Valutazione genetica del carattere longevità diretta mediante survival analysis e verifica dell'applicabilità nel piano di selezione della razza bruna attraverso la creazione di un indice combinato

Objective of this study is to improve the estimation of survival breeding values for Italian Brown Swiss Dairy Cattle. The genetic evaluation was carried out using survival analysis (Survival Kit). The trait “longevity” was never investigated with Survival Anlysis in Italian Brown Swiss Dairy Cattle. The Survival Analysis is the powerful methodology for investigate survival data. The trait investigated were the length of productive life (LPL) defined as the period between the first calving and culling. Data on 323’849 Brown Swiss daughters of 11’076 Brown Swiss Bulls were analyzed under a frailty proportional hazard model assuming a Weibull distribution for the baseline hazard function and including sire and herd-year as random effects. Estimated hazard ratios (HR) indicated that age at first calving, herd, parity, deviation (%) from the EVM herd-year mean and the interaction between herd size and the linear regression of herd yearly size based on 4 years were significant on LPL. The estimated variance for herd-year effect were 0,21 and for sire effect were 0,04. The effective heritability estimated was 12% and the equivalent heritability was 10% with 25% of censoring. The genetic (co)variance components and predicted breeding values among LPL and other traits analyzed by Italian Brown Swiss Cattle Breeders Association of about 1500 Bulls with already know Iterbull information were obtained using an Expectation-Maximization REML procedure based on the MACE equations. Eight different MT analysis were improved. Mean correlation between direct and combined breeding values was 97% ranging from 94,5% to 99,2% Mean of reliability improvement obtained was 0,05 ranging from 0,03 to 0,06.