Infections with parasites are common in small ruminants, but their impact on health largely depends on management. The barberpole worm, Haemonchus contortus, is the most important intestinal worm in the majority of small ruminant operations in the United States but is found worldwide with in increasing distribution. Other economically important nematodes include Teladorsagia circumcincta, Cooperia curticei, Trichostrongylus spp. In addition, coccidiosis can be a major problem in young animals and especially recently weaned lambs and kids in close housing conditions.
Adult Haemonchus contortus attach to the mucosa of abomasum and small intestine and consume blood. In contrast, Trichostrongylus spp. and other nematode parasites live in the small intestine and do not consume blood. Hence, severe blood loss and anemia are clinical features of only H. contortus infections. Other clinical signs of parasitism include unthriftyness, rough hair coat, bottle jaw, and death. The development of nematodes from eggs to adult worms depends on environmental moisture and temperatures, and takes only a few days in warm, moist climates. In the southeastern United States, parasite infections are a problem throughout the year. During periods of drought or cold weather, H. contortus undergoes hypobiosis, and large numbers of eggs are shed when weather conditions become more suitable for parasite development. Similarly, coccidia must sporulate outside of the host, and sporulation is influenced by environmental conditions. Moderate temperatures and moisture enhance sporulation, and both unsporulated and sporulated oocyst can survive for extended periods of time in the environment.
Some differences exist in the environmental risk factors for intestinal parasite infestation. Recently weaned lambs and kids are at greatest risk for coccidiosis when congregated on small pastures that result in excessive accumulation of oocysts. Clinical coccidiosis is rare when animals have ample excess to pasture and browse. Additional risk factors include stress of transport, weaning and feed changes. Overstocking is among the largest risk factors for parasitism. When close housing is unavoidable, routine removal of feces and feeding of animals above the ground from elevated troughs and hay-racks is essential. Goats and sheep on permanent pastures without access to browse are at risk for parasite infestations. As nematode larvae climb onto blades of grass up to a height of 2-4 inches, over-grazing is detrimental. This is especially true for goats that prefer a diet containing 80% browse (i.e. shrubs and bushes) and 20% grass, and, in general, have less immunity against intestinal nematodes. Goats should have abundant access to woody browse and will prefer young growth of bushes and trees over pasture grasses. It is reported that 30-35% of animals in a given herd harbor the majority of parasites. Identification and removal of high shedders from herds and implementation of rotational grazing programs will reduce the nematode burden of all herd members.
Management of parasitism in small ruminants cannot solely rely on the use of dewormers. While dewormers, used appropriately, can still be a tool in the management of parasites, in most herds, Haemonchus contortus has developed resistance against one or all of the three currently available classes of dewormers. The frequent occurrence of resistance to dewormers must shift the focus of parasite control away from deworming to alternative management options, which include:
1) Improvement of housing and pasture
(a) Provision of browse and high quality feeds
(b) Implementation of rotational grazing
(c) Feeding in elevated feed bunks and hay racks
2) Assessment of parasite burden in herd by:
(a) Routine fecal flotation
(b) Egg-count quantification by McMaster’s technique
(c) Assessment of anemia with FAMACHA program
3) Identification of anthelmintic resistance
(a) McMaster on fecal samples before and 7-10 days after deworming
Deworming must result in >90 % reduction in egg count
(b) DrenchRite assay
Cultures parasites in vitro, similar to bacterial sensitivity testing
4) Removal of highly infested shedders and genetic selection of small ruminants inherently resistant to parasites
5) Appropriate deworming of only those animals that need it
6) Biosecurity to keep animals with resistant parasites off the farm
7) Alternative control methods:
a) Copper oxide particles
b) Grazing of different livestock classes (e.g. graze sheep after horses)
c) High tannin-containing forages: e.g. Sericea lespedeza
d) Nematode trapping fungi
To discuss parasite control that is appropriate for your herd please contact your local veterinarian or Auburn University College of Veterinary Medicine at 334-844-4490.
For information on parasite control strategies in small ruminants, please visit: http://www.sheepandgoat.com/ACSRPC/