Each flock is unique and has its own dynamics. We keep them in a lot of different ways. It’s very possible that your cockerel is keeping every pullet in your flock fertile, but the only way to be sure the ones you want to hatch from are fertile is to open their eggs and look for the bull’s eye. This thread has more photos and some discussion on that. If you crack an egg and don’t see anything try to gently turn it over. I use a spoon but be gentle.
Fertile Egg Photos
A rooster or cockerel does not keep a little black book where he notes, “OK that one is fertile, I need to go to the next one.” Mating is random. He may have favorites and some females hang out with him more than others do so some are more likely to be mated than others. That’s where flock dynamics come in. When they mate the sperm is stored in a special container near where the egg starts its journey through the hen’s internal egg making factory. The sperm stays viable for quite a while, I count on two weeks, not three, but whichever it is your cockerel does not need to mate with a pullet that often to keep her eggs fertile.
If you find that some of the eggs you want to hatch are not fertile, penning him up with the specific pullets would increase the chance of a random mating. There is a trick to improving those odds. I’ve noticed that if I remove my rooster from the flock for a while, say 15 minutes or more, when I put him back he usually mates with a hen just to show it’s still his flock and that he is in charge. That’s still random but it can help. You can also try removing a specific pullet for a while and putting her back. Sometimes the rooster will mate with her to show she’s still one of his girls. It has to do with dominance more than pure sex but if it gets the results you want…..
I have hatched pullet eggs before, not the ones they lay in the first few days but say after they have been laying about a month. They are still fairly small compared to what they will eventually be but significantly bigger than the first few eggs laid. What I’ve found is that many of them will hatch but my hatch rate is not as good as with the larger eggs from older pullets or hens. I have had a few hatches where the rate of pullet eggs set to chicks hatched was 80% but 50% is a lot more normal. Some hatches have been horrible.
I’ve also noticed that the survival rate of the chicks hatched is lower than the ones hatched from larger eggs. I don’t have any numbers on that. I don’t often lose a lot chick after they hatch but I’ve noticed that most of the ones I lose are from those small pullet eggs. If they make it past the first two weeks they are in pretty good shape.
You can hatch pullet eggs but your rate of success will be better if you can be patient and wait on larger eggs.
Something I find funny is that Aristotle had a different view on the round versus pointy question. He thought pullets came from pointy eggs while cockerels came from round eggs. This is not meant to discourage you from participating in that thread, I think it would be interesting and fun. I just think it’s interesting how long this type of question has been around. Good luck on getting pullets.