Genetic parameters of functional and fertility determined length of productive life in Swedish dairy cattle

The objective oft his study was to estimate generic parameters and breeding values of sires for different definitions of length of productive life in Swedish Red and White dairy cattle. The data consisted of 534 016 daughters with initial calvings between 1988 and 1996. These cows were daughters of 1266 sires (55 of which were considered proven bulls, and treated as fixed effects). The model for the hazard included: a random time-dependent effect of herd-year-season (hys), a fixed time-dependent effect of year-season, a fixed rime-dependent effect of parity by stage of lactation, a fixed time- dependent effect of the cow's peak yield as deviation from her herdmates in hat herd-year, a fixed time-independent effect of age at first calving, an d random and fixed effects of sire. The hys effect was assumed to follow a gamma distribution and the random sire effect a normal distribution with me an zero and variance A sigma(s)(2), where sigma(s)(2), is the variance amon g sires and A the relationship matrix. Length of productive life teas defin ed as the number of days from first calving to culling or end of data. Two types of length of productive life were studied: (1) functional productive life (PL), all cows that were culled before the end of data were considered as uncensored; (2) fertility determined productive life (FPL), only cows t hat were culled for fertility problems were considered as uncensored. Herit ability estimates were 6.9% and 6.1% for PL and FPL, respectively. The appr oximated genetic correlation estimates between fertility measures in first lactation and FPL was higher than the corresponding estimates with FL. Tn c onclusion, if was feasible to use the trait fertility-determined length of productive life, its heritability was almost as large as for FL, and the ge neric correlation with fertility was higher than for FL. However, the expec ted selection response in fertility from indirect selection on FPL was lowe r than from direct selection.