It is extracted by a special process from the colostrum. Since there is a patent which greatly limits anyone's ability perform this extraction, many companies without access to that patent have started claiming immune-system building values to the colostrum itself. Transfer factors are less than one part in a thousand of colostrum. Colostrum is mother's milk during the first few days of breastfeeding. That is a dangerous lie.
Babies are at risk without breast fed milk to transfer of immunity from the mother.
This is a massive source of technical information about a substance which is starting to revolutionize health care.