The first problem with the show is the obvious ethical issues. You can't beat up animals, even if it's sweet. An animal can't tell us if it wants to box or not, but I'm not sure why we care. I know enough about talking kangaroos to know that the first animal who can consent to a boxing match is going to be a fucking asshole.
The second problem with the show is that the only thing most animals know how to do on cue and with any enthusiasm is fight to the death or impregnate a surprised chicken. When you take those off the table you're left with a tug-of-war or maybe a race or something. The producers tried their best to come up with events, but the main reason most animals are sandwiches is because they suck at everything. Their competitions were things like a hot dog eating contest against a bear, an obstacle course race between a Navy SEAL and an ape, and 44 dwarves vs. an elephant in an airplane pulling showdown. Incidentally, if I had a show about men fighting animals and animal rights groups and uncooperative kangaroos ruined all my good ideas, 44 dwarves pulling an airplane against an elephant is exactly how I would tell everyone to screw themselves.
The producers had completely given up by the time they put an Olympic gymnast against an orangutan in a hanging-from-a-bar motionless challenge. It was about as compelling as watching someone die in a plastic bag against a goldfish. The contest went on for several boring minutes, and in an outcome too predictable to see coming, the ape wet its pants and lost interest. Humans! Humans! Humans! Honestly, I would have felt sadder for the orangutan if I was watching it lose a pistol duel.