kaywoodie,
The meat of all the nilgai I've taken has been aged for a while, which makes considerable difference in chewability! One was aged in the cooler a butcher shop in Texas before being shipped to me; the others were aged in the coolers I brought them home in via airlines.
Depending on the animal, we've aged game up to 3 weeks before butchering and freezing. That long can make a BIG difference even in old bucks and bulls!
