Genetic analysis of functional, fertility-, mastitis-, and production-determined length of productive life in Swedish dairy cattle

Abstract

Our objective was to estimate genetic parameters for different definitions of longevity: (1) length of productive life (PL), all cows culled before the end of data collection were considered as uncensored; (2) fertility-determined PL (FPL); (3) mastitis-determined PL (MPL); and (4) production-determined PL (PPL): only cows that were culled due to fertility problems, mastitis-related problems, or production, respectively, were uncensored. Survival analysis was used and the hazard was modelled as: a random time-dependent (TD) effect of herd–year–season, fixed TD effects of parity by year–season, parity by stage of lactation, parity by the cow’s peak yield deviation from herd–year–mates (not for PPL), parity by age at first calving, and random effects of the cow’s sire and maternal grandsire. Apart from in first lactation, there was a high risk of culling during the first 10 days of lactation for PL and MPL. Thereafter the culling risk decreased abruptly, and then increased steadily by stage of lactation. For FPL, the culling risk was very low up to 180 days of lactation. The risk of being culled due to mastitis was increased between 180 and 270 days of lactation. The risk of being culled due to low production was low during the first lactation and in later lactations the highest risk was between 180 and 270 days of lactation. For PL, FPL, and MPL, there was a general increase in culling risk with increasing parity, and cows in the lowest peak yield classes ran a far higher risk of being culled. Heritability estimates were 6.3, 10.0, 17.9, and 24.9% for PL, FPL, MPL, and PPL, respectively. Approximate genetic correlations between fertility, mastitis, and milk production traits and FPL, MPL and PPL, respectively, were higher than corresponding correlations with PL. The expected selection response in fertility and mastitis from indirect selection for FPL and MPL was lower than from direct selection, but higher than if PL was used as selection index trait.