SHEEP 104
TRACY LOCKE ZULICK, DVM
INTERNAL SHEEP PARASITES
Sheep are the most widely distributed kind of domestic animal, found in nearly all countries of the world. Internal parasites cause considerable losses in sheep flocks through reduced weight gains, lower wool production, poor reproductive efficiency, and even death. Sheep are particularly susceptible to worm infestations because of their tendency to crop vegetation close to the ground. The following is a discussion of some major parasites of sheep and recommended methods of control.
CESTODES
The tapeworm Moniezia is commonly found in ruminants. Mature proglottids (egg sacs) in the feces are easily spotted with the naked eye and look like pieces of slimy noodles. I usually begin to see these 3-4 weeks after putting the lambs on to pasture. Although generally regarded as of little pathogenic significance, heavy infestations can cause unthriftiness, diarrhea, and even intestinal obstruction. Lambs infected with Moniezia are more susceptible to Enterotoxemia (see Sheep 103). Albendazole, fenbenazole or praziquantal are currently FDA approved products effective against this group of parasites.
H.O.T.C. COMPLEX
Haemonchus, Ostertagia, Trichostrongylus and Cooperia
The nematodes of the abomasum (true stomach) and small intestine cause the greatest loss of production in grazing sheep. Larvae are ingested with the damp morning grass and may develop into adults shedding eggs in as little as 2-3 weeks. In the warm months while sheep are on pasture, this short life cycle allows for rapid contamination of the pasture, re-infection of the sheep, and a rapidly multiplying load of infectious larvae by the end of the summer.
Haemonchus and Ostertagia have the ability to go dormant and burrow in the wall of the abomasum for the winter. This dormant phase can cause a lot of ulceration and scarring to the stomach wall. The parasites will emerge when stimulated by the hormones of late pregnancy and delivery and by the temperature rise in the spring, and are thereby reintroduced to the pastures and the new spring lambs.
Nematode infection can cause poor growth, decreased feed efficiency and milk production, weight loss, diarrhea, anemia, edema (bottle jaw) and death. Haemonchus is the most significant parasite with respect to clinical disease and anthelmintic (dewormer) resistance.
COCCIDIA
Several types of the protozoa Eimeria can regularly be found in sheep. While typically not a problem in adults (most are carriers) in young lambs coccidiosis causes diarrhea, anorexia, dehydration, weakness, and death. .Clinical disease is common after the stress of weaning, feed changes, or shipping. Creep feeding lambs can help minimize fecal contamination from adults. Lambs should not be overcrowded and kept in a clean and dry environment. The best treatment is prevention. Grain treated with a coccidiostat like lasalocid or decoquinate in late pregnancy can reduce the number of oocysts shed by the dams. Additionally, medicated feed in the lamb creep for at least 4 weeks can control the disease and allow the lambs to develop a natural immunity. Medicated feed should not be fed year round to avoid drug resistance in the coccidia.
Internal parasite treatment and control has recently become complicated. The parasites are resistant to many dewormers and we cannot depend on stronger or newer drugs to solve the problem. Traditional methods of parasite control – like treating the whole flock before putting on to new pasture, etc (see Sheep 102!) are being challenged. New theories advocate treating only anemic or sickly sheep (Famancha method) thereby limiting the pasture contamination with potentially resistant worms. Other options include using natural or organic products like garlic to treat parasites (www.garlicbarrier.com). Please consult your veterinarian for the most appropriate parasite management method for your farm and follow through with fecal analysis testing.