Genetic parameters of longevity traits of an upgrading population of dairy cattle.

Longevity reflects the ability of a cow to avoid being culled for low production, low fertility, or illness. Longevity could be used in breeding programs if genetic parameters were known. Various measures are used for longevity. In this study, lifetime measures including number of lactations, total milk production, number of days in lactation, herd life, and length of productive life were analyzed. Also analyzed were stayability measures (dead or alive) to 36, 48, 60, or 72 mo of age and to 12, 24, 36, or 48 mo of productive life. Measures of longevity were also analyzed after correction for milk production during first lactation (functional longevity traits). Data on 1,72,988 cows were used to calculate means for longevity traits per year of birth. All cows were known to have been culled. Longevity decreased from 1978 through 1984 and increased in 1985. Possible causes for the decrease of longevity were implementation of the quota system and introduction of Holstein genes. heritabilities of longevity traits were estimated for cows born in 1985 (38,957 records), 1982 (166,324 records), and 1978 (94,935 records) after data were edited to require at least 25 daughters per sire and 10 cows per herd. Phenotypic and genetic correlations were estimated for the 1985 data. Heritability estimates differed between years of birth, and estimates of functional traits were lower than those of uncorrected longevity traits. Genetic correlations between uncorrected longevity traits were high (0.733 to 1.000); phenotypic correlations were lower (0.131 to 0.980). Genetic correlations between uncorrected and functional longevity traits were high (0.577 to 0.975).