Complex sentence: In addition to the differing genitalia, bulls tend to be larger than cows of the same breed, and to have heavier (although not necessarily longer) horns, among those breeds that have horns.
Split into simpler sentences: In addition to the differing genitalia, bulls tend to be larger than cows of the same breed. The horns of the bull tend to be thicker than those of the cow, but not as long, among those breeds that have horns.