Mastitis Resistance to Enhance Dairy Food Safety

NON-TECHNICAL SUMMARY: Mastitis susceptible and resistant dairy cows will be used to identify potential genes, immune components, and other factors associated with and responsible for mastitis resistance. Virulence factors that allow mastitis pathogens to invade the udder, multiply there and produce harmful substances that result in inflammation, reduced milk production and altered milk quality will be determined.
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APPROACH: Mastitis susceptible and resistant dairy cows will be identified in a dairy herd that has an extensive microbiological database. Clones will be derived from ovarian cells obtained from susceptible and resistant dairy cows and will be used to determine potential genes, immune components, and other factors associated with and responsible for mastitis resistance. Expression of candidate gene (interleukin-8 receptor) haplotypes will be delineated for mastitis susceptible and resistant dairy cows and compared with their mastitis history. Functional differences in phagocytic function and gene expression of mastitis resistant and susceptible cows will be evaluated. Potential streptococcal virulence factors will be identified and characterized. Work will continue on mastitis pathogen virulence components affecting adherence to and invasion of mammary epithelial cells, and on prevention and control of mastitis in heifers near calving. Identification of foodborne pathogen reservoirs on dairy farms will be determined. Known and novel adipocyte derived factors will be evaluated for their impact on monocyte/macrophage cell function during the periparturient period in comparison to later stages of lactation.
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PROGRESS: 2002/10 TO 2007/09<BR>
OUTPUTS: Identification of host mechanisms associated with disease susceptibility and resistance have focused on identifying genetic markers for disease, the functional ability of neutrophils (the first responders to infection) in cattle more susceptible to mastitis, and immune-related proteins produced by mammary epithelial cells. A series of markers in two immune-related genes (CXCR1 and NRAMP) were associated with mastitis susceptibility in Holstein dairy cows. Additional studies into the mechanism for greater susceptibility in cows with the CXCR1 marker have indicated the ability of neutrophils to migrate and survive is disrupted at the cellular level. Mammary epithelial cells also were discovered to produce beta-defensin, an antimicrobial peptide capable of killing major mastitis pathogens such as Escherichia coli and Streptococcus uberis. The ability of mastitis pathogens to cause disease depends upon their ability to evade host defenses. An important step forward in identifying mechanisms S. uberis interacts and evades host responses was development of a S. uberis in vivo challenge model. This model has been used to delineate immune responses to infection and evaluate potential vaccine antigens, protocols, and antibiotic therapies. More basic research has centered on the ability of certain strains of E. coli and S. uberis to adhere to and invade mammary epithelial cells. By invading mammary epithelial cells, bacteria can avoid the host response and cause chronic infections. Other studies focused on developing PCR -based methods for detecting major mastitis and food safety-related pathogens in milk, virulence genes, and antibiotic resistance genes. These methods were used to assess milk quality for the presence of bacteria such as E. coli, Staphylococcus aureus, S. uberis, Campylobacter jejuni, and Salmonella species. This knowledge not only provides information relative to quality of the milk supply, but may be developed into methods for rapid detection. When a cow develops infection, antibiotics are used to help the animal eliminate the bacteria. However, with the ability of some bacteria to invade epithelial cells, bacteria not only hide from host defenses, but also antibiotic therapy. Because of this, an in vitro model was established to assess antibiotic efficacy in killing bacteria that have invaded mammary epithelial cells. Several of the more applied projects evaluated antibiotic therapy protocols. For example, one study focused on the use of extended therapy with two, five, or eight days of pirlimycin therapy following experimental challenge with S. uberis. A separate study evaluated use of extended therapy of subclinical infections with ceftiofur. In each study extended (8 day) therapy was significantly more effective at eliminating infections than 2 days. This information can be used to identify sires and cows with greater mastitis resistance and produce healthier offspring. <BR>PARTICIPANTS: Research associates/Technical support - Raul Almeida, Rose Clift, Barbara Gillespie, Susan Headrick, Mark Lewis, Doug Luther, Shelton Murinda, Hyang-mi Nam, Lien Nguyen, Dilip Patel, Maria Prado, