Genetic evaluation for mortality and calving ease in Holstein dairy herds
Genetic selection for improved health and longevity is a major goal of dairy cattle breeders however; little attention has been paid to the genetic component of calf mortality. Calving ease is a risk factor for mortality up to a month after birth in dairy calves. So, the aim of this study was to estimate of heritabilities and correlation between mortality and calving ease at first parity. After preparation of data by means of the software package SAS (9.1), records of 53436 Holstein calves born in the years 1991 to 2011 from 59 herds were analyzed. A linear bivariate sire-model was fitted to the data and average information, REML was used to estimate (co)variance components. The frequency of mortality and calving ease were 2.6, and 4.22%, respectively. heritabilities for mortality and calving ease were 0.0022 , and 0.039, respectively. Genetic correlation between two traits was -0.11, and significant from zero. Non-genetic correlation was low (0.038), but significant from zero. This study has shown that genetic variation for two traits exists and suggests that different genes affect two traits.