In your comparison you want horses to have greater protection then cats & dogs.
Mandate NO KILL for dogs and cats and there will be a public outcry. How will they pay for ALL the unwanted animals.
On COTH alone there are some that find no problem in killing dogs or cats, for various reasons. Many find no problem that they have a killer dog, they say it is only natural. I have seen posted, that it's ok for their dog to kill the cat that strayed into their yards. Also locally to me someone kills two dogs because he said they were chasing his sheep. That is ok by the law. He lied, now its a minor offense.
We humans have come to accept killing in various forms for a wide spectrum or reasons.
Euthanasia is killing. We just put a pretty bow on it to make it acceptable.
Slaughter is what it is killing. Animals die.
So pick your poison, humans kill for various reasons, get over it.
Oh ... they sell crickets in pet stores as food for other animals.