Risk factors associated with reproductive performance in Japanese dairy cows: Vaginal discharge with flecks of pus or calving abnormality extend time to pregnancy

The present study aimed to determine possible risk factors affecting reproductive performance, especially time taken to establish pregnancy in dairy cows, using Cox's proportional hazard model. The data were collected from 154 Holstein Friesian cows (199 lactations). Cows diagnosed with a vaginal discharge score (VDS) of one or calving abnormality showed significantly delayed pregnancy: hazard ratio (HR)=0.654 (95% confidence interval [CI]: 0.436-0.983; P=0.041) and HR=0.457 (95% CI: 0.270-0.774; P=0.004), respectively. Our study suggested that the occurrence of VDS of one or calving abnormality might be possible risk factors increasing the number of days open and affecting reproductive performance in dairy cows.