I have some heifers that are about 800 lbs. They are black angus and hrreford. The actual birth date is unknown. I was told they were 6 months old when I bought them in October but have had no contact with the seller since. How big should they be before I breed them. My neighbor uses jersey bulls to breed his charolais heifers for low birthweight but I was thinking using a mini hereford bull for the first calf with the angus. I want to see if they will produce black baldies. Any advice?