Ultimate Disease Resistance in Sheep: What Are the Relationships between All Major Diseases?

A study is described which is unique in that resistance to each of the major diseases which affect production in Merino sheep was measured in the same flock under the same environmental conditions. Results indicated that within the one flock, genetic variation exists for resistance to internal parasites, foot-rot, fleece rot and dermatophilosis. Heritability estimates were similar to those published from separate resource flocks. Results also showed that genes conferring resistance to one disease do not, in general, have any effect on resistance to other diseases. The exceptions to this general rule are that resistance to internal parasites and dermatophilosis have some genes in common (a positive association), as do resistance to fleece rot and footrot (a negative association). Practical implications for industry to develop Merino strains with ‘broad based’ disease resistance are discussed.