Thanks that is useful information and greatly reduces my typing. That is a rooster, not a juvenile.
For a successful mating he needs to be able to stand in her when she squats, grab the back of her head (her signal to raise her tail up out of the way to give a clear target), and touch vents. Can you better describe what you see as unsuccessful about this mating? It sounds like he is trying but something is going wrong. Is the hen resisting or can he just not do it?
I don't know how thick Seramas feathers are. Some breeders of thick feathered breeds like cochin or orpington have to trim the vent feathers to get them out of the way of the rooster hitting the target. Certainly not all of them, but some.
Was that just one egg or have you had others also not fertile? One incident does not a trend make. If this is just one trial I'd check some others.
You did not say that this hen hatched her own eggs last year?
I've run out of ideas. Some are just not fertile. You may need to replace him.
Good luck!
