Is it permissible to kill diseased or defective chicks by striking them forcefully on the back? And is there any doubt concerning the lawfulness of the money if this act is forbidden? And is the questioner sinful if he remains silent about his colleagues?

If it is not feasible to treat sick birds, or if their treatment involves hardship, and they cannot be utilized, then it is permissible to kill them to relieve them of their suffering, and it may even be recommendable. This is based on what Al-Mawwaq reported from Ibn al-Qasim, who stated the permissibility of slaughtering a sick animal from which no benefit is expected, and what Ibn Rushd said about this being a form of relief for the animal. It has also been narrated from the Nawazil al-Barzali that it is permissible to kill young kittens if their mothers' food supply is scarce. Kindness should be observed in the method of killing them. However, if there is a justification for their survival or treatment, it is not permissible to kill them. If someone else undertakes to kill them, then advise them and enjoin them to have mercy on them. The salary of the questioner from working in poultry farms is permissible.