In the Krita age the perforinance of sacrifices was not required. Such performance became necessary in the Treta age. In the Dvapara, sacrifices have begun to fall off. In the Kali, the same is the case with them,
त्रेतायुगे विधिस्त्वेष यज्ञानां न कृते युगे। द्वापरे विप्लवं यान्ति यज्ञाः कलियुगे तथा॥