Both my DD's had urates in the first few days as my milk takes up to 5 days to come in. Both of them lost just over 10% of their weight as well. My midwives weren't concerned so much about the urates but the weight loss, but they never mentioned formula just extra expressing. Once my milk came in though, the urates disappeared. If your middies aren't concerned, and bub is as active as you would expect a newborn to be (waking for feeds etc), don't worry. Just bring him to the breast often so he gets that colostrum and stimulates your supply.