Members of the protein family having similarity to BPI (bactericidal/permeability increasing protein) (the BPI-like proteins), also known as the PLUNC (palate, lung and nasal epithelium clone) family, have been found in a range of mammals; however, those in species other than human or mouse have been relatively little characterized. Analysis of the BPI-like proteins in cattle presents unique opportunities to investigate the function of these proteins, as well as address their evolution and contribution to the distinct physiology of ruminants. The present review summarizes the current understanding of the nature of the BPI-like locus in cattle, including the duplications giving rise to the multiple BSP30 (bovine salivary protein 30 kDa) genes from an ancestral gene in common with the single PSP (parotid secretory protein) gene found in monogastric species. Current knowledge of the expression of the BPI-like proteins in cattle is also presented, including their pattern of expression among tissues, which illustrate their independent regulation at sites of high pathogen exposure, and the abundance of the BSP30 proteins in saliva and salivary tissues. Finally, investigations of the function of the BSP30 proteins are presented, including their antimicrobial, lipopolysaccharide-binding and bacterial aggregation activities. These results are discussed in relation to hypotheses regarding the physiological role of the BPI-like proteins in cattle, including the role they may play in host defence and the unique aspects of digestion in ruminants.