Heritability of lifetime milk yield and productive life and their relationship with production and functional traits in the Simmental, Swiss Fleckvieh and Red Holstein populations in Switzerland.

Costs of milk production can be reduced through lower replacement rate by increasing productive life of cows. Lifetime production (LP, production to 6 th lactation) and productive life (PL, number of completed lactations) of 112,850 daughters of 766 test AI bulls were used to obtain daughter averages and to estimate heritabilities. Bulls belonged to three sections of the Swiss Simmental and Red&White cattle herd book, differing in percentage of Red Holstein genes. Correlations of daughter average LP and PL with sire EBVs for production, functional and type traits and with composite indices differed among herd book sections and, in some instances, changed signs (e.g., for correlations with EBV for linearly scored muscling) due to different breeding objectives. The strongest correlations of LP were found with EBV milk (>0.69), of PL with total merit index (0.44 to 0.52) and the composite fitness index (0.32 to 0.56). Heritabilities were estimated using two sire models (without or with including a fixed effect of herd book section). They were around 0.19 and 0.13 for LP, and 0.111 and 0.097 for PL from the two models. Estimates obtained from the first model may be more appropriate because breeding objectives differ among herd book sections.