The animal for Ritual Slaughter should be flawless
The Most Beloved Prophet (May Peace and blessing of ALLAH be upon him) has stated: We should check ear and eyes of animals carefully and should neither select the one for ritual slaughter that has severed front side of ear nor the one that has severed back side of ear or bearing hole in the ear.
(Sunan Tirmidhi, vol. 3, pp. 165, Hadis 1503)