I don't know you can affect gender, that's the stallion not the moon I reckon too
but there definitely seems to be a larger number of births around full moon so could well be they were conceived then too, who knows.
I had two foals the same night on a full moon in May 2009 - one before midnight the other at 2-3am which I found just as I went to check on the foal I'd seen born a few hours before. Was one of each tho, filly before midnight, colt after, so I don't think I would hold too much faith in the conception/gender relationship with the moon phase..