The Rishis said The Veda declares that in sacrifices the offerings should consist of seeds. Seeds are called Ajas. You should not kill goats.
ऋषय ऊचुः बीजैर्यज्ञेषु यष्टव्यमिति वै वैदिकी श्रुतिः। अजसंज्ञानि बीजानि च्छागं नो हन्तुमर्हथ॥