The Messenger of Allah ﷺ forbade sacrificing an animal that had lost most of its horn or ear, Qatadah said: I mentioned that to Saʿeed bin Al-Musayyab and he said: Yes, the one that has lost half or more of that.
أَنَّهُ سَمِعَ عَلِيًّا يَقُولُ نَهَى رَسُولُ اللهِ ﷺ أَنْ يُضَحَّى بِأَعْضَبِ الْقَرْنِ وَالْأُذُنِ قَالَ قَتَادَةُ فَذَكَرْتُ ذَلِكَ لِسَعِيدِ بْنِ الْمُسَيِّبِ فَقَالَ نَعَمْ الْعَضَبُ النِّصْفُ أَوْ أَكْثَرُ مِنْ ذَلِكَ