The invention provides a transgenic animal having within its genome a
transgene construct for gastrointestinal tract specific expression of a
protein. In a preferred embodiment, the protein is a phytase or a
homologue thereof. Such proteins may be heterologous and may be
specifically expressed in the salivary gland of the animal by operably
linking the nucleic acid sequence encoding the protein with regulatory
sequence including a salivary gland protein promoter/enhancer. Also
provided are methods of expressing and producing proteins using such
nucleic acid constructs. Further, antibodies specific to such proteins
and immunological diagnostic kits are also provided.