[Histonet] Normal Goat Serum for IHC

[Misono, Kaori]

Dear Histonetter,

I am a reserach technician in the lab.
I use Normal Goat Serum (NGS) for immunofluorescent IHC stainig as a blocking (10%). Recently I got a new batch of NGS and used it. Even my reliable primary antibody was negative on the rat brain tissue. I tested old vs new NGS, and old one worked. 
Does this happen a lot?
Could someone know about good NGS supplier for the staining? 
Thank you for your help.

Kaori