I have some left over Purina Start and Grow (medicated) feed from when my hens were chicks, it has been kept in my house, and sealed up. My hens are around 9 months old now, and are eating regular chicken feed. I wanted to know if I could mix this left over Start and Grow with their regular feed. Would it do them any harm? I hate to waste this left over feed! But I will if it would do them any harm. Anyone have any info on this?