evaluation of none genetic and genetic factors affecting on stillbirth in iranian holstein dairy cattle

stillbirth is defined as a calf death just prior to, during, or within 24 to 48 h of parturition. the exact cause of calf death in dairy cows in this period of time is unknown. the objective of this study was to investigate about the effective factors on stillbirth and also to estimate some of the genetic parameters in iranian dairy holsteins. data in the first and second lactation that have been collected from 1998 to 2007 were analyzed separately and a threshold model was used to analyze every calving data. the effects of milk-2x, age at calving, herd-year-season of calving and also sex of calf on stillbirth rate were all statistically significant. male calves showed significantly more stillbirth rate than female calves. the heritability’s for stillbirth in the first- and in the second lactation were estimated 0.025 and 0.01, respectively. after classification of first- and second lactation cows for milk yield levels and age at calving, the results showed that stillbirth was higher for cows with high milk yield potential and the older cows have more stillbirth than the younger ones.