I’ve been caring for a kitten and would like to find it a permanent home. Am I allowed to give it to a
secular Jew, given the halachos involved with owning animals, that he would almost definitely transgress?
(Hilchos Shabbos, operating on it to make it infertile, feeding it before himself, etc.).
If it’s problematic, would it help if I declare it hefker and he then takes it or is that lifnei iver/otherwise problematic?
It is permitted to give the cat to the secular Jew, and you don’t have to be concerned that he will decide on his own to do something that he shouldn’t with it. This is because you are selling him a permitted item, and not something that is clear that he will sin with it. Therefore, if he decides to sin with it, that is his issue and you are not considered causing the sin that he will do.
Toldos Yitzchok (Yerushalmi Sheviis 5-3), Mishnas R’ Aron 1-3, Igros Moshe Y:D 1-72, Chazon Ish (Shviis) 12-9.