Internal Parasite Control in Sheep and Goats

Part I: Signs and Symptoms of Internal Parasites in Sheep and Goats

Barber pole worms are the most common internal parasites of concern for U.S. sheep and goats as they are highly pathogenic, adaptable, voracious feeds, prolific egg layers, and have a short life cycle. Relatively warm and wet climates of the U.S. make barber pole worms problematic for producers across the nation, and even more so for those in the southern and southeastern regions. However, other worm species can also pose challenges for small ruminants, including the black sour worm, brown stomach worm, hookworm, tapeworm, lungworm, liver fluke, and meningeal (or deer) worm, to name a few. Coccidia is different from other internal parasites as it is a single-celled protozoa. Nonetheless, coccidiosis can seriously threaten the health and productivity of young animals. While worms are transmitted in pasture settings, coccidia is transmitted through direct contact with feces and primarily affects animals younger than 6 months of age, especially those housed in confinement.

Understanding how to control these parasites begins with understanding their life cycle. Depending on the worm species, internal parasites will inhabit the stomach, small intestine, or large intestine of their host. They feed on blood, depriving precious nutrients from the host animal. As adult worms feed and reproduce, eggs are deposited in the host’s feces. With favorable climatic conditions (usually warm and wet), eggs will hatch into larvae and begin maturing. As larvae molt to an infective stage, they will utilize moisture droplets from rain or dew to migrate up forages making themselves more available to be consumed by grazing animals. Once consumed, larvae mature into adults and the cycle continues. Disrupting this cycle can be challenging since infective larvae can be active in temperatures ranging from 40 to 95 degrees Fahrenheit, and thus, can persist in pastures for weeks or even months waiting for a host. Barber pole worms have among the shortest life cycle of all parasitic nematodes and can mature from eggs to infective larvae in as quickly as 3 to 4 days in favorable conditions.

Common symptoms of internal parasite infection can include anemia, edema, scours, lethargy, weakness, poor performance, loss of body weight, and poor hair coat. Animals are more likely to become infected if they are experiencing nutritional and/or physiological stress, such as malnourished animals, lambs or kids with minimal immunity, pregnant or lactating females, and breeding stock. Some individuals may show a natural resistance against parasitic infection. For example, sheep breeds of Caribbean origin, like the hair breeds, tend to be more resistant to infection. Additionally, goats are generally more susceptible than sheep, especially the Boer, Angora, and dairy breeds.

Identifying clinical symptoms of parasitic infection can be done few ways. The FAMACHA© eye anemia system is the most common for helping identify individuals suffering from barber pole worm infection. The primary symptom of barber pole worm infection is anemia, which can be detected most easily by examining the mucous membranes of the inner bottom eyelid. Level of anemia is then determined by comparing the color of the mucous membranes to the color chart on the FAMACHA© card, which can only be acquired by attending an approved FAMACHA© training course. Anemia is graded on a 1 to 5 scale, 5 being severe. It is recommended that individuals scoring 4 or 5 receive treatment. Those scoring 1 or 2 do not need treatment, and additional evaluations may be needed to determine if those scoring 3 need to be treated.

A helpful test for FAMACHA© score 3’s and for determining infection by parasites other than the barber pole worm is the 5-point check. As suggested by the name, the 5-point check draws attention to five areas of the body that are generally affected in a parasitic infection: 1) mucous membranes in the eyes are tested using the FAMACHA© system; 2) the jaw is examined for evidence of swelling as edema (or “bottle jaw”) is common with severe cases; 3) the back is examined for body condition score (BCS) as affected animals usually lose fat cover; 4) the tail is checked for evidence of scours; and 5) the nose is examined for discharge which may be evidence of nasal bots. In goats, it might also be important to check for coat condition as infected animals can develop rough hair coats.

