You have seen the picture, Krsna, Vrndavana picture, Krsna's father transferring Krsna — they were going on bullock carts, no motorcar. You have seen the picture. So formerly, transport was bullock carts. The cows and the bulls, the bulls were employed for agricultural purpose, for drawing the carts. So there was no necessity of motorcar. Now you have got motorcar, motor-tractor, you don't want the bullocks; therefore kill them. How you can utilize them? Therefore you must have slaughterhouse to kill them. And as soon as you kill them, then you have to eat them.
From Srila Prabhupada's lecture on Srimad-Bhagavatam 7.5.22–32 — May 27, 1972, Los Angeles