The active period for the implant is from 8 mths to 4 years (Reported in Australia). Baldness is the least of the problems that may occur, it is known that the hormones (estrogens/testosterone) can be can be elevated without external symptoms and that when the disease does recur it often comes back very quickly with the consequent risk of hyperplasia/neoplasia. The general opinion seems to be to re-implant at 12 mths regardless. I personally keep a close eye on my two for any signs at all from 8 mths and have a new implant at 12 months, It is not expensive and even if the original implant is still active no harm will be done with a second implant (up to 10 times correct dose has been given to dogs with no harmful effects). Tony (not a vet), Sugar and Suki. In memory of Sally and Sue. [Posted in FML 6606]