A bull breeding one of his own heifers would mean the offspring would be 3/4 that bull's genetics. From what I've read that is too much, unless you are into true line breeding like Line 1 Herefords, and you may run into genetic problems.

I've been retaining heifers and a bull calf each year.  Breeding a bull calf to his half sisters keeps the parent bull or cow to 50% of the offspring's genetics which from what I've read is about as high as you want to go.   I move bulls around to make sure a bull does not breed his own heifer calves nor a retained bull breed his dam.

However breeding my best retained bull calf to his half sisters has so far worked very well producing some excellent cows and steers with no genetic problems so far after about 6 or 7 years of this.