Table 2.

Key events in sheep and cattle embryos/foetuses with particular emphasis on nervous and immune systems. Compiled from [87,88,89,90,91,92,93].

Event	Timing in Cow (dpc)	Timing in Sheep (dpc)
Blastocyst hatching from zona pellucida	9	9
Elongation of the blastocyst, establishment of the primitive streak, emergence of the notochord	17–18	13–14
Appearance of neural folds, closure of the neural groove	17–19	15–16
Implantation begins	16–19	15–18
Neurula	20–21	17
Neural tube complete; optic and otic vesicles present	21–23	19–20
Placentation begins	22–23	17–22
Three brain vesicles visible	24–25	17
Placentoma are detectable	32–36	21
Lymphoid development of the thymus	42	36
Spleen development	55	43–44
Peripheral lymph nodes	60	45
IgM containing cells	59	65
Myelin sheath acquisition (starting)	60	54–63
IgG containing cells	145	87

With dpc, the days post coitum; IgM, immunoglobin M; IgG, immunoglobin G