Why a cow hunt? I find hunting for bulls to be easier. You can call them in close, and they're alone. Cows are generally herded up.
It sounds like gramps will be doing just the shooting. Get him a nice bull. Cows are for meat hunters.
edit..I forgot i'm speaking for myself who just takes close shots. I suppose a cow would be easy if you take long shots, but I would still think he'd be more thrilled with a bull.