Ecological and host-genetic control of internal parasites of small ruminants in the Pacific Islands

• Ministry of Agriculture and Lands, Solomon Islands
• Ministry of Agriculture, Tonga
• Department of Agriculture and Fisheries, Samoa
• Department of Agriculture, Vanuatu
• University of the South Pacific, Samoa
• Ministry of Agriculture, Fisheries and Forests, Fiji

In an effort to increase meat production on land not suitable for cropping or cattle, Pacific Islanders have increasingly turned to husbandry of small ruminants. However, there are two major constraints: sub-optimal nutrition (which is being addressed by other aid agencies) and internal parasitism. At present, farmers must drench their stock every 34 weeks in order to contain heavy mortality and production losses. However, as well as being costly and difficult to distribute, anthelmintics have rapidly led to widespread parasite resistance, so much so, that if alternative solutions are not found, it is possible that commercial production of goats and sheep in the Islands will cease.
In a previous ACIAR project (8418), scientists from the CSIRO Division of Animal Health, who have considerable expertise in parasite control, assisted colleagues in Fiji to elucidate the epidemiology of small-ruminant internal parasites in that country and develop potential control methods. These include a minimal drenching program to reduce both the rate of development of anthelmintic resistance and the cost of control; a grazing-management system that requires little or no drenching; and the possibility of breeding lines of goats and sheep selected for their innate resistance to internal parasites. To aid the design of management strategies aimed at parasite control with minimum use of anthelmintics, a computer simulation model was constructed.
The present project is designed to capitalise on the earlier work by carrying it through to completion. CSIRO researchers will collaborate with colleagues in Vanuatu, Solomon Islands, Samoa and Tonga in continuing the epidemiological work to determine how control methods developed in Fiji can be deployed in those countries.
The epidemiology of internal parasites of small ruminants will be defined for the four countries and the tropical parasite computer simulation model will be validated against field data and adapted for use as an extension tool. Parasite population dynamics will be compared for goats and sheep and incorporated into the simulation model. Using the model, sustainable parasite control programs will then be developed, involving minimal drenching and grazing-management systems. Successful control strategies will be refined and tested at experimental sites and control systems will be set up on key farms for extension purposes. The economic impact of the control systems will also be assessed and extension officers will be trained in the use of control techniques. The CSIRO Division of Animal Health will provide laboratory support for the control program.
Heritability of host resistance will be determined for both goats and sheep by performance and progeny testing. If this is sufficiently high, selection programs will be established on the major goat and sheep-breeding stations of the Pacific Islands.
The research is expected to slow down the speed of onset of parasite resistance, reduce the cost of parasite control, permit farms where multiple drug resistance has developed to stay in business, and develop lines of goats and sheep that require little or no anthelmintic treatment. Goat and sheep farmers in the Pacific Islands will produce more meat. In turn, this will reduce imports and the related drain on foreign currency reserves. There are likely to be spillover benefits to other tropical regions, particularly parts of Southeast Asia.
The epidemiology and resultant control methods may also have application in parts of Australia similar in climate to the Pacific Islands. In addition, CSIRO parasitologists believe that anthelmintic resistance may develop more frequently in goats and then be transferred to sheep. Comparison of parasite generation times and turnover rates in conjunction with drenching practices in the two species may well influence decisions on the advisability of grazing goats with sheep in Australia.