GENOMIC TOOLS TO IMPROVE PARASITE RESISTANCE

Authors: SONSTEGARD, TAD - USDA, ARS, ANRI, GEML; Gasbarre, Louis

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2001
Publication Date: 11/22/2001
Citation: SONSTEGARD, T.S., GASBARRE, L.C. GENOMIC TOOLS TO IMPROVE PARASITE RESISTANCE. VETERINARY PARASITOLOGY. vol. 101, pp. 387-403, 2001.

Interpretive Summary: Ruminants show large differences in their ability to resist infection by gastro-intestinal(GI) worms. These differences could be used to control infections in the herds without using drugs to kill the worms. However, traditional methods in breeding selection have not been effectively applied to this problem due to the difficulty and expense of accurately identifying gresistant animals in a commercial production setting. To begin to identify the genetic basis for these differences in resistance, economic trait loci (ETL) are being identified and mapped in a resource population of Angus cattle selected and characterized for worm resistance and susceptibility to the two most common worm parasites of US cattle. The characterized population is composed of 5 generations of half-sib progeny with complete records of the animal's resistance pattern seen after a controlled infection. Three distinct resistance patterns are seen; innately yimmune, acquired immune, and highly susceptible. The individual genome of each animal has been characterized using markers (N=199) that are spaced at regular intervals over the 29 chromosomes of the cattle. Although initial ETL detection may be limited by the number of animals available, the unique family structure of this population provides additional detection power. Once the frequency of occurrence and the magnitude of the effect of each chromosomal location are determined in this population, tests associated with ETL most beneficial for controlling parasite infection can be accurately used for selection. Comparable information from humans and other species of biomedical importance will be utilized in the future to identify and characterize the genes underlying these ETL.

Technical Abstract: The natural genetic variability of the ruminant immune system provides a feasible means to control gastro-intestinal (GI) parasite infection without anthelmintics. However, the paradigm of traditional selection has not been effectively applied to the moderately heritable traits of parasite resistance (h~0.3) due to the difficulty and expense of gathering accurate ephenotypes in a commercial production setting. These characteristics make host traits related to GI nematodle infection ideal candidates for genomics-based research. To initiate explanation of important allelic differences, economic trait loci (ETL) are being identified and mapped using a resource population of Angus cattle segregating for GI nematode resistance and susceptibility to the two most common nematode parasites of US cattle, Ostertagia ostertagi and Cooperia oncophora. The population is composed of 5 generations of half-sib progeny with complete phenotypic records produced from controlled infections. To detect the genomic locations of the three distinct phenotypic traits being expressed (innately immune, acquired immune, and immunologically non-responsive ), genotypes have been generated for DNA markers (N=199) spaced at regular intervals ( 20 cM intervals) throughout the entire genome (3,000 cM). Although initial ETL detection may be limited by half-sib family size, the unique structure of this population provides additional statistical power for refining map position of potential ETL. After allele frequency and contribution to phenotype are determined,marker tests associated with ETL most beneficial for controlling parasite infection can be used for selection. Comparative map and functional genomic information from humans and other species of biomedical importance will be utilized.