Study of some important factors affecting mortality in female calves and heifers in different periods from Birth to first calving

The aim of this study was to estimate mortality rates in dairy calves and heifers up to 760 day of age and identify risk factors for calf mortality. The records of 52,311 female calves born in the years 1998 to 2009 from 50 Holstein dairy herds in Isfahan were used. Six age periods: 1 to 30 d, 31 to 180 d, 181 to 365 d, 366 to 760 d, 1 to 450 d, and the full period 1 to 760 d were considered. Records of animals slaughtered or exported within a defined period were set to missing values, whereas their records were kept for preceding periods. A logistic regression model with effects of herd, year, season of birth, number of dam’s parity, calving ease, twin, group of sperm, and linear and quadratic form of birth weight as covariate were considered. Mortality rates were 2.17, 3.42, 1.98, 4.17, 8.2, and 12.4% for the six mentioned periods, respectively. In general, the parity of the dam had limited influence on mortality of the calves in older ages. No significant associations were found between mortality and sperm group. A significantly higher mortality for calves being born from difficult calving was found for the most of the age periods. Mortality rate during first mount of life were higher in calves born in autumn rather than winter. According to the current study, birth weight is important effect in survival of calves until first calving.