Of all kinds of animal killing, the killing of cows is most vicious because the cow gives us all kinds of pleasure by supplying milk.
(Bhagavad-Gita----14:6----purport).

In modern human society, spiritual knowledge is neglected, and cow killing is encouraged. It is to be understood, then, that human society is advancing in the wrong direction and is clearing the path to its own condemnation.
(Bhagavad-Gita----14:16----purport).

Why should men kill cows for their selfish purposes? Why should man not be satisfied with grains, fruits and milk, which, combined together, can produce hundreds and thousands of palatable dishes.
(Srimad Bhagavatam----1:10:4----purport).

Unfortunately, in modern civilization, men are busy killing the cows that are the source of yogurt, milk and ghee, they are cutting down all the trees that supply honey, and they are opening factories to manufacture nuts, bolts, automobiles and wine instead of engaging in agriculture.
(Srimad Bhagavatam----5:16:25----purport).

According to Vedic culture, destroying the undeveloped embryo of the soul in the womb is as sinful as killing a cow or a brāhmaṇa. In the embryo, the living entity is present in an undeveloped stage. The modern scientific theory that life is a combination of chemicals is nonsense; scientists cannot manufacture living beings, even like those born from eggs. The idea that scientists can develop a chemical situation resembling that of an egg and bring life from it is nonsensical. Their theory that a chemical combination can have life may be accepted, but these rascals cannot create such a combination. This verse refers to bhrūṇasya vadham—the killing of a bhrūṇa or destruction of the embryo.
(Srimad Bhagavatam----9:9:31----purport).

According to Vedic principles, a brāhmaṇa, an old man, a woman, a child or a cow cannot be killed under any circumstances.
(Srimad Bhagavatam----10:1:37----purport).

At the present moment, the killing of cows and the killing of children is going on unrestrictedly, and therefore this civilization is not at all human, and those who are conducting this condemned civilization are uncivilized asuras.
(Srimad Bhagavatam----10:3:22----purport).

Killing the cows and spoiling the land will not solve the problem of food.
(Srimad Bhagavatam----10:7:13-15----purport).

Especially in this age, Kali-yuga, cows are being killed all over the world, and as soon as there is a movement to establish brahminical civilization, people in general rebel.
(Srimad Bhagavatam----10:4:41----purport).

"Cow-killers are condemned to rot in hellish life for as many thousands of years as there are hairs on the body of the cow."
(Sri Caitanya Caritamrta----1:17:166----translation).

Slaughtering poor animals is also due to the mode of ignorance. The animal killers do not know that in the future the animal will have a body suitable to kill them.
(Bhagavad-Gita----14:16----purport).

Animal slaughter is one of the four major vices of Kali-yuga.
(Srimad Bhagavatam----1:1:6----purport).

The material world is itself a place always full of anxieties, and by encouraging animal slaughter the whole atmosphere becomes polluted more and more by war, pestilence, famine and many other unwanted calamities.
(Srimad Bhagavatam----1:7:37----purport).

The spiritual regulative principles do not allow a man to slaughter weaker animals on one side and teach others peaceful coexistence.
(Srimad Bhagavatam----1:13:47----purport).

Men do not understand that because they unrestrictedly kill so many animals, they also must be slaughtered like animals in big wars.
(Srimad Bhagavatam----4:26:5----purport).

The devotees are pained to see the hunting and killing of animals in the forest, the wholesale slaughter of animals in the slaughterhouses, and the exploitation of young girls in brothels that function under different names as clubs and societies.
(Srimad Bhagavatam----4:26:9----purport).

At the present day, however, not only are animals killed in the name of sacrifice, but the killing of animals has increased enormously because of the increasing number of slaughterhouses. Slaughtering animals, either for religion or for food, is most abominable and is condemned herein.
(Srimad Bhagavatam----7:15:10----purport).

In Kali-yuga, instead of drinking milk, people prefer to slaughter an animal and eat its flesh.
(Srimad Bhagavatam----8:6:12----purport).

Materialistic householders cruelly slaughter animals such as goats without any understanding of the dark consequences of their activities.
(Srimad Bhagavatam----11:5:8----purport).

The slaughterer of the animal is suitably punished by the material energy, just as a murderer is punished by the government through police action.
(Mukunda-Mala-Stotra).