Until the late 1990s, captive Asiatic lions in Indian zoos were haphazardly interbred with African lions confiscated from circuses, leading to genetic pollution in the captive Asiatic lion stock. Once discovered, this led to the complete shutdown of the European and American endangered species breeding programs for Asiatic lions, as its founder animals were captive-bred Asiatic lions originally imported from India and were ascertained to be intraspecific hybrids of African and Asian lions. In North American zoos, several Indian-African lion crosses were inadvertently bred, and researchers noted that "the fecundity, reproductive success, and spermatozoal development improved dramatically."