وَإِنْ أَصَابَهُ عَيْبٌ كَبِيرٌ أَقَامَ غَيْرَهُ مَقَامَهُ، وَصَنَعَ بِالْمَعِيبِ مَا شَاءَ.
Translation: If it develops a serious defect, he substitutes another animal and may dispose of the defective one as he wishes.
‘Ayb kabīr is a significant, disqualifying defect.
In the obligatory-hady context, one does not treat a seriously defective animal as if the duty were fulfilled. The reading bi-l-ma‘īb means the defective animal; an online witness has a typographical variant.