Despite numerous advances in bovine infectious disease research, bovine respiratory disease (BRD) remains a significant disease threat and a cause of tremendous loss. Renewed efforts and innovative strategies are required to build on the successes of the past to achieve the successes of tomorrow. Continued and improved support of BRD research will prove to be a worthwhile investment. To achieve better coordination and more efficient use of resources, the following supportive actions should be considered. There should be coordination of integrative teams through an over-arching agency (United States Department of Agriculture (USDA)) to provide peer review and priority review for available public research funds. This would include use of development grants (as seed and matching funding) available to public/private partnerships. Testing and validation of new procedures in production settings (providing more than cost analyses) should be strengthened. Publication of studies should be promoted and old links between clinicians, diagnosticians and basic researchers should be re-established. Sets of ‘best practices’ should be published. Programs to support both basic and applied research through graduate fellowships, residencies, workshops and start-up funding for young research scientists should be strengthened. Sustained funding to train the next generation of research investigators should be addressed as a critical need.

The importance of host heterogeneity in generating aggregation was investigated using Heligmosomoides polygyrus (Nematoda) in laboratory mice. Parameters of infection were compared between inbred and outbred mice, between primary and challenge infection protocols, and between gavage and natural exposure protocols, to investigate the relative effects of innate resistance, acquired resistance and behaviour, respectively. Heterogeneity in acquired resistance was identified as the most consistent factor leading to variability and aggregation of H. polygyrus numbers in mice. This hypothesis was supported in two experiments where groups of mice did not develop resistance to challenge infection (use of certain inbred strains of mice and immunosuppression with corticosteroids in the drinking water) and where variability in worm numbers after the challenge infection was comparable with that after the primary infection. Heterogeneity in host behaviour, particularly in behaviours enhancing skin contact with larvae, also was associated with increased heterogeneity in worm burden, though not as consistently as heterogeneity in acquired resistance. Surprisingly, worm burdens were not more variable in outbred compared with inbred mice. Our data suggest that the relative contributions of innate resistance, acquired resistance and behaviour in generating variable worm burdens are likely to vary spatially and temporally.