I have a few hereford heifers. Bred to low birth weight angus bull in March. I took possession of them in April. My black bull (14 months old) has been observed by myself to breed one of them as late as four days ago. Is this a sure sign that the cow was not pregnant or or what. I thought they wouldn't breed if the cow is pregnant. New to this, thanks for any and all comments, love this board!