I've never heard that it was necessary for a man to eat the afterbirth
to enable him to lactate...
All it takes, or so I have always been told, is an actual desire to feed a
baby, and constant practice.
Lactation is very much a supply and demand operation. In a mother, the process
begins with certain birth related hormones, certainly, but if no child
suckles, milk production ceases quite quickly. When the infant drinks more,
the milk ducts produce more, and visa versa.
All a father (or other interested man) needs to produce milk is the want,
and the opportunity. If the baby is getting enough food to avoid dying for the
week or so it takes for lactation to begin, he can feed it entirely
satisfactorily from there on, and experience all the fun of breast feeding