Q. Re- questions 2657,2658 above – Could there a better way to spay a cat, that won’t involve all the above issues?
A. There may be another procedure for sterilization mentioned in the Talmud and Poskim know as “Kos shel Ikrin,” or drinking a potion that can render a woman, man or animal infertile. This method of sterilization is only forbidden for males and is permitted for females.(See Igrois Moshe E.H. 1: 13, Teshuvos Vehanhogos C.M. 887).  Some hold that this form of sterilization for males is forbidden on a Biblical level, while others maintain that it is only Rabbinically forbidden.
Zeutering is the Non-Surgical Alternative to Neutering. Zeuterin is a non-surgical sterilant for male dogs delivered via intratesticular injection. The active ingredient is zinc gluconate neutralized with arginine. The formulation causes permanent sterility in one treatment.
As of this time, there does not seem to be a practical drug that would render female animals totally infertile and an alternative to spaying. One should consult a veterinary on that respect. It is likely that eventually one will be developed and approved.
Bemare Habazak (6: 77) permits the use of hormonal inhibitors, in need even for male dogs, and on the onset for female animals.
Horav Shlomo Miller’s Shlit’a opinion is similar.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit’a