That depends on for what you are breeding. If it is for meat and not for intelligence, then in the big scheme of things it is not a problem. Even if you want to play worst case scenario and believe that (as is the case for humans) each individual has 8% lethal recessive genes, and assume both individuals pass all at once, that means that roughly 15% of the piglets wont survive infancy due to genetic problems, that's still 85%. If you are homesteading and not selling to commercial markets, that's still good production (6 piglets instead of 7). Also assuming you are letting the sows feed the piglets, the piglets will grow a little faster if they have less competition for food. Now the resulting pigs aren't going to be discussing the theory of relativity in relation to quantum mechanics as influenced by fractal theory, but then they are intended for sausage, now aren't they.