This sounds a lot like why horse mares will eat the placenta from their foals after giving birth. Foals are born able to run, but they're nowhere near as strong as a mature horse.
I was under the impression they ate it because of all the vital nutrients that the placenta had, but I dont think anyone had conclusive evidence except in an evolutionary biology hand-wavy way.
Whence do you suppose the nutrients in a placenta originate?
Actually everything in this thread is a just-so story. It's pretty silly to pick out one specific rare behavior as even relevant to evolutionary fitness. How would any of this be tested?
I dunno, if you have been gestating a foal, you might be a little undernourished at the end of the process, so a placenta's worth of nutrients might then be "vital."