If I remember correctly at some point herding brahmin did hail about 75 EXP, but I could be wrong about this.
If you don't want people to herd and kill, though, I would suggest tamed brahmin give no EXP for kills.
Edit: Also, I'm not sure if this is already available to you, but there's a butcher in modoc, anyone who has the guts can get their cow butchered in exchange for some money.