A filter top assembly (20) for a cage, wherein the assembly (20) includes a bonnet (100) having a perforated top wall to protect filter paper (200) placed above the top wall. The perforations (120) may be small enough to prevent an animal from getting a purchase position and spaced apart sufficiently to prevent the animal from biting the spacing between the perforations (120). The bonnet (100) may also include one or more elevated ribs (142,144) to retain the filter paper (200) suspended above the bonnet.
