In one embodiment, the present invention relates to novel bovine adenovirus expression vector systems which utilize the following regions of the bovine adenovirus genome: nucleotides 4,092-5,234； nucleotides 5,892-17,735； nucleotides 21,198-26033 and nucleotides 31,133-34,445. These regions can be used, among other things, for insertion of foreign sequences, for provision of DNA control sequences including transcriptional and translational regulatory sequences, or for diagnostic purposes to detect the presence of viral nucleic acids or proteins encoded by these regions, in a subject or biological sample. In another embodiment, the present invention relates to novel methods for the construction, isolation and propagation of recombinant bovine adenovirus (BAV) with deletions (and optionally insertions of heterologous sequence) in the E3 region. Recombinant BAV containing insertions of genes encoding protective determinants of a pathogen stimulate enhanced systemic and mucosal immune responses and protect host animals against challenge by the pathogen.
