Animal Sacrifice in Yajñas

Read this thread to know how animal sacrifice got started in Yajñas and what Rishis thought about it.

Once Upon a time, Great and Powerful Indra decided to do Yajña, there were large scale preparations, Rishis were chanting mantras, then Indra decided to SIay animals there

Rishis stopped him, Rishis clearly told him that There is NO mention of K!lling animals in Yajñas in shastras,

K!lling animals in Yajñas is against Dharma, hence please allow Brahmins to perform it according to shastras

Rishis said, Yajña must be done with seeds, this is what Dharma says.
But Imdra had a Big ego, he refused to follow Dharma

So they went to King Vasu and asked him, who is correct, King lied that you can do yajña with anything, because if this he was punished.

(Mahabharata AshwamedhikaParva adhyay 91)