Is it acceptable to spay a pet female dog, or is there a prohibition against neutering a female dog like that of a male dog?
In the eighth volume of Bemareh Habazak (soon to be published by Eretz Hemdah) will appear a detailed teshuva regarding neutering and spaying with all the sources. For now I will copy just the conclusions pertaining to this question. The question was regarding running a veterinary school so the answer refers to lectures and student:
Demonstration by Jewish lecturers or hands-on training by Jewish students of sterilization of animals is permitted regarding male animals only if it is done through medication which doesn't damage, even indirectly, the reproductive organs themselves , but just depresses the function of sexual hormones or reduces the quality of the semen , and as a result a female which will mate with this male will not become pregnant. It is preferable if the sterilization done in this context be effective only temporarily .
In the above demonstration or training, in regards to a female animal , sterilization by medication is permitted even if it will have a permanent effect on the ability to reproduce .
However, neutering or spaying, which damage the animal’s reproductive organs, is prohibited, both regarding males and females .
In regards to a male, pharmacological treatment that causes permanent sterilization (and the effects can be seen on the external reproductive organs) is prohibited , and damage to the organs by chemical treatment, radiation, or stopping the blood flow, which causes a degeneration of the (external) reproductive system, is also prohibited .
Surgery or any other form of prohibited sterilization is prohibited even if it can be rectified by further surgery .
As mentioned above, the institute must allow the students to complete their studies without performing any of the prohibited forms of sterilization, and this must be advertized so as not to cause students to falter in this respect.
Generally, these guidelines apply also to non-Jewish students or lecturers who act for the benefit of or by instruction of Jews .
Regarding non-Jewish students or lecturers, pharmacological treatment that depresses the sexual hormones or damages the quality of the semen is permitted even if the sterilization is permanent . One may also be lenient regarding them and permit spaying a female , and also permit surgically damaging the semen tubes that are in the body of a male, not in the external organs .
So too, one may be lenient regarding non-Jewish students and lecturers in regards to indirect sterilization, such as one done by chemical treatment, radiation, or stopping the blood flow, thus causing the degeneration of the reproductive system, even if the sterilization is permanent and even regarding male animals .