It is my impression that many (most?) breeders use artificial insemination these days?? Some breeders have told me that it is more 'safe' because of the size of the male (he might harm the female during the mating). Well, large animals have been able to mate naturally during centuries: bulls with cows, elephants, ice-bears etc. - and also mastines . For those of you who let your mastines mate in the natural way: Great! Keep on doing that
Sally, it'd be better not to compair bulls and elefant-bulls with male-dogs (be it of a large or a small breed), because these animals don't have the natural habit to lift one hind leg over the back of the female (such as Tarquin in the picture) and then turn "ass-to-ass". The only other animals that have this habits (such as foxes) are smaller. The stories I hear is that breeders are afraid of the bitch damaging/ ruining/ destroying the stud by trying to escape this "tie" at this critical moment . Yet, I agree that natural mating of dogs is a positive thing.
Agree with Suskewitz and would add: some stud-owners don´t want spend time of his stud allowing the natural way. Another reason I heard was to prevent sexual deseases (?).