If you will spit it out, you can’t make a bracha because you are not eating.
It would be good to swallow a bit and have intent to enjoy it; then you would make a bracha.
It is indeed assur to eat before feeding animals that you are responsible for, such as your pet dog, but I am not sure if this issur would apply to a very small amount of food (a drink is definitely allowed). Perhaps you would be allowed to eat if the eating is necessary in order to feed the dog, like in your case, where you need to chew the dog’s food before feeding it to the dog.