Catalog and custom-produced Polyclonal Antibodies can be provided in different formats, such as: 

Serum (1)
Contains a mixture of various immunoglobulins against different antigens (met by an animal during immunization course). The concentration of specific antibody in serum can be low, and usually varies between 0.5 to 5 % of the total IgG pool (concentration of IgG varies from 10 to 20 mg/ml between immunized animals). 
Information presented on the  antibody product information sheet: 
50, 100 or 200 µl serum

Affinity purified using Protein A or G (2)
This procedure will yield a total immunoglobulin fraction. Antibodies specific to a given target will vary from 0.5 to 5 % of such total IgG pool. 
Information presented on the  antibody product information sheet: 
100 or 200 µg

Affinity purified using specific antigen (protein, peptide) (3) 
This procedure is done using a matix, coupled with a specific protein or peptide used to elicit the given antibody. This will result in a specific antibody of >80 % purity, depending on the procedure.  
Information presented on the antibody product information sheet: 
50, 100 or 200 µg

A product which is provided as 50 µl of serum (1), or 50 µg of serum purified on Protein A or G (2), will not contain the same amount of specific antibody as 50 µg of antibody purified using the specific antigen (3). 

 

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50 µg of antibody purified by affinity chromatography on Protein A or G will contain less specific antibodies than 50 µg of antibodies purified using matrix coupled with antigen (protein or peptide). 

For any type of conjugation with HRP, ALP or fluorophore, the antibody needs to be affinity purified on the specific antigen (used to produce it) to a specific immunoglobulin fraction.