I think the bull definitely has an impact on gestation length. We've been using BR Midland for several years and have never had a cow go 283 days. We've had some born two weeks earlier. They're very small, of course, when born that early. I know an ABS rep who always used GT Maximum on cows if they missed on the first AI. He said MAX was a short gestation bull and by using him he could keep the cows in a tighter calving period. Our first Midland heifer calved ten days early yesterday. We generally get heifers up about two weeks before their due date, but we'll get those other Midland girls up sooner than that....just in case. On the other hand, Woodhill Foresight calves seem to take the full 283 days. In fact, yesterday we were about to turn a cow back into the herd, thinking she wasn't AI bred, when she started paying a lot of attention to another newborn. So we left her alone and she calved at 286 days, a heifer at that.