Forget that bulldog hood ornament. It's the Chihuahua that's the top dog in ads these days. Heinz Pet Products Co.'s ad for Nature's Recipe pet food touts its Group Specific Formulas, aimed at seven breed groups. Goldberg Moser O'Neill, San Francisco, created the ad featuring the mighty Chihuahua. Copywriter: Chuck Meehan. Art director: Matt Mowat.