A childhood question that would be haunting in the mind of every Hindu across the world “ Why do we Indians burn cow dung during Yagya”? So, today your childhood question will be answered.
So, we will start by knowing the significance of HOLY COW in Hinduism.
The cow is only an ideal animal in Deity Bramha’s creation and as per spiritual science, the four Purushārthas, namely, Dharma, Artha, Kāma, and Moksha can be acquired by serving the cow. While praising the cow, the principal Deities, namely, Bramha, Vishṇu, and Shiva have narrated a shloka which means
“O Destroyer of sins! You are the mother of all Deities. You are the reason for Yagya (sacrificial fire). Among all Tirthas (Holy places), you are the holiest. I pay my obeisance to you.”

The cow is not a mere animal for Hindus. They consider Cow as the adobe of 33 crore Hindu Deities and hence Cow is considered as sacred in Hindu Dharma. A cow has been treated as auspicious and also a symbol of compassion and piousness. Even Vedas also mentioned the cow saying that she is the mother, sister, and daughter, and one should always respect her with purity.
Hindu religion considers that every element of the cow is sacred majorly cow milk, cow urine, and cow dung which was later backed by science that there are many health benefits of consuming cow milk which no other cattle milk can provide and there are many medicinal benefits of consuming pure cow urine has healing power but you will be surprised by knowing as per Hindu religion belief Goddess Lakshmi resides in the dung of the cow and they also believe that saluting cow and cow dung one can gain all the wealth and Dharmas and cow dung is also one of the PANCHAGAVYA ( 5 products of the cow) and are majorly used for Yagya/Agnihotri ( fire sacrifices). Cow dung along with the other Panchagavya ghee, milk, curd, and urine are used for the Yagya that gives positive energy in the environment majorly the deadly combination of dung and ghee which detoxify the atmosphere.
Many people believe that Hindu rituals somewhat go hand in hand with science, so do I. You will again be amazed by the fact that the deadly combination of dry dung and ghee while burning produces oxygen unlike any other combustion material that produces CO2 with many toxic substrates but not oxygen, and I believe that with the great power of meditation, yagya, and knowledge the Hindu Saint knew that the problems from deforestation might create several disaster and wildlife will lose their home, so Panchagavya will not only lead to the purification of atmosphere but will also help in producing more oxygen from where dung of the cow became HOLY COW DUNG for Hindus. One can easily notice the use of cow dung during several festivals of India like Bhogi, Holika, Sankranti, Lohri, Pongal, and Bishu.

It is also used during the festivals of Naagpanchami, Nuakhai, Onam, Gudi-Padwa, and Govardhan pooja festivals to invite the auspicious energies of Goddess Lakshmi into one`s life. Cow dungs are often used during the last rite of a Hindu person.