Tested this in arena using butcher command. Not sure if it would be different in fortress mode, but...
Groundhog 7: Very fat, enormous overall (Should be more fat)
Groundhog 8: Very muscular, gigantic overall (should be more meat)
Groundhog 9 & 10: No descriptors
After a quick slaughter by a godlike dwarf in the highest quality gear (using a spear so as to not mutilate the goods), all bled to death
Groundhog 7: yielded skin, 6 units of fat, 6 units of meat, 4 units of bone, one unit of prepared intestines, one skull
Groundhog 8: yielded skin, 6 units of fat, 6 units of meat, 4 units of bone, one unit of prepped intestines, one skull
Groundhog 9: yielded skin, 6 units of fat, 6 units of meat, 4 units of bone, one unit of prepped intestines, one skull
Groundhog 10: Yielded skin, 6 fat, 6 meat, 4 bone, NO PREPARED INTESTINES, and one skull
both groundhog 8 and groundhog 10 had their stomach torn by an assault, so no idea on what causes organs to be available for eating or not.
However, this is post-death butchering, and death also makes the descriptors disappear, apparently. (e.g. the upper body is missing compared to eye color). I didn't check the post-death descriptors, stupidly enough, so maybe something there would've told me about it.
Testing on tame animals butchered with death-by-butchery may be required, but personally I think it doesn't matter. It should be IMO, but it doesn't seem personal characteristics affect butcher results.
Personally, I'm more interested in what causes certain organs to be available for preparation/eating.
Groundhog 8 suffered neck, right front paw (bone, ligament, and tendon x2), lower body (stomach and muscle), lower body (muscle and lower spine nervous tissue), and left front leg (bone and tendon) injuries
Groundhog 10 suffered lower body (muscle and stomach), right front leg (bone, sensory nerve, and tendon), upper body (left lung, trouble breathing), left rear leg (bone and tendon), upper body (muscle, upper spine nervous tissue, and tendon), and left front leg (bone, artery opened, tendon) injuries
Maybe arteries have something to do with it? That's my best guess. >_>