I say, and with God's success: Al-'Atirah: It was the practice of a man that when a she-camel or a sheep gave birth, he would slaughter the first offspring it bore and eat and feed others from it. This has been abrogated by the sacrifice (Udhiyah). Abu Huraira - may God be pleased with him - reported that the Prophet - peace be upon him - said: "There is no Fr' (the first offspring), nor 'Atirah" in Sahih Muslim 3: 1564, and Sahih Bukhari 5: 2083. The Fr' is the first offspring that they used to slaughter. Refer to the explanation of Sahih Muslim by Al-Nawawi 1: 228, and God knows best.