These parasite screening tests should be repeated frequently during peak transmission season and can be followed up with fecal egg counts (FEC) if there is any lingering uncertainty. Manure samples can be sent to laboratories that conduct FEC tests or supplies can be acquired to do the tests on-farm. Average fecal egg count varies by species, breed, and individual, but it is generally recommended to treat young, pregnant, and breeding animals if FEC is greater than 1,000 eggs per gram (epg) and to treat mature, non-breeding animals if FEC is greater than 2,000 epg.

[This is the first of a two-part series on internal parasite control. More information to come in Part II: Treatment and Prevention of Internal Parasites in Sheep and Goats.]

Information used in this article was gathered from the American Consortium for Small Ruminant Parasite Control. For even more information on how to identify, treat, and control parasites, visit the American Consortium for Small Ruminant Parasite Control website.

Part II: Treatment and Prevention of Internal Parasites in Sheep and Goats

[This is the second of a two-part series on internal parasite control. Refer to Part I for more information on signs and symptoms of internal parasites in sheep and goats.]

Treatment of internal parasites has become increasingly important as years of inadequate and whole-flock treatment has created a parasite population that is growing resistance to all classes of dewormers available for use in the U.S. The current suggested treatment strategy is to adopt a targeted selective treatment approach (TST). Targeted selective treatment involves only treating individuals that require or would benefit from treatment as determined by clinical signs discussed in Part I of this series. Dewormers should be used as treatment only and not as prevention. Treating all individuals in a flock whether they are symptomatic or not will increase the likelihood of killing susceptible parasites and leaving behind only the resistant strains to continue breeding and laying eggs. As the proportion of resistant parasites grows, dewormer efficacy decreases and will ultimately become useless. Conversely, a TST approach will help ensure some susceptible parasite strains remain in the population and that dewormers will continue to remain effective. Moreover, by utilizing TST you can more easily record any individuals consistently requiring recurring treatments and cull them from the flock.

In addition to TST, it is recommended to treat affected individuals using a combination of dewormers from at least two different dewormer classes. Refer to the table below for products approved for sheep and goats that fall into each of the three classes of dewormers.

Delivering dewormers in combination does not mean mixing two or three together and administering in the same syringe. Rather, it means delivering a single dose of each dewormer in separate syringes at the same time. In goats, an example would be giving a full dose of SafeGuard® immediately followed up by a full dose of Prohibit®. There may be worms in the population that are resistant to only SafeGuard® or only Prohibit®, and hopefully only a small percentage are resistant to both. Therefore, a greater proportion of resistant worms can be targeted and killed with combination treatments, increasing the overall efficacy. An effective treatment will reduce fecal egg count (FEC) by 95%, and anything less indicates resistance.

General guidelines for utilizing dewormers is to always get an actual weight on animals before treating. Underestimating weight could lead to underdosing which can continue the development of resistant parasite strains. Because parasites inhabit the gut, it is recommended to deliver dewormers orally for maximum effectiveness, unless another method of administration is prescribed on the label. Always be sure to carefully follow instructions on the product label for target species, dose rate, route of administration, and treatment frequency. A veterinarian must be consulted for extra-label use of any treatment product.

Copper oxide wire particles (COWP) have been identified as a potential alternative treatment, specifically for barber pole worm infections, by delivering a slow release of copper oxide. There is evidence to show COWP can be especially beneficial when used in combination with dewormer treatments. Depending on the age of animals to be treated, one-half to two grams COWP are packed in boluses and delivered orally. Extreme caution should be used in delivering COWP to sheep as copper can be toxic. It is best to know the copper status of your flock before administering.

Coccidiostats, such as monensin in goats, lasalocid in sheep, and decoquinate in young, non-lactating lambs and goats, are approved for prevention of coccidiosis, but there are currently no FDA-approved drugs to treat coccidiosis in sheep and goats in the U.S. A vet must be consulted for extra-label use of amprolium or sulfonamides in sheep and goats to control coccidia. Based on preliminary studies, it has been suggested that the legume sericea lespedeza and oregano essential oil may be beneficial in controlling coccidiosis outbreaks.

Equally as important as the appropriate treatment of parasites, if not more so, is good husbandry, nutrition, and pasture management to help control parasites and reduce the need for treatment. Good hygiene and sanitation are especially critical for managing outbreaks of coccidiosis. Waterers, feeders, and barns should be cleaned regularly to minimize fecal contamination. Animals should not be overcrowded, and nutritional, physiological, and environmental stressors should be minimized as much as possible. For grazing animals, consider moving water or feeding stations around the pasture to minimize animals congregating in the same area for extended periods.

Providing adequate nutrition is essential for many reasons, one of which being proper immune function. A diet balanced in protein, energy, vitamins, and minerals will support growth, production, and the immune system in a way that helps animals resist and become more resilient to parasitic infection. For example, the immune system requires protein. Animals will prioritize protein for maintenance, growth, and production, then the immune system. If insufficient dietary protein is provided, the animal may not have enough remaining protein to mount an adequate immune response against infection. Additionally, dietary energy helps increase or maintain body condition score (BCS). Body condition score is a good indicator of nutritional status, and thin or nutritionally stressed animals are usually more prone to parasites. Finally, pregnant dams consuming a high-quality diet with adequate protein and energy will produce high-quality colostrum to support their young in fighting off parasites.

Appropriate pasture management can help minimize the risk of animals picking up parasites in pasture settings. Most parasite larvae are found in the bottom three inches of plant material and can survive without a host in a wide range of temperatures for as long as they have stored energy. Therefore, most management strategies revolve around decreasing overgrazing, resting pastures, and physical or mechanical clean-up of pastures. These include rotational grazing, utilizing browse, harvesting hay, planting annual forages, and grazing multispecies. Frequently relocating animals to different pastures, allowing animals to browse wooded areas, and harvesting hay off grazing pastures can all provide rest for pastures and allow time for larvae to die off. These strategies also help control overgrazing and increase grazing height above where larvae are usually found. Discing ground to plant annual forages and grazing cattle or horses in rotation with sheep offer mechanical and physical clean-up of pastures. Discing existing forages allows sunlight to reach the soil and kill larvae. Cattle and horses are not affected by the same internal parasites as small ruminants and can clean up pastures by consuming and removing larvae off the land.

The value of genetic selection in preventing parasitic infection should not be overlooked. Estimated breeding values (EBV) provide a way to determine an individual’s projected resistance to parasites based on their genetics. As mentioned in Part I of this series, baseline FEC is highly variable between individuals, but is also a moderately heritable trait. When available, individuals should be selected or culled based on their weaning (WFEC) or post-weaning (PFEC) fecal egg count EBV. Negative values for WFEC and PFEC are desirable. An animal with a PFEC value of -25 indicates they have an average FEC that is 25% below that of their breed average, and thus have greater parasite resistance than the average animal of their breed.

As an aside, a couple alternative methods that show promise for preventing parasitic infections are the use of forages rich in condensed tannins and a product called BioWorma®. Condensed tannins are plant metabolites that have been shown to inhibit larval development of barber pole worms. Therefore, incorporating forages rich in condensed tannins, such as sericea lespedeza, birdsfoot trefoil, chicory, sainfoin, pine bark, black locust trees, and tropical legumes, can help reduce FEC. BioWorma® is a feed-through fungus that traps and kills larvae in the manure. While feeding BioWorma® can help prevent the spread of parasites, actively affected animals will still require treatment.

Treatment and control of internal parasites in sheep and goats can be expensive and time consuming, but if not managed well, the health and financial impacts of parasites on growth and production can be just as costly. It is important to note that internal parasites affecting sheep and goats can also be transmitted to deer and camelids, such as llamas and alpacas which are often used as guard animals for small ruminants.

Information used in this article was gathered from the American Consortium for Small Ruminant Parasite Control. For even more information on how to identify, treat, and control parasites, visit the American Consortium for Small Ruminant Parasite Control website.