UIUC 獸醫學院的問答
http://vetmed.illinois.edu/petcolumns/petcols_article_page.php?OLDPETCOLID=64
俄亥俄州立大學獸醫學院的文章,男狗6-12個月就能生殖了
http://vet.osu.edu/vmc/spay-neuter-surgery
Most male dogs and cats are ready and willing to reproduce by the time they are six to 12 months of age. They are able to breed consistently throughout the year or whenever they are exposed to a receptive female. Both male dogs and cats are prone to wander in search of romance and find themselves exposed to fighting with another animals or dangers such as cars.