Anyone can live only on milk. If you have got the opportunity to drink one pound milk maximum, not very much — half-pound is sufficient; suppose one pound — then you don't require any other foodstuff. Only this cow's milk will help you, it is so nice. And it gives very nice brain, not pig's brain. So it is so important thing. Other…, why Krsna says go-raksya? He did not say that "pig-raksya." No. "Dog-raksya," no. Now they are interested in dog-raksya instead of cow-raksya. This is the civilization. They'll spend millions of dollars for dog, not for cow.

From Srila Prabhupada's lecture on Srimad-Bhagavatam 6.1.21 — May 21, 1976, Honolulu