustainable, growing small ruminant = industry. Integration of other methodology/technology = certainly will=20 be instituted when evaluation is complete and ready for use.
Fasciola hepatica (Liver=20 fluke)
Diagnosis is by using a sedimentation procedure to = find eggs=20 in feces. Regular floatation techniques are not good as the = floatation=20 medium induces premature hatching of the eggs and they do not = float.=20 Clorsulon (Curatrem) is the only product that is effective against = immature flukes. Clorsulon and albendazole are effective against = adult=20 flukes. Therefore, selection of either of these depends on the = time of=20 year. Another liver fluke, the deer fluke (Fascioloides = magna),=20 can kill small ruminants by destroying the liver. Infection is = rare, but=20 should be considered where deer have access to pastures grazed by = small=20 ruminants. Control is difficult. Parelaphostrongylus tenuis = (Meningeal=20 worm) The meningeal worm (Parelaphostrongylus = tenuis),=20 also known as the deer worm or meningeal deer worm, frequently = infects=20 llamas, alpacas and sometimes goats. White-tailed deer are the = natural=20 host for the parasite, so goats are at potential risk everywhere = that=20 white-tailed deer are found. Small ground dwelling slugs and = snails are=20 intermediate hosts. Goats, which are not normal hosts, can ingest = the=20 slugs/snails harboring the infective form and the larvae migrate = into=20 places where they don't normally reside in the deer. Migration is = up the=20 spinal nerves to the spinal cord but then they seem to get lost. = The=20 larvae then migrate throughout the spinal cord and the brain = (actually=20 around the spinal cord and brain, not in it). This causes damage = to the=20 central nervous system which may be severe enough to result in = death. Animals can become infected in the spring, summer = or fall.=20 Disease is usually seen in the fall and winter about 3 to 4 months = after=20 infection. Often only one animal is infected at a time on a single = farm.=20 Infected animals will show a wide variety of symptoms which = include, but=20 are not limited to: rear leg weakness and ataxia (uncoordinated = walking),=20 paralysis, hypermetria (exaggerated stepping motions), circling, = abnormal=20 head position, blindness and gradual weight loss. Generally, = animals with=20 more severe symptoms have a worse prognosis. Diagnosis is difficult in the live animal and is = usually=20 made when animals die and the larvae are found on examining the = spinal=20 cord and brain microscopically. The use of ivermectin at monthly = intervals=20 during the transmission season (spring and summer) has been used = in=20 attempts to prevent infection, but this strategy has not been = proven.=20 However, this frequent administration interval most likely will = have an=20 effect on the development of resistance by the other resident = worms.
External Parasites = (Arthropods)General life cycles Life cycles of arthropods involve a series of = structural=20 changes known as metamorphoses, the actual sequence of which = varies with=20 different parasite groups. Complete metamorphosis begins when = adults lay=20 eggs from which larvae hatch (Figure 15A). The larval forms grow = and shed=20 their skins (moult) several times, each time to accommodate their=20 increases in size. Larvae either may live freely or may be = dependent on=20 their hosts for obtaining nourishment. Eventually a hard-cased = structure=20 called a pupa is formed, which may have the capacity to survive = winter.=20 The pupa hatches into the adult parasite, the final stage of=20 metamorphosis. Thus, there are four distinct stages in the life = cycle:=20 egg, larva, pupa, and adult. Incomplete metamorphosis involves a = larva=20 that grows and moults one or more times to become an adult-like = form known=20 as a nymph, which in turn grows and moults one or more times to = become an=20 adult (Figure 15B). In this case there are only three distinct = stages,=20 namely eggs, larvae, and immature adults (nymphs) that grow to = maturity=20 without further change in body type.
There are a number of fly species which are = primarily a=20 nuisance, especially under confinement conditions. The fly season = is=20 April-October. The constant buzzing of nuisance flies is = irritating and=20 can result in reduced foraging that may lead to production losses. = Blood=20 loss due to large numbers of feeding mosquitos, as can be = encountered in=20 the southeast, may lead to anemia, unthriftiness, and weight = loss/reduced=20 gains. However, these fly problems are not all that common and = control=20 measures are usually not emphasized. There are many insecticides = that can=20 be used for control when necessary. Routine disposal of manure and = organic=20 materials will help control nuisance flies, and the local mosquito = control=20 program will help control mosquitos. These parasites are relatively permanent residents = on the=20 animal. Infestation (commonly called mange when mites are = involved) may be=20 seen as intense irritation with the animal scratching and chewing = creating=20 skin lesions that can become ugly. They thrive and reproduce = during the=20 cooler months (October-March) of the year. Transmission from = animal to=20 animal is by contact, so crowding should be avoided. Control can = be=20 accomplished by using appropriate insecticidal products at the = onset of=20 cooler conditions and as necessary thereafter. Ticks thrive on blood obtained from the host. They = are=20 subdivided into hard and soft ticks according to structural=20 characteristics. The bodies of hard ticks are roughly oval and = pointed at the=20 front. The anterior segment is a false head the structure of which = may=20 help to identify them. The structures on the head anchor the tick = to the=20 host's skin and facilitate blood feeding. The abdomen, flattened = top and=20 bottom, can expand to several times its original size as a tick = feeds on=20 its host. This phenomenon, referred to as engorgement, is seen = only in=20 females. The patterns of pigmentation on the top side of the tick = also=20 helps with identification. A further classification of hard ticks = is made=20 based on whether their life cycle involves one, two, or three = hosts. Ticks=20 have a life cycle incorporating incomplete metamorphosis. Adult = ticks feed=20 and mate on mammals. Engorged females drop to the ground and lay = eggs. The=20 eggs hatch, producing larvae, called seed ticks. The seed tick = moults=20 twice, passing through a nymphal stage before reaching maturity. A = blood=20 meal must be taken before each moult can occur. Ticks are = classified as=20 one-, two-, or three-host ticks, depending on how many times they = drop=20 off, moult, and seek a new animal. A one-host tick remains on the = animal=20 from the seed-tick stage to maturity. A two-host tick drops off = the=20 initial host to moult from larva to nymph. The nymph seeks a = second animal=20 for the final blood meal before final moult to adult. The = three-host tick=20 drops to the ground for each moult, after which a new host is = sought. Soft ticks differ from hard ticks in many = respects. They=20 have a leathery outer skin rather than a hard cuticle, and both = males and=20 females engorge when feeding on the host. Their shapes vary among = species=20 and their false head is located on the bottom side of the tick = near its=20 front so it is not pointed as in hard ticks. Otobius = megnini, the=20 spinose ear tick, is an example of a soft tick. Only larvae and = nymphs of=20 this species are parasitic and can cause swelling of the ear = resulting in=20 scratching and signs of disorientation. Adults live in hidden = areas in the=20 environment, such as within cracks in the wood of barns. Insecticides recommended for other ectoparasites = will=20 control ticks. Dipping or high pressure sprays provide the best = results.=20 The spinose tick can be controlled by applying an insecticide = directly=20 into the ears. In general, most external parasites can be = collected with=20 various equipment. For flying insects, nets and aspirators are = used. For=20 crawling insects/ticks, jars, traps, combs and forceps are used. = For=20 mites, skin scrapings are used. Most external parasites can be = seen=20 readily and identified using published descriptions and keys. = However, the=20 use of a microscope is usually necessary. Sources of InformationBooks
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