I wonder how often this happens? This year we have a grandma, daughter and granddaughter, and a mom and daughter. So essentially two maternal lines. The first set all came into heat on the same day and were bred. A few weeks later the second set came into heat on the same day. (We didn't breed that same cycle, 'cause hubby was out of town.) Next cycle those two came into heat again together. (Yesterday and today. We bred them.) These are Nigerian Dwarves. Does this happen often?