They say that the older the tup (or bull) gets, the more male offspring he sires.
We did measure one year on the moorland farm, and there was a very slight correlation, but not statistically significant on the numbers we had.
Personally I wonder whether it's more that if you have a favourite tup or bull, you don't keep his daughters the first year or two, so that you can keep him longer. Then when you are ready to keep some of his daughters on, he seems to throw nothing but males!
