Oh, look what I found:

Initially the primary method of breeding giant pandas in captivity was by artificial insemination, as they seemed to lose their interest in mating once they were captured.[66] This led some scientists to try extreme methods such as showing them videos of giant pandas mating[67] and giving the males Viagra.[68] Only recently have researchers started having success with captive breeding programs, and they have now determined that giant pandas have comparable breeding to some populations of the American black bear, a thriving bear family. The current reproductive rate is considered one young every two years.[12][24]