You mean your primary ab is raised in goat? try with blocking with fish gelatin, that would help. 

Yes, my primary ab is raised in goat. So I cannot use either BSA or milk, which could well be contaminated with bovine IgG. Thank you for your answer. I have read information about using donkey serum, or something like that, did you try these things yourself? 

gelatin will be OK

Horse serum may work. Or change secondary antibody supplier.

Sorry, if I am mistaken but unless there is something I don't know about cross reactivity between goat and bovine (= cow) antibodies, you should be able to use BSA or milk (as long as it is not goat milk) as a blocking agent.  Please correct me if I'm wrong.

I also wondered why rabbit-anti-goat antibody cross reacts with cow milk. Maybe there is some contamination in various forms? Anyway, blocking the membrane with milk doesn't work in my case. I'm trying to use BSA and without blocking after drying the membrane.

Also another problem could be the type of membrane...sometimes I've found that a primary Ab that does not work on nitro, work on PVDF..and viceversa...also try that..

Mai Sun - Did you find a resolution to this?

@Swati Khare I'm trying to use protein free blocking solution