Challenges to fertility in dairy cattle: from ovulation to the fetal stage of pregnancy

One critical determinant of fertility is the establishment and maintenance of pregnancy after insemination or embryo transfer. Pregnancy success is low in lactating dairy cows. Reduced fertility of the dairy female is only expressed in the lactational state but the magnitude of depression of fertility is not related to milk yield. Pregnancy failure occurs throughout gestation with the greatest frequency of pregnancy losses being in the period from fertilization to day 5-7 after insemination. Poor fertility in lactating cows represents, in part, failure of genetic selection for reproductive traits. In addition, the uterus of the lactating cow is less able to support embryonic and fetal development than the uterus of the non-lactating female. There is little evidence that the oocyte is compromised in lactating cows. Among the determinants of pregnancy success in lactating cows is progesterone secretion in the post-ovulatory period, environment of the ovulatory follicle during its terminal growth, energy balance, and amounts of specific nutrients in the diet. Progress in improving reproductive function of the lactating cow is being made and the historical decline in reproductive function is beginning to be reversed.