Guest: We can take care of cows, can't we?
Prabhupāda: You should. Otherwise you are ungrateful. You are drinking milk, you are taking so much butter, milk product, and as gratitude you are killing cows? You should be ashamed. Even if you have no human feelings. You suck the breast of your mother and kill? Is that humanity?
So this will be, in due course, the milk supply will be stopped. That is stated in the Śrīmad-Bhāgavatam. There will be no more milk supply at the end of this Kali-yuga. Three, four things will be stopped—grains, sugar, and milk will be stopped. And fruits will not be... Without any pulp. It will be simply seed. Just like in mango there is seed and pulp. In future you'll simply have seed, no pulp. So you'll eat mango simply by tasting the seed. There will be no more mango pulp. These are stated in the Bhāgavatam.
So people are so foolish that they are continually committing sinful activities. Therefore yajña is recommended. But they cannot perform yajña also. The only alternative is to take to Kṛṣṇa consciousness to save you from all risky life.