When the government neglects agriculture, which is necessary for the production of food, the land becomes covered with unnecessary trees. Of course, many trees are useful because they produce fruits and flowers, but many other trees are unnecessary. They could be used as fuel and the land cleared and used for agriculture. When the government is negligent, less grain is produced. As stated in Bhagavad-gītā (18.44), kṛṣi-go-rakṣya-vāṇijyaṁ vaiśya-karma svabhāva jam: the proper engagements for vaiśyas, according to their nature, are to farm and to protect cows. The duty of the government and the kṣatriyas is to see that the members of the third class, the vaiśyas, who are neither brāhmaṇas nor kṣatriyas, are thus properly engaged. Kṣatriyas are meant to protect human beings, whereas vaiśyas are meant to protect useful animals, especially cows.
(Srimad Bhagavatam----6:4:4----purport).

By nature's law, or the arrangement of the Supreme Personality of Godhead, one kind of living entity is eatable by other living entities. As mentioned herein, dvi-padāṁ ca catuṣ-padaḥ: the four-legged animals (catuṣ-padaḥ), as well as food grains, are eatables for human beings (dvi-padām). These four-legged animals are those such as deer and goats, not cows, which are meant to be protected. Generally the men of the higher classes of society—the brāhmaṇas, kṣatriyas and vaiśyas—do not eat meat. Sometimes kṣatriyas go to the forest to kill animals like deer because they have to learn the art of killing, and sometimes they eat the animals also. Śūdras, too, eat animals such as goats. Cows, however, are never meant to be killed or eaten by human beings. In every śāstra, cow killing is vehemently condemned. Indeed, one who kills a cow must suffer for as many years as there are hairs on the body of a cow. Manu-saṁhitā says, pravṛttir eṣā bhūtānāṁ nivṛttis tu mahā-phalā: we have many tendencies in this material world, but in human life one is meant to learn how to curb those tendencies. Those who desire to eat meat may satisfy the demands of their tongues by eating lower animals, but they should never kill cows, who are actually accepted as the mothers of human society because they supply milk. The śāstra especially recommends, kṛṣi-go-rakṣya: the vaiśya section of humanity should arrange for the food of the entire society through agricultural activities and should give full protection to the cows, which are the most useful animals because they supply milk to human society.
(Srimad Bhagavatam----6:4:9----purport).

As for the maintenance of his family, a gṛhastha, while earning what he requires for his living, must be very conscientious and must not undergo extraordinary endeavor simply to accumulate money and unnecessarily increase in material comforts. Although a gṛhastha should externally be very active in earning his livelihood, he should internally be situated as a fully self-realized person, without attachment for material gains. His dealings with family members or friends should be performed simply to fulfill their purpose; one should not be extravagantly engaged in this way. Instructions from family members and society should be accepted superficially, but in essence the gṛhastha should be engaged in occupational duties advised by the spiritual master and śāstra. Specifically a gṛhastha should engage in agricultural activities to earn money. As stated in Bhagavad-gītā (18.44), kṛṣi-go-rakṣya-vāṇijyam-agriculture, cow protection and trade-are special duties of gṛhasthas. If by chance or by the grace of the Lord more money comes, it should be properly engaged for the Kṛṣṇa consciousness movement. One should not be eager to earn more money simply for sensual pleasure. A gṛhastha should always remember that one who is endeavoring to accumulate more money than necessary is to be considered a thief and is punishable by the laws of nature.
(Srimad Bhagavatam----7:14--summary).

Milk is compared to nectar, which one can drink to become immortal. Of course, simply drinking milk will not make one immortal, but it can increase the duration of one's life. In modern civilization, men do not think milk to be important, and therefore they do not live very long. Although in this age men can live up to one hundred years, their duration of life is reduced because they do not drink large quantities of milk. This is a sign of Kali-yuga. In Kali-yuga, instead of drinking milk, people prefer to slaughter an animal and eat its flesh. The Supreme Personality of Godhead, in His instructions of Bhagavad-gītā, advises go-rakṣya, which means cow protection. The cow should be protected, milk should be drawn from the cows, and this milk should be prepared in various ways. One should take ample milk, and thus one can prolong one's life, develop his brain, execute devotional service, and ultimately attain the favor of the Supreme Personality of Godhead. As it is essential to get food grains and water by digging the earth, it is also essential to give protection to the cows and take nectarean milk from their milk bags.
(Srimad Bhagavatam----8:6:12----purport).

The surabhi cow is described as havirdhānī, the source of butter. Butter, when clarified by melting, produces ghee, or clarified butter, which is inevitably necessary for performing great ritualistic sacrifices. As stated in Bhagavad-gītā (18.5), yajña-dāna-tapaḥ-karma na tyājyaṁ kāryam eva tat: sacrifice, charity and austerity are essential to keep human society perfect in peace and prosperity. Yajña, the performance of sacrifice, is essential; to perform yajña, clarified butter is absolutely necessary; and to get clarified butter, milk is necessary. Milk is produced when there are sufficient cows. Therefore in Bhagavad-gītā (18.44), cow protection is recommended (kṛṣi-go-rakṣya-vāṇijyaṁ vaiśya-karma svabhāva jam).
(Srimad Bhagavatam----8:8:1----purport).

Pañca-gavya, the five products received from the cow, namely milk, yogurt, ghee, cow dung and cow urine, are required in all ritualistic ceremonies performed according to the Vedic directions. Cow urine and cow dung are uncontaminated, and since even the urine and dung of a cow are important, we can just imagine how important this animal is for human civilization. Therefore the Supreme Personality of Godhead, Kṛṣṇa, directly advocates go-rakṣya, the protection of cows. Civilized men who follow the system of varṇāśrama, especially those of the vaiśya class, who engage in agriculture and trade, must give protection to the cows. Unfortunately, because people in Kali-yuga are mandāḥ, all bad, and sumanda-matayaḥ, misled by false conceptions of life, they are killing cows in the thousands. Therefore they are unfortunate in spiritual consciousness, and nature disturbs them in so many ways, especially through incurable diseases like cancer and through frequent wars and among nations. As long as human society continues to allow cows to be regularly killed in slaughterhouses, there cannot be any question of peace and prosperity.
(Srimad Bhagavatam----8:8:11----purport).

The Supreme Personality of Godhead has instructed in Bhagavad-gītā (18.44), kṛṣi-go-rakṣya-vāṇijyaṁ vaiśya-karma-svabhāvajam: "Farming, cow protection and trade are the qualities of work for the vaiśyas." Nanda Mahārāja belonged to the vaiśya community, the agriculturalist community. How to protect the cows and how rich this community was are explained in these verses. We can hardly imagine that cows, bulls and calves could be cared for so nicely and decorated so well with cloths and valuable golden ornaments. How happy they were. As described elsewhere in the Bhāgavatam, during Mahārāja Yudhiṣṭhira's time the cows were so happy that they used to muddy the pasturing ground with milk. This is Indian civilization. Yet in the same place, India, Bhārata-varṣa, how much people are suffering by giving up the Vedic way of life and not understanding the teachings of Bhagavad-gītā.
(Srimad Bhagavatam----10:5:7----purport).

For human happiness, one must care for the animals, especially the cows. Vasudeva therefore inquired whether there was a good arrangement for the animals where Nanda Mahārāja lived. For the proper pursuit of human happiness, there must be arrangements for the protection of cows. This means that there must be forests and adequate pasturing grounds full of grass and water. If the animals are happy, there will be an ample supply of milk, from which human beings will benefit by deriving many milk products with which to live happily. As enjoined in Bhagavad-gītā (18.44), kṛṣi-go-rakṣya-vāṇijyaṁ vaiśya-karma-svabhāvajam. Without giving proper facilities to the animals, how can human society be happy? That people are raising cattle to send to the slaughterhouse is a great sin. By this demoniac enterprise, people are ruining their chance for a truly human life. Because they are not giving any importance to the instructions of Kṛṣṇa, the advancement of their so-called civilization resembles the crazy efforts of men in a lunatic asylum.
(Srimad Bhagavatam----10:5:26----purport).