I was told that the success rate of breeding your own boxer is quite low, is this true? and how come?
Well, I'm not exactly sure what this means. Breeding your own Boxer as compared to breeding someone else's? In that case, I think you'd be more successful breeding your own!
"Success rate" meaning what, in this case? That the bitch will "take" (conceive puppies)? That the bitch will go full-term and deliver live puppies? That the puppies will survive past the first few weeks? That they will turn out to be good representatives of the breed?
Actually, it doesn't really matter. The "success rate" for all of these factors depends a great deal on the knowledge and experience of the breeder and the health and conformation of the sire and dam. Boxers are not "hard" to breed, although they are sometimes prone to thyroid issues which can affect fertility and reproduction. C-sections are not uncommon but not routine, and those due to primary uterine inertia (as opposed to secondary or a 'stuck' puppy) tend to run in lines. Puppy mortality in general is not high, although there are always exceptions - but again, the more experienced/knowledgeable the breeder, the better the chances of puppy survival. Having parents that are good breed examples tends to produce puppies that are the same (or, ideally, better

) - one of the toughest things, especially for new breeders, is objectively evaluating your bitch and finding her faults, so that you can match her to the best stud dog who is strong where she is weak. The goal of breeding should always be to improve with each generation, and kennel blindness or lack of knowledge often interferes with this!