Small yield of RNA after on column DNAs digestion , Why - (Feb/21/2014 )

Dear All, 

I extracted RNA from duck tissue and it was really high quantity 2000 ng/µl  by nanodrop. After that I repeated the extraction with on coulmn DNAse digestion and the quantity dramatically dropped down to 120 ng/µl 

What is cause, is the Nanodrop measure the RNA and the DNA together ? 

Yes, it fails to distinguish them (except for the difference in A280/A260 which is minor, and can't be trusted). You may have introduced RNAses in your DNAse treatment.

May be, but if we assume a nice condition, is this is normal that your RNA quantity reduced after DNAse digestion?

No. But you can lose RNA in the cleanup afterwards.