Genetics of disease resistance inBos tauruscattle

Abstract

SummaryThis review summarises evidence for genetic variation ofBos tauruscattle to diseases encountered under temperate conditions, including internal and external parasitism, susceptibility to mycotoxic diseases (tall fescue toxicosis, facial eczema, ryegrass staggers), mastitis, ketosis, pasture bloat, leukosis, tuberculosis, foot and mouth, brucellosis and BSE. Averaging mean heritability estimates reviewed from 8 diseases (weighted equally) gave a value of 0.21, indicating that measurable genetic variation for disease traits inBos tauruscattle is somewhat less than that for production traits, such as milk yield or body weight. Many estimates, however, have high standard errors, and there could be an upward bias resulting from non-reporting of zero or non-significant estimates.Few single-trait selection experiments have been conducted to study the genetics of disease resistance traits in cattle. For the disease traits where selection is being applied extensively, index selection for improved disease resistance and increased production is more common than single-trait selection. Results from a long-term (25 year) divergent selection experiment with resistance/susceptibility to pasture bloat in cattle in New Zealand are reviewed. Four single-year experiments comparing progeny of ‘high’ versus ‘low’ sires for resistance to disease are also reviewed, one in Australia studying faecal nematode egg counts, one in the USA involving the mycotoxic disease, tall fescue toxicosis, a third in New Zealand involving the mycotoxic disease, facial eczema, and a fourth in the USA involvingBrucella abortus.