Management and control of nematode parasites of small ruminants in the face of total anthelmintic failure.
Total failure of modern broad spectrum anthelmintics to control nematode parasites of sheep and goats is a reality, of rapidly increasing dimension, on many farms in the tropical / subtropical regions of the world. This is primarily associated with the highly pathogenic, blood sucking parasite, Haemonchus contortus, and where it now cannot be controlled by chemotherapy, annual mortalities exceeding 20% of the flock can be expected. Thus sheep and goat enterprises become totally unsustainable, unless major changes in management are effected. These must include a change away from reliance on suppressive anthelmintic treatment and to include several non-chemotherapeutic management options. In situations where livestock numbers need to be preserved and there is no opportunity to increase the grazing area available, then zero grazing with cut-and-carry herbage from uncontaminated pasturelands is the only option. In other circumstances stocking rates need to be substantially reduced, so that short-term rotational grazing can be effectively practiced. This strategy is improved if it is combined with the biological control of the free-living stages of the parasites, using the microfungus Duddingtonia flagrans. Monitoring the parasitological status of the animals by faecal sampling sentinel sub-flocks for nematode faecal egg counts, or the use of the FAMACHA procedure, are also valuable tools. Improving overall nutrition of the flock is an important adjunct to control. As a long-term priority, attempts to change the genotype of the flocks to those breeds that have been shown to possess natural resistance to H. contortus are worthwhile.
Waller
P J
PJ
Department of Parasitology (SWEPAR), National Veterinary Institute, SE- 751 89 Uppsala, Sweden.