When modern selection for milk yield procedures were introduced concern was expressed about the possible deterioratior. of stayability and lifetime performance. A series of papers both American and British (e.g. Parker et al., 1960, Van Vleck, 1964 and Robertson and Barker, 1966) indicated however that the high producers in the first lactation not only continued to outproduce their lower-producing first-lactation mates in later lactations but also had a substantially longer herd life. Rendel and Robertson (1950) illustrated that longevity as such has litvle economic value compared with high yield but stressed that freedom from disease and constitutional well-being are important characters. The fact that cosiderable differences exist between daughter groups in longevity has been illustrated many times. Andersson (1980) found that breeding values for per cent culled in the first lactation varied from 16.5 to 26.9 among Swedish Red and White bulls with high breeding values for yield. If all bulls were included, the highest figure was 39.1. Bakker, Everett and Van Vleck (1980) proposed a profitability index for sires, developed from sire evaluations for milk yield, fat yield and s-ayability. If disease costs and daughter fertility can be included in a profitability index of the type described by Bakker et al. (1980) the economic efficiency of the selection may be improved.

B. Lindhe

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 7. Symposia (1), , 336-343, 1982
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