“Charlie, how in the world did you get that P’sak? It doesn’t make sense.”
I asked my rabbi; he wasn’t sure so he checked with HIS poskim. I was frankly stunned by the responsum (as was another rabbi when I mentioned it). The logic was that animals exist to serve humans and if their going into heat was a big problem for the humans (and if you have ever seen a female cat in heat you will know what that means) then it is permissible to have it sterilized.
” If you did it yourself it’s a clear Lav “
I would never do that on something like that. I had expected to be told to sell the cat to a non-Jew for the purpose of the operation, and then to buy it back.
“and as far as I know the vast majority (if not all) the Poskim hold that Sirus is Assur for a Goy also.”
I don’t think you are correct on that; we talk a lot about the seven Noachide laws and this would be an eighth Noachide law. It certainly does not appear to be the majority opinion in the gemara. And the reason given in the gemara is pru urvu, which is not one of the seven Noachide commandments (even though it was given to Adam Rishon).