Final answer:
Listeria monocytogenes and rubella virus are two pathogens that can cross the placental barrier and are commonly known to cause early embryonic death in bovines.
Step-by-step explanation:
The two bovine pathogens commonly known to cause early embryonic death are Listeria monocytogenes and the rubella virus. Listeria monocytogenes is a gram-positive bacterium capable of crossing the blood-placental barrier, leading to a risk of spontaneous abortion. Rubella virus, known for causing German measles in adults, can be devastating if transmitted to the embryo, potentially resulting in fetal death or a variety of severe birth defects.