We have 3 billies now..gluttons for punishment did I hear you say?..and we for us the best situation is to let them all have a wife and a concubine or two! That way they are not lonely and the girls who are too young or too old are safe from their attentions. They sorted it out for themselves who wanted to stay with whom and some definitely couldn't get out quick enough after their brief nuptials. No reason why they shouldn't have their preferences I'm sure. We have obviously kept a note of when they are likely to kid and will take them out to give them a bit of peace when they are imminent. I'm not saying everybody would agree with our way of doing things but , for us, this is a nice happy way to run our herd.
The main problems with letting a billy run whith the whole herd full-time (and we have done it that way too!) are
for one thing it's difficult to keep the youngsters and the geriatrics away from the randy little devils, plus, if you are milking it WILL smell and taste rather like a billy smells (an aquired taste I think) , they will mate again straight after kidding so your poor girls will be worn out and finally, you will have no real idea of when to expect kids. But..you will have a tired and happy billy!!