Veterinary Viewpoints: Controlling Internal Parasites In Sheep And Goats

About the author: Lionel J. Dawson, BVSc, MS, DACT, is a professor, specialist in swine and small ruminants at Oklahoma State University College of Veterinary Medicine, and extension vet at Langston University.

Treatment of gastrointestinal parasites, particularly the barber pole worm or Haemonchus contortus, is a primary concern for all sheep and goats. Gastrointestinal parasites cause significant economic losses and are listed among the three most common fatal diseases in sheep and goats. The development of deworming resistance to almost all three classes of anthelmintics available makes control difficult and encourages alternative management strategies.

Veterinarians can work with producers to develop integrated approaches to parasite control by looking at the specifics of the host, parasite and environmental interactions. The barber pole worm thrives in warm and humid conditions and has the ability to go through hypobiosis. In other words, it is metabolically inactive in the host in adverse weather conditions and occurs when conditions improve.

Infectious larvae survive for one to two months in hot summer months and more than four months in cooler, wet months. During the joke and lamb season, there is an increase in the periparturial egg shedding in the feces, which contaminates the environment. A good knowledge of the life cycles of parasites is required to create control programs.

There are three classes of anthelmintics available in the United States:

However, only morantel, thiabendazole, fenbendazole, albendazole and phenothiazine are permitted for goats. Thiabendazole and phenothiazine are not available. Other de-wormer products that are labeled for cattle and sheep can be used on goats with an additional label.

Deworming resistance occurs when the fecal egg count is reduced by less than 95% 14 days after administration. Resistance has increased due to frequent use of anthelmintics, excessive rotation, underdosing, or using a dose designated for cattle. Sheep and goats metabolize the worming agent faster than cattle, so their dosage is higher than cattle.

If the mucous membrane of an animal is greater than 3 in the FAMACHA score, it must be dewormed.
Control strategies must rely on the intelligent use of worming agents. This means that you only treat the animals that need to be dewormed and keep a pool of susceptible worms called refugia in your animals. Refugia mates with resistant worms to prolong anthelmintic use. Smart deworming strategies for blood-sucking worms like Haemonchus use the FAMACHA system to assess the color of the eye mucous membranes and assess anemia or blood loss. Another useful strategy for other worms is a five-point check (bottle jaw, coat, diarrhea, body condition, and nasal secretions for nasal bots).

Periparticular deworming is a mainstay of many internal parasite control programs. The deworming of all peripheral animals in early spring leaves only minimal refuge on the pasture and can accelerate the resistance. Do not deworm 15 to 25% of animals that do not show clinical symptoms to provide enough sanctuary. An Australian study recommends deworming periparurient pups or yearlings who are carrying more than two fetuses and older ones as they tend to lose more eggs.

Because of the increased resistance to deworming in goats compared to sheep, the simultaneous combination of two or three classes of wormers at their respective dosages has been used with some success. Selective deworming with a combination of different classes in the appropriate doses at the same time is beneficial to promote refuge, but can also promote resistance to all available wormers. Instead of deworming your entire herd, check the mucous membrane around the eye and dewormer the animals with a FAMACHA value greater than 3.

It is very important to use alternative control methods along with selective deworming with copper oxide wire particles, which have been shown to be significantly effective (70% to 90% FECR) against Haemonchus. The doses are low. Be careful with sheep as they are very sensitive to the accumulation of copper in the liver and are prone to copper poisoning. There is a very narrow safety margin for the copper requirement for maintenance in sheep at 10 ppm to toxic levels at 25 ppm. Check with your veterinarian before using copper oxide boluses on sheep and goats.

Small ruminant owners need to be aware that good nutrition is important to reduce the severity of internal parasitism. The literature reports on the positive effect of supplemental proteins and in particular of non-degradable bypass or rumen protein on increasing the resistance to internal parasites. Protein aids in tissue repair and provides essential amino acids to stimulate an immune response.

Veterinary Viewpoints is offered by the faculty of the OSU Veterinary Medical Teaching Hospital. The American Animal Hospital Association-certified hospital is open to the public and provides routine and specialized care for all animal species, as well as 24-hour emergency care, 365 days a year. Call 405-744-7000 for an appointment or more information.