This invention relates to a method for selectively isolating IgY(.DELTA.Fc)
avian antibodies from IgY avian antibodies. For example, the method
includes: (a) providing an aqueous fraction from yolk of an egg of an
anseriform bird; (b) precipitation IgY antibodies using a first
precipitant salt; and (c) precipitating the IgY(.DELTA.Fc) antibodies from
a supernatant using a second precipitant salt to provide an isolated
preparation enriched for IgY(.DELTA.Fc) antibodies.