Line breeding

I breed Triggs for coyote & field trial & hunt hard in the winter & have placed at the national level. I normally have two litters a year from my best stock & run them all so I can judge results of the breeding program. Many people do believe in line breeding at that level. Sometimes I have seen very experienced breeders who do breed say sister on brother & have sucess the first time, then the time or two they breed the offspring they get into trouble. It sometimes seems they are very good or maybe totally useless or anything in between. I personally dont believe in it & feel why should I do it. They say that if you do that, then both parents had better be very very good because of the likely hood of bad traits being emphasized. The one thing it does is give you unblieveable consistency, good or bad. This is fine if you have a purbred line with a history of conistency but when you are crossing two different lines where does this come in. Thats mine opinion anyway for what its worth. I do have experience with breeding other livestock as well. I do know that if you cross two different breeds, be it dogs, cattle, horses or even chickens the first cross is usually very healthy & often very tough. I think the fact that they are completley different genes means they seem to get the best of both, thats my oppinion anyway.