I'm a food-animal veterinarian/veterinary pathologist. I know more than a little bit about genetics, genetic defects, inbreeding suppression, etc., - so I'm aware that if an undesirable gene is present, breeding closely-related individuals will increase the likelihood that it will be expressed - but at the same time, inbreeding/linebreeding can be used to concentrate the genes that code for desirable traits. It's how ALL of the breeds we now know were originally developed.
In the vast majority of instances, whether you're a commercial or purebred operation, there's little downside to breeding a bull back to his daughters - if you like the bull and the traits you selected him for, and he's passed them on to his daughters, you're just maximizing those desirables by practicing some in-herd inbreeding. Really, outside of the possibility of recessive defects, the only significant downside is from narrow-minded people who might look at the pedigree and get their panties in a wad about (gasp!) 'inbreeding', and shy away from what you've produced.
If you look at pedigrees for many bulls in many breed associations, you'll see specific animals or family lines appearing time after time. How many Angus bulls have EXT, 6807, Scotch Cap, etc. multiple times in their ancestry? How about 600U, Black Mick, Black Irish Kansas, Siegfried, Doubletime and now, Dream On, etc., in the Simmental breed?
I think it's CRAZY for a small commercial beef producer with just a few cows who may only need one bull at a time, to be buying a new bull every two years - you're not 'getting your money's worth' out of that bull purchase, and you don't really know for sure what you have(or had) before you get rid of him. If he's good, he's worth breeding back to his daughters; if he's not, then put some wheels under him and bring in something different.
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