Feeding a cow is not considered a sin in Jainism if it is done with dayā, karuṇā, and ahimsā-bhāva.

A Jain may feed a cow when:

• the food is suitable and harmless for the cow,
• it does not involve violence to other जीवs,
• it is done without ego, show-off, or attachment,
• and it does not create unnecessary harm in the process.

In Jain ethics, the main concern is hiṃsā. So feeding an animal is generally seen as a good, compassionate act, not a sin.

However, if feeding is done in a way that causes harm, such as:

• giving food that is harmful to the cow,
• causing injury to other beings,
• or creating attachment and pride,

then that action can become spiritually unwholesome.

So the simple answer is: feeding a cow is usually पुण्य/meritorious, not sin, when done rightly.