Early Pregnancy Diagnosis in Bovines: Current Status and Future Directions

Table 1

Important events during the early embryonic period.

Days of pregnancy	Event
Days 0-1	Fertilization, single-cell embryo (zygote) in oviduct
Day 2	Early cleavages in the oviduct (up to 8 cell stages), activation of embryonic genome
Days 3-4	Embryo enters the uterus
Days 5-6	16–32 cell zona-enclosed embryo progressing into compact morula stage
Days 7-8	Formation of a blastocoele with differentiation of embryonic cells
Days 9-10	Blastocyst expansion and hatching from the zona pellucid
Days 11–15	Blastocyst elongation from a tubular to a filamentous structure
Days 14–19	Maternal recognition of pregnancy
Days 19-20	Implantation begins
Day 21	Caruncles-cotyledons appear
Days 22–41	Implantation progresses
Day 42	Implantation completed

Compiled from available information (Morris and Diskin, 2008 [3]; Hafez, 1993 [4]).