To get a license for your pet, it MUST be spayed/neutered. That way it cuts down on unwanted pregnancies. Of its older than 6 months, the probability of unwanted pups/kittens is greater. So you have to pay more for license. It's more of a penalty for not taking care of it when your pet couldn't have pups/kittens.
The higher prices im sure is a penalty for not doing it when they were younger. Also as far as having a higher dog license price if the dogs are intact well that's because a dog that is intact is a lot more trouble especially if they get loose. A dog who is fixed causes less issues
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