The head wagging is still odd but explainable by a few different ailments of which not many exonerate a bird from breeding stock status.
About roosters slipping off the back, no, that's definitely not the norm. A bung leg would be the likely cause. And unwilling or unhelpful hens, lol. You'd probably be surprised by the lengths a willing female will go to, in order to assist a male to mate when he can't do it without help. Routinely (in Australia anyway) you hear of cats and dogs getting pregnant through mesh, and you see cows with bulls half their size standing downhill of them so they can reach... Just stuff like that. But they have to like the male enough, or just be that bent on being a mother. Some female animals don't live for anything else, it's a burning priority, whereas others don't care much or at all.
About roosters slipping off the back, no, that's definitely not the norm. A bung leg would be the likely cause. And unwilling or unhelpful hens, lol. You'd probably be surprised by the lengths a willing female will go to, in order to assist a male to mate when he can't do it without help. Routinely (in Australia anyway) you hear of cats and dogs getting pregnant through mesh, and you see cows with bulls half their size standing downhill of them so they can reach... Just stuff like that. But they have to like the male enough, or just be that bent on being a mother. Some female animals don't live for anything else, it's a burning priority, whereas others don't care much or at all.