At our Shabbos table the following question came up: Is one allowed to mafkir a dog they own? (The thinking why it might be assur: Tzaar ba’alei chaim … you’re leaving the animal without a home and to ‘fend for itself’.)
If you can send a source with the answer it’d be greatly appreciated.
An interesting source for this is the Gemara in Chulin (7b), where Rabbi Pinchas b. Yair objects to the suggestion of being mafkir animals, for the reason that the animals might cause damage. Following this, he objects to the suggestion of castration, because of the pain it causes to the animals.
This Gemara cannot be a direct proof for the question; the Gemara refers to mules, which could presumably fend for themselves, and the principle cannot be applied to dogs, who might not damage others, but might also not be able to fend for themselves.
However, we see from the Gemara that on a level of lifnim mi-shuras ha-din, one must be wary of causing pain to animals, even where there is human need to do so. Me-ikar ha-din, it is permitted to do so, as Tosafos write in Avodah Zarah.
Therefore, it would appear that if the owner has a personal need to be mafkir the animal, it is permitted to do so, yet lifnim mi-shuras ha-din it is better to refrain from this, where the animal will come to inevitable harm.