Sheikh Muhammad al-Fawzân
It is permissible to eat animals that may have been mistreated as long as they were properly slaughtered. The lawfulness of the meat is not conditional upon how the animal was treated before being slaughtered.
It is important to note that it is impermissible in Islam to mistreat animals. It is in fact a very serious sin that can be the reason for serious punishment in the Hereafter. It is also the duty of the governments of Muslim countries to ensure that this mistreatment does not take place. However, the lawfulness of the meat is unaffected. The sin in this case is solely upon the one who carries out the mistreatment.
If it is known that a certain slaughterhouse mistreats their animals, it might be a good idea to refrain from patronizing them to discourage their mistreatment.
And Allah knows best.
Source: Islam Today