In Bhagavad-gita Lord Krsna advises go-raksya, the protection of cows. This is essential because if cows are cared for properly they will surely supply sufficient milk. We have practical experience in America that in our various ISKCON farms we are giving proper protection to the cows and receiving more than enough milk. In other farms the cows do not deliver as much milk as in our farms; because our cows know very well that we are not going to kill them, they are happy, and they give ample milk. Therefore this instruction given by Lord Krsna—go-raksya—is extremely meaningful. The whole world must learn from Krsna how to live happily without scarcity simply by producing food grains (annad bhavanti bhutani [Bg. 3.14]) and giving protection to the cows (go-raksya). Krsi-go-raksya-vanijyam vaisya-karma svabhavajam [Bg. 18.44].

From Srila Prabhupada's purport to Srimad-Bhagavatam 9.15.25