My daughter has been diagnosed with precocious puberty. Could she have started her period so early because she drank milk containing bovine growth hormone?
I strongly doubt that. The only external compounds clearly implicated in girls' early puberty are estrogens. Moreover, when human growth hormone is intentionally given to children to increase their heights (in doses far higher than your daughter could accidentally consume) precocious puberty has not been a problem. You are right to be concerned about the chemicals used by agribusiness; but from bovine growth hormone, I would be more concerned about cancer.
A Harvard study published in the October 13, 2006 Annals of Internal Medicine of more than 90,000 young women found that those who ate 4.5 ounces a day or more of red meat had about twice the chance of developing hormone receptor positive breast cancer before menopause did their peers who ate less meat. Because these tumors were hormone-sensitive tumors, the researchers propose that the added hormones in conventional beef may be the cause.