Lambs grazing Periparturient egg rise Close grazers Sheep feces Barber pole worm Image source: Hair sheep Workshop Parasitized lamb Anemia Bottle jaw Tapeworm segments Coccidiosis Deer transmit meningeal worm Coccidiostat in mineral Safe pasture Rotational grazing Mixed species grazing Gulf Coast Native sheep Image source: scsrpc.org St. Croix ewes Image source: scsrpc.org Katahdin Fecal sampling McMaster slide Strongyle eggs Image source: Hair sheep Workshop FAMACHA© card FAMACHA© Cydectin® Administer all anthelmintics orally Syringes for deworming Copper oxide wire partices Sericea lespedeza Chicory Supplemental feeding Zero grazing controls parasites In most sheep production areas, internal parasites or gastro-intestinal nematodes ( worms) are usually the primary disease affecting sheep and lambs. Sheep are more susceptible to internal parasites than most other types of farm livestock for several reasons. Their small fecal pellets disintegrate very easily thus releasing the worm larvae onto pastures. They graze close to the soil surface and to their feces. They acquire immunity more slowly. It takes 10 to 12 months for many lambs to develop immunity to parasites. Sheep also suffer a temporary loss of immunity around the time of lambing, called the periparturient egg rise. Heavy stocking rates and insufficient pasture rest periods contribute to the incidence of parasitic disease in sheep and lambs. Internal parasites tend to be much less of a problem under range-type conditions where sheep do not graze the same pasture twice in the same grazing season. They are also less of a problem in dry climates (or during dry periods) because parasites require moisture for their development. In the past, sheep producers relied heavily on anti-parasitic drugs called "anthelmintics" (dewormers) to control internal parasites in their flocks. But the long-time use and in some cases misuse of these drugs has resulted in parasites that have become increasingly resistant to anthelmintics. Drug resistance has been documented in all three drug families and is most commonly reported with the benzimidazoles and avermectins. Some farms are experiencing complete anthelmintic failure. In the U.S., few anthelmintics are FDA-approved for use in sheep and lambs, and no new drugs are likely to be approved. No combination products are available. As a result, producers must develop more integrated programs for controlling parasites, which do not rely exclusively on drug therapy. They must also learn to use the existing drugs more judiciously. The Parasites Gastro-Intestinal Worms (roundworms, nematodes, stomach worms) In warm, moist climates, the parasite that causes the most problems is usually Haemonchus Contortus, better known as the "barber pole" or wire worm. The barber pole worm is a blood-sucking parasite that pierces the lining of the abomasum (the sheep's fourth or "true" stomach), causing blood plasma and protein loss to the sheep. Females are identified as barber pole worms because their white ovaries are wound around their red blood-filled intestine. Male worms are red. The barber pole worm is the largest and most deadly stomach worm. The worms are visible during necropsy. The symptom most commonly associated with barber pole worm infection is anemia, characterized by pale mucous membranes, especially in the lower eye lid; and "bottle jaw," an accumulation (or swelling) of fluid under the jaw. Infections with barber pole worm rarely result in diarrhea (scours). Other worm species are more likely to cause diarrhea. The barber pole worm can be difficult to control because it has a short, direct life cycle and is a prolific egg layer. A female barber pole worm can produce 5,000 to 10,000 eggs per day. The barber pole worm is also capable of going into a "hypobiotic" or arrested state when environmental conditions are not conducive to its development and resuming its life cycle once environmental conditions improve. Some worm larvae are able to survive on pastures over the winter, depending upon climate. Worms usually of secondary importance include Trichostrongylus spp. and Teladorsagia (Ostertagia). Their importance is usually as an additive effect in mixed infections with Haemonchus. However, in warmer sub-tropical areas, Trichostrongylus spp. are important pathogens in grazing ruminants. Teladorsagia appears to be much less important in the United States than in cooler parts of the world such as Northern Europe and the British Isles. In the southern United States, Ostertagia circumcincta is of no real significance in small ruminants because the hot and often dry summers are hostile to the survival of its pre-parasitic stages In the western U.S. particularly the cooler, wetter, coastal areas of Washington, Oregon and Northern California, Teladorsagia is the dominant nematode of sheep (and goats). Nematodirus is not usually a significant problem in small ruminants in North America. However, Nematodirus battus does cause significant disease in lambs in Britain because of its unusual hatching requirements. Cooperia infections are usually secondary contributors to parasitic disease. Tapeworms (Moniezia spp.) Because tapeworm segments can be seen in sheep feces, they often cause alarm to producers. While experts disagree about the importance of effects of tapeworms, there is little evidence to suggest that treatment is beneficial to the host. Although dramatically large numbers of tapeworms may occupy the small intestine, damage to sheep is generally much less than that done by the gastrointestinal Haemonchus. In extreme cases, tapeworms may cause intestinal blockages. They may affect gut motiblity, which could predispose lambs to enterotoxemia. There is some evidence that lamb growth rates may be affected when large numbers of tapeworms are present. Tapeworms have an indirect life cycle. They require pasture mites to complete their life cycle. Only certain anthelmintics (benzimidazoles, praziquantel) are effective against tapeworms. Lungworms (Dictyocaulus filaria, Muellerius capillaris) Wet, low-lying pastures and cool, damp weather favor the development of lungworm disease in sheep. Lungworm eggs are passed in the feces. After the eggs hatch and are ingested by the sheep, they travel through the sheep's tissues to the lungs (trachea and bronchi). Only in severe infestations do lungworms produce clinical disease, causing fever, coughing, nasal discharge, rapid breathing, and poor performance. Secondary infection by bacteria may cause death. Liver Flukes (Fasciola hepatica) Liver flukes can cause death in sheep and lambs or liver damage in sub-acute cases. In the U.S., they are primarily a concern in California, the Gulf States and Pacific Northwest. Liver flukes require snails as an intermediate host. Two drugs are available in the United States for the treatment of liver flukes: Clorsulon and Albendazole. Meningeal Worm (Paralaphostrongylus tenius) The meningeal (deer or brain) worm is an internal parasite of white tailed deer. The life cycle of the meningeal worm requires terrestrial snails or slugs as intermediate hosts. Sheep are unnatural, dead-end hosts for the parasite. When sheep ingest snails containing infective larvae, the parasite moves into the brain and/or spinal cord causing often fatal neurological disease. The neurological signs observed in infected sheep depend upon the number of larvae present in the nervous tissue and the portion of the brain or spinal cord that has been affected. A mild infection may produce a slight limp or weakness in one or more legs, while a more severe infection may cause an animal to be partially or completely paralyzed. Meningeal worm infection cannot easily be diagnosed in the live animal. Treatment usually involves high, repetitive doses of anthelmintics, along with steroids and other supportive therapies. Research by Cornell University has demonstrated good efficacy with high doses of fenbendazole, along with anti-inflammatory drugs. Preventative measures include fencing off areas which receive high deer utilization and removing sheep from pastures before weather turns cool and wet. Fencing sheep away from likely snail and slug habitats (e.g. ponds, swamps, wetlands, low lying and poorly drained fields, and woodlands) may also help to prevent the problem. In high risk areas, monthly deworming (with ivermectin) has been advocated. Coccidia (Eimeria spp.) is discussed in another chapter. Integrated Parasite Management (IPM) Good Management Internal parasite control starts with good management and common sense. Sheep should not be fed on the ground (unless the ground is frozen). Feeders which cannot easily be contaminated with feces should be favored for grain, hay, and minerals. Water should be kept clean and free from fecal matter. Pastures and pens should not be overstocked. When new sheep are acquired, they should be isolated from the rest of the flock for at least 30 days and aggressively dewormed to prevent the introduction of drug-resistant worms. Use of Clean or Safe Pastures Clean or safe pastures are pastures which are not contaminated with worm larvae that affect sheep. Examples of clean pastures include pastures that have not been grazed by sheep (or goats) for the past 6 to 12 months; pastures which have been grazed by horses or cattle; pasture fields in which a hay or silage crop has been removed; pasture fields which have been rotated with field crops; and pastures that have been recently established or renovated by tillage. Pasture Rest and Rotation It is a common misconception that rotational grazing controls internal parasites in sheep. Intensive rotational grazing may actually contribute to parasitic problems. This is because rotating large groups of ewes and lambs through small paddocks concentrates livestock and infective parasite larvae onto the same small area. Researchers in the Netherlands found that it takes three months of rest for an infected pasture to return to a low level of infectivity. Researchers at Langston University (Oklahoma) determined that a 65-day rest period was sufficient (for goats). Rotational grazing is an effective management tool for managing parasites, but only if pasture rest periods are long enough (i.e. 60 days or more). On the other hand, better nutrition provided by rotational grazing may offset the effects of higher parasite loads on the pasture. Grazing Strategies Approximately 80 percent of the worm larvae can be found in the first two inches of grass. Therefore, sheep grazing taller forages should have fewer parasite problems. Sheep should not be allowed to graze forages shorter than 3 inches in height. Sheep that browse also have fewer parasite problems. Another grazing strategy is to wait until the dew has lifted from the grass or grass has dried after a rain. Dry conditions force parasites to stay at the base of the plants where they are less likely to be consumed by the livestock. Multi-species Grazing Sheep (and goats) are generally not affected by the same internal parasites as cattle and horses. Consequently, pastures grazed by cattle and horses are safe(r) for sheep (and goats) and vice versa. Sheep can be co-grazed with cattle and/or horses. A leader-follower system can be utilized or pastures can be alternated between sheep and cattle and/or horses. There are numerous other benefits to multi-species grazing. Each species has different grazing behavior that complements one another. For example, sheep prefer to eat weeds and short, tender grasses and clover, while cattle prefer to eat taller grasses. Cattle may offer some protection from predators. Alternative Forages Some pasture plants have deworming properties, such as those containing condensed tannins. Research has shown that sheep grazing tannin-rich forages have lower fecal egg counts than animals grazing traditional grass pastures. The tannins may also decrease the hatch rate of worm eggs and larval development in feces. Forage species which contain high levels of condensed tannins include sericea lespedeza, birdsfoot trefoil, and chicory. Sericea lespedeza is a warm, season legume. Birdsfoot trefoil is a long-lived perennial legume. Chicory is a low-growing, leafy perennial. Generally speaking, trees and shrubs contain higher levels of tannins than pasture grasses, and tropical legumes contain more condensed tannins than temperate legumes. Nematode-trapping fungus BioWorma® is the tradename for a product which contains spores of a fungus called Duddingtonia flagrans. When fed to grazing animals, the fungus spores trap and kill worm larvae in the manure, thereby preventing contamination of pastures. The fungus does not have any effect in the animal. Parasitized animals still require deworming. It works on the free-living stage of roundworms. It needs to be fed daily to have any effect. BioWorma® is being marketed by an Australian company. It was approved for sale in the US in 2018 and became available for purchase in 2019. There are two products. BioWorma® contains 34% fungal spores and can be purchased by veterinarians and feed mills. Livamo® with BioWorma® contains 2.4% fungal spores and is available for purchase by producers. Premier 1 Supplies, of Iowa, was the first US distributor of Livamol® with BioWorma®. It began selling BioWorma® by itself in 2020. Healthy Soil Earthworms have been shown to ingest worm eggs and larvae, either killing them or carrying them below the soil surface. Certain types of fungi will trap and kill parasitic larvae. Dung beetles ingest and disperse manure, thus keeping eggs and larvae from developing. Anything that is done to maintain soil health and promote these types of organisms will aid in parasite control. Scientists are examining the possibility of feeding nematophagous fungi to livestock to kill larvae in manure piles. Nutritional Management Supplemental feeding can aid in the control of parasites. Sheep and lambs on a higher plane of nutrition mount a better immune response to internal parasites than animals whose nutritional status is compromised. Animals on low protein diets are more susceptible to infection because they produce less IgA (immunoglobulin). Higher levels of protein have been shown to improve the pregnant ewe's immune response to parasites after lambing. Lambs receiving protein supplementation usually have reduced fecal egg counts. Zero Grazing Keeping sheep and/or lambs in confinement or dry lot (i.e. "zero grazing") is a proven means of reducing parasitism and preventing reinfection. Under a zero grazing situation, sheep and/or lambs do not have access to vegetation for grazing. They are housed in a bedded barn, dirt lot, or facility with slatted floors. Feed should be fed off the ground in feeders. Watering containers should be kept free from fecal matter. Slatted floors offer the best protection against internal parasites because sheep generally do not come into contact with their feces. Genetics Genetics is probably the best long term strategy for controlling internal parasites in sheep. Some sheep breeds are naturally more resistant and resilient to internal parasites. They include the "native" breeds of the Southeast (Florida, Louisiana, and Gulf Coast Native and the Florida Cracker) and hair sheep breeds with tropical origins: St. Croix, Barbados Blackbelly (and its derivatives), and hair sheep composites, such as the Katahdin. Grazing resistant breeds of sheep with susceptible breeds, may act to “sweep” pastures and reduce contamination to susceptible animals. Regardless of the breed raised, producers can breed sheep which are more resistant to parasites by culling ewes that are persistently affected by parasites and favoring parasite resistant ewes and rams in their selection programs. Both fecal egg counts and FAMACHA© scores can be used to identify sheep with resistant and susceptible genetics. In New Zealand, it is possible to select rams that shed 60 to 70 percent fewer parasite eggs than historical averages. In the US, the National Sheep Improvement program (via Australia's LambPlan) provides EBVs for parasite resistance (fecal egg counts) in Katahdin sheep. Other breeds are now beginning to submit fecal egg count data. EBVs can be calculated for other breeds once fecal egg count data is submitted to NSIP. Scientists are currently looking for genetic markers for worm resistance so that a DNA test could be used to show producers which of their animals are resistant to internal parasites. Proper Anthelmintic Use Anthelmintics are still an important part of parasite control. However, they must be used judiciously ensure effectiveness of treatment and slow down the rate by which worms develop drug resistance. To start with, the weights of sheep and lambs must be known or accurately approximated in order to calculate the proper dosage of medicine. Underdosing results in the survival of worms which are resistant to the anthelmintic used. Underdosing is one of the major causes of increasing anthelmintic resistance. Flocks should be divided into groups for deworming or drenching equipment should be calibrated for the heaviest animals in the group. Oral drenching is the recommended method of treatment for sheep. Oral medications should be delivered over the tongue. If the medicine is deposited into the mouth to stimulate the closure of the esophageal groove and bypass the rumen. If an anthelmintic is more slowly absorbed in the gut, drug levels are prolonged and the treatment may be more effective. Thus, fasting sheep for up to 24 hours may improve efficacy of dewormers, especially when using benzimidazoles and ivermectin. However, water should not be restricted. To prevent the introduction of drug-resistant worms, you should deworm newly purchased animals with drugs from at least two of the three anthelmintic families. Moxidectin should be favored over ivermectin due to its superior potency. Levamisole should probably be the other choice, since widespread resistance is believed to exist in the benzimidazole group of dewormers. After deworming, the animal(s) should be released onto a wormy pasture to help dilute any "super-resistant" worms that may remain in his system. Combination treatments It is now recommended that clinically-parasitized animals (as evidenced by FAMACHA© score, Five Point Check© or other criteria) be given combination treatments. A combination treatment is when you give different drugs to kills the same worms. Treatment is maximized because of the additive effect of the different dewormers. The recommendation is to give the most potent drug from each drug class, usually albendazole (Valbazen®) + moxidectin (Cydectin®) + levamisol (Prohibit® or LevaMed®). Ideally, each drug is dosed using a separate syringe. The drugs should not be mixed because they are not chemically compatible. The drugs are administered sequentially at the labeled dose. The withdrawal period is the withdrawal period of the drug with the longest withdrawal. Anthelmintics (dewormers) available in the U.S. Drug class Ingredient Trade names BZD Benzimidazole Fenbendazole Albendazale Oxtendazole Panacur®, SafeGuard® Valbazen® Synanthic® IMID Nicotinic agonist Imidazothiaoles Tetrahydropyrimidines Levamisole Morantel Pyrantel Prohibit®, Levasol®, Tramisol®, LevaMed® Rumatel®, Nematel®, Strongid® ML Macrocylic lactone Avermectins Milbemycins Ivermectin Epinomectrin Doramectin Moxidectin Ivomec®, Primectin® Eprinex® Dectomax® Cydectin®, Quest® Only Valbazen® drench, Ivomec® drench, Prohibit® and LevaMed® drench, and Cydectin® drench are FDA-approved for use in sheep in the United States. Anthelmintic resistance It is recommended that producers test for anthelmintic resitance every 2 to 3 years. There are two ways to test for anthelmintic resistance. The primary method is the fecal egg count reduction test (FECRT). Before and after fecal egg counts are compared. An effective treatment should reduce fecal egg counts by 95 per… truncated (9,132 more characters in archive)
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