A filter bonnet (200) for an open-top cage (3) includes a filter top (220) adapted to cover the open top of the open-top cage (3). The filter top (220) has a body portion with a perforated top wall (222, 224) and side walls (230) extending therefrom forming an open bottom end. A shield (250) is permanently affixed to the top wall (222, 224) and disposed within an area defined by the side walls (230).
