While the presence of lysine groups on an antibody is paramount, with regards to chicken IgY – it is too heavily glycosylated to work as well as bovine IgG with our kits. Although IgY will be labeled or modified with biotin to some extent, the sugars can interfere with binding to streptavidin in downstream applications. So the glycosylation can be an issue when working with IgY antibodies (in terms of downstream applications, where attachment to streptavidin is involved).