[moiraz]

This is the explanation I've got (partially quoted) from http://www.islam-qa.com with regard to fixing by means of neutering the cat.

Preventing your cat from reproducing is preventing a natural process that Allaah has created in it. Undoubtedly the rulings on animals are not as serious as in the case of humans, but this does not mean violating the rights of the creation of Allaah.

If this operation will cause harm, or it will cause complications for the cat, then it is not permissible. The prohibition against causing harm is general and includes harm against both humans and animals. There follow some of the ahaadeeth that indicate this:

It was narrated from Ibn ‘Umar (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “A woman entered Hell because of a cat which she tied up and did not feed, nor did she allow it to eat of the vermin of the earth.”

The vermin of the earth means mice, etc.

(Narrated by al-Bukhaari, 3140; Muslim, 2242. There is also a similar report from Abu Hurayrah).

It was narrated from Jaabir ibn ‘Abd-Allaah that a donkey whose face had been branded passed by the Prophet (peace and blessings of Allaah be upon him), and he said, “May Allaah curse the one who branded him.”

(Narrated by Muslim, 2217).

The scholars differed concerning the neutering of non-humans:

The Hanafis said that there is nothing wrong with neutering animals, because that benefits both the animals and humans.

The Maalikis said that it is permissible to neuter animals whose meat may be eaten, and it is not makrooh, because that makes the meat better.

The Shaafa’is made a distinction between animals whose meat is eaten and others. They said that it is permissible to neuter animals when they are small if they are animals whose meat is eaten, but it is haraam in other cases. They also stipulated the condition that this neutering should not cause the animal’s death.

As for the Hanbalis, it is permissible in their view to neuter sheep because that makes the meat better, but it was said that it is makrooh in the case of horses etc.

Imam Ahmad said: I do not like for a man to neuter anything, rather that is makrooh because of the prohibition on causing pain to animals.

See al-Majmoo’ 6/155; al-Adab al-Shar’iyyah, 3/144, 145; al-Fataawa al-Hindiyyah, 5/358)

There is also a comment on neutering cats: “If neutering cats will bring some benefit or ward off some harm, then there is nothing wrong with it, as it says in al-Kubra.”

(al-Fawaakih al-Dawaani, 2/346)

Hence we say that if there is some benefit in neutering the cat and if that will not cause its death, then it is permissible.

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said:

If there are too many cats and they are a nuisance, and if the operation will not harm them, then there is nothing wrong with it, because this is better than killing them after they have been created. But if the cats are ordinary cats and are not causing a nuisance, perhaps it is better to leave them alone to reproduce.

Fataawa Islamiyyah, 4/448

And Allaah knows best.

what I believe is, its all depends on the owner and their intention. Do what's best to all.