[header] How to know if a male dog is fertile [title] Make sure that your dog is old enough to breed. [step] A male dog that is too young will not be able to reproduce. A male dog usually reaches sexual maturity when they are over a year old, however they usually begin puberty when they are six months to eight months old. 
They can impregnate a female dog from the point of puberty on. [substeps] If you want to use your dog for breeding when it is at its maximum fertility, wait until it is at least a year and a half old.