This is very possible especially in British heifers. Shorthorns are one of the earliest breeds to reach puberty. I remember reading a study done by U of Montana a few years ago, and it reported on average Shorthorn X heifers reached puberty about 2 weeks before Angus, 3-4 weeks before Hereford, and about 6 weeks before Continental breeds. As I mentioned, this was a few years ago, and I do not know if it hold true for more recent genetics in each breed. I know of many breeders in these parts who sort their cows with bull calves to one pasture, and those with heifer calves to another pasture when the calves are about 5 months old. Over the past number of years I have seen several heifers cycle before weaning. I had one calve at 13.5 months a few years ago, and she calved on her own. By the time, I saw she was starting to make some udder, she was too far along to abort so I worried about her for a few months. She had a bull calf and did a great job of raising him and he sold for $3500 to a breeder in Eastern Canada.
Jim Leachman from Leachman Cattle Co used to say that if he could only select replacements by using one trait, he would select them all by their age at puberty.
