Avidity maturation of an antibody represents an increasing affinity interaction between antibodies and antigens. However, this maturation is slowly induced in mammals [27] . We demonstrated that STAg-immunized hens produced large amounts of high avidity polyclonal IgY anti-STAg antibodies after the first booster, with early recognition of p30 proteins. It is known that SAG1 protein (p30) triggers the human IgG maturation in latter stages of T. gondii infection [28] . Additionally, IgY antibodies recognized a broad range of proteins, with distinct isoelectric points determined by 2D-immunoblot. Previous studies have shown that serum samples from naturally infected humans react to a broad spectrum of T. gondii proteins [29] and experimentally infected mice produce specific antibodies against high and low molecular weight antigens of tachyzoites [30] . Consistently, our results demonstrated that IgY anti-STAg presented an antigen recognition profile similar to mouse serum, although some antigens were more immunogenic for hens than mice, probably due to the phylogenetic distance among these animals. In addition, IgY antibodies raised against closely related parasites did not recognize STAg proteins, which denotes an interesting feature of the IgY system, since crossreactivity is a normal feature of mammalian IgG.