Serine protease inhibitor involved in antimicrobial egg defense preventing contamination of table eggs (non-fertilized eggs) and protecting the chick embryo (fertilized eggs) (Probable). Inhibits trypsin, chymotrypsin, elastase, subtilisin and a proteinase of fungus Aspergillus oryzae (PubMed:13944692, PubMed:6904299, PubMed:6838526, PubMed:14519973, PubMed:14609095, PubMed:22010862). Inhibits calcium-activated potassium channels KCNMA1 (bovine) and slo (Drosophila) (PubMed:8973172). Has antibacterial activity against B.thuringiensis LMSA 3.06.004, but not against S.aureus CIP 103 811, P.aeruginosa PAO1, B.cereus ATCC6464 or B.subtilis ATCC 6633 (PubMed:22010862). Expressed in oviduct (at protein level) (PubMed:3571241). Expressed in egg white (at protein level) (PubMed:6838526, PubMed:14519973, PubMed:23122126, PubMed:25436390). Expressed in egg yolk plasma of non-fertilized eggs (at protein level) (PubMed:22010862). Expressed in the magnum of the oviduct (at protein level) (PubMed:25436390). Expressed in oviduct (PubMed:3571241, PubMed:14609095). Expressed in liver (PubMed:3571241, PubMed:11572089, PubMed:22010862). Expressed in the cortico-medullary border region of the bursa of Fabricius by the bursal secretory dendritic-like cells (PubMed:15252730). Highly expressed in the magnum of the oviduct, and at a lower level in uterus. Weakly expressed in white isthmus and very weakly in infundibulum. Not expressed in duodenum and kidney (PubMed:22010862). Expressed in liver of pre-laying and egg-laying hens throughout sexual maturation. Expression increases gradually from 13 weeks of age reaching its maximum at 15 weeks of age (pre-laying hens). A significant decrease in expression is observed in 41-week-old hens (egg-laying), a level that is significantly lower than that measured initially in 13-week-old pullets. Expression is regulated by dietary stress. Significantly increased expression between days 0 to 5 in egg whites of eggs laid by corticosterone-fed hens (at protein level). Decreased expression at day 14 in the magnum of the oviduct in the corticosterone-fed laying hens (PubMed:25436390). Significantly increased expression by estrogen. Rapidly up-regulated within 0.5 hour after extrogen exposure with a peak at 1-4 hours and diminishing thereafter (PubMed:11572089). Up-regulated during sexual maturation of pullets (PubMed:22010862). Seems to have at least five separate non-overlapping active inhibitory domains; two for trypsin, two for chymotrypsin and one for elastase. They can be bound to the domains simultaneously. Glycosylated. Causes an allergic reaction in humans. Binds to IgE of egg-allergic patients. Immunoreactivity is lost by simulated gastric and gastroduodenal digestion (PubMed:23122126). Binds to rabbit anti-ovomucoid IgG antibody indicating the cross-reactivity between this protein and the ovomucoid protein from egg white (PubMed:6838526). The galactomannan conjugate of this protein prepared through the Maillard reaction shows almost the same inhibitory activity toward trypsin, chymotrypsin and elastase, with stronger heat and emulsion stability, and better emulsifying properties than the untreated protein. The conjugate can therefore be useful for industrial application. Prevents symptomatic gastoroenteritis in vivo in a mouse model of rotavirus infection. Significantly inhibits intestinal replication of EDIM strain of murine rotavirus in infant mice up to 4 days after intragastrical administration of the virus. Extended N-terminus.