The phrase "less fillers" means having less unnecessary or unimportant things included. It suggests having more of what is essential and valuable. Full definition
Dogs that eat less fillers in their foods go to the bathroom much less by amount, translating into less waste and less time spent picking up waste. (premierpetrelocation.com)
For example, giving your pet a high quality pet food that contain less fillers will help reduce the amount of times the pet has to eliminate. (blog.petmeds.com)
The lack of grain, corn or wheat means less fillers or empty calories. (alliswellpets.com)