Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.111.

A sacrificial animal should satisfy the following conditions:

1. It should be two years old, if it is an animal other than a sheep. As for sheep, even a six month old lamb may be sacrificed, but it should be fat and healthy. As for a camel, it must be at least five years old, a cow two years old, and a goat a year old at least.

2. It should be healthy and free from all physical defects. It should not be one eyed, nor should it limp, be mangy, or very thin and weak. Al-Hasan said that the scholars said: “If a man purchases a healthy animal for sacrifice. but later before its slaughtering it becomes sick or loses one eye or develops a limp in her legs, then such a person may slaughter it as a sacrifice and that will suffice him (to fulfil his obligation).” This was reported by Sa’id bin Mansur.