Chicks born with 2 vents can be a common birth defect. Many have reported here on older threads that both vents work, and the chickens have grown into adults. It doesn’t hurt to treat with Corid if she has been having intestinal shed or blood for a week. It is a safe medicine.
Here is a thread where many reported chicks with 2 vents that had laid eggs:
https://www.backyardchickens.com/threads/hen-with-2-vents-graphic-pic-update.30245/page-5
Here is a thread where many reported chicks with 2 vents that had laid eggs:
https://www.backyardchickens.com/threads/hen-with-2-vents-graphic-pic-update.30245/page-5