Infertility associated with the duration of luteal phase in postpartum cows

After first postpartum ovulation most cows have a short luteal phase due to a premature secretion of PGF2a from the uterus. Pregnancy rate in estrous cycles with short luteal phases is essentially nil. The lack of exposure of the uterus to P4 and estrogen prior to first postpartum ovulation decreases the concentration of P4 receptors and up regulates oxytocin receptors. The inadequate number of P4 receptors and presence of endometrial oxytocin receptors earlier in cows with short than normal luteal phases allows premature release of PGF2a and the resultant regression of the CL. During luteolysis, uterine and luteal PGF2a cause death of the embryos mainly during the transition from morula to blastocyst when the embryos are more susceptible to embryotoxic effect.