Project Number: 1265-32000-084-02
Project Type: Specific Cooperative Agreement

Start Date: Sep 01, 2007
End Date: Aug 31, 2010

Objective:
1. Improved diagnosis of gastrointestinal nematodes by the use of a DNA-based, ¿multiplex¿ PCR technique that is simple, sensitive and rapid, and allows the user to simultaneously test for 5 different genera of GI nematodes infecting cattle or sheep and can be used on DNA isolated from parasite eggs. 2. Identification of genetic resistance markers that could be used to make informed breeding decisions in terms of minimizing the effects of the parasites on production.

Approach:
Historically, control of GI nematodes was accomplished by complicated management programs which kept stocking rates low and minimized the exposure of susceptible animals to heavily infected pastures. The development of broad spectrum, highly efficacious anthelmintic drugs changed the nature of parasite control programs, and has resulted in a situation where parasite control now relies almost exclusively upon the repeated administration of drugs to a large percentage of herd members. However, this increase in drug usage has resulted in the selection of resistant parasites world-wide, and coincides with heightened consumer anxiety over chemical residues in food and the environment. Consequently, there is a trend towards alternative livestock systems which are perceived as being more Asustainable@, and as such, limits the use of anthelmintics. For livestock producers, it is important that they identify animals harboring high numbers of parasites, determine which parasite species are present on their farms, and whether or not the parasites infecting their animals are resistant to drug intervention. Genetic methods developed by USDA researchers can play a role in addressing all the above listed problem areas. Recent studies have shown that resistance to GI nematodes is controlled by multiple loci within the ruminant genone. Current efforts are directed toward using modern methods in genomic analysis to identify the natural genetic variation underlying resistance and susceptibility to GI nematodes, and to characterization of molecular markers for this trait. Accurate knowledge of genes controlling resistance will offer producers alternatives for disease control. For non-organic producers, susceptible animals can be targeted for drug administration. This approach reduces both the cost of anthelmintics used and the likelihood of drug resistance. A second option would be to target susceptible animals for immunotherapy involving vaccines or immunomodulation once the precise immunological pathways are elucidated. A final option would be selection to remove susceptible animals from the herd. Producers at high risk for parasite-induced production losses, such as organic producers or those in geographic areas with high rates of transmission would benefit the most from this strategy. In contrast, producers in areas or using management systems where the impact of the parasites is less severe could chose to select against susceptibility within the broader breeding goals of their programs.