Cow dung dried and used to cook on.
It is known that a living cow is more worth then slaughtering it young. A life time milk and cow dung to build huts to avoid insects and also to cook on.
Madurai counts a lot of formal farmers living here now. They brought their habits with them and you still see a lot of cows running around in town and ladies gathering the cow dung.
Nothing get lost in India, simple people still have to struggle for life.