a. Why are cows sacred?

The cow was the first animal that the Hindus domesticated. In the Vedic age the cow was a blessing to the rural community.
The cow is a maternal figure [Gau mata or mother cow], a caretaker of her people, also seen as a divine bounty of the earth. Lord Krishna was raised as a cowherd, and played His flute with the rest of his friendly cowherd mates. He is a friend and a protector of the cows, often called “Gopala”.
The cow is considered a sacred animal as it provides us with life-sustaining milk. It is considered an auspicious act to feed the cows first before eating once’s food.
Ayurveda promotes the Sattvic qualities of milk, and dairy products, so most Hindu families drink milk and eat milk based products to provide the essential proteins and nutrients. In the rural communities, bulls are used for ploughing the fields and transportation. Cow dung is used as a fuel, and can generate heat. Village homes are plastered with a mixture of cow dung/mud mixture, providing insulation. Cow dung is rich in minerals and is an excellent fertilizer. Rituals involving cow dung and ghee [clarified butter] for sacred fires are considered to purify the atmosphere, are antipollutant and anti-radiation. Some of the Hindu rituals use a combination of milk, yogurt, ghee, honey and sugar as offerings for prayer services.
It is hardly surprising that the cow occupied the position as a mother in the life of a child. It is considered a sin to kill a cow and eat beef. The vedic scriptures emphasize that the cow must be protected and cared for.

Other reading material: Read Why Hindus don’t eat beef? (22a), https://voiceofhindus.org/why-cows-are-sacred-for-hindus-and-why-they-dont-eat-beef/
Relevant videos:

Contributor: Dr. Jyoti Lulla