Underbite is definitely an in-bred defect! I had a friend that ran a trail ride concession for a resort close to where he lived. about 1998, they decided they wqanted to offer a cattle drive experience, so he bought about 10 LH cows and calves, and a bull. I and a couple of other friends, spent a week driving them from the resort to his place ( all through woods and fields...never had to get on a road) til we got them broke to where they'd almost do it themselves Fast forward to 2007, when he and I started this hay business, buying truck loads of 2 3 x3 and 4 x4 bales of alfalfa, and selling it to equine facilities in north and west Ga. Well , his LH pasture had about 40 head in it. The man had never culled...never cut a bull or sold any of them. He'd just bury them in his horse and dog graveyard when they died. There was grand fathers and fathers and sons and grandsons, all breeding mommas and grandmommas and daughters and sisters, etc. The place was full of calves and yearlings, that were dwarfs, and had sever underbites! I think they all had Down's Syndrone or something, too. They acted retarded! Only thing normal LH size on them would be their horns. They reminded me of that Jerry Lewis character that had the severe overbite. Another thing the in-breeding did, was give them all long shaggy forelocks, like a Beatles haircut!Travir, I assume that you check all of your calves for underbite, by lifting their lips and checking whether the lower incisors contact the dental pad? Underbite is difficult to see without doing that.