Every boa in my care has gone straight to rats soon after birth. As far as frequency and size of prey, it is debatable, what I did was allow the specimen to decide, my male was not big on feeding so he grew a bit slower and only ate about every 10 days or so on average. He is now a well proportioned 6ft animal. My female was my little garbage disposal and thus skyrocketed in growth, sometimes feeding every 6 day. She is a beautiful 8ft with fine muscle tone and a nice "square" shape, as you will hear some refer to it. The goal is to produce a nice well balanced physique that reflects a well fed but at the same time fit animal.