We often get -20c here in Bulgaria over winter and our birds are all in unheated accommodation.... mainly it's our Indian Runner duck eggs that get frozen 'cos quite a few of them seem to drop their eggs just anywhere, rather than in a nest box or some nice warm
straw! We have cooked them, but usually we give them as a morning treat to one of the pigs, or just crumble them "as is" into a bowl of bran or mash for the birds - who happily consume them.