Duck eggs won't hatch

[jgiajnorio]

Hi there, I have a Muscovy hen and drake starting their third summer, we have had 4 batches of eggs since we got the pair, and non have hatch. She will sit on them all day. Last season you abandon or broke most. This last batch she was really good and kept almost all of them under her the whole time. After a month we candles the eggs and nothing. They all seemed to be undeveloped.

Any thoughts...we are starting to believe the drake is the problem. Could he be sterile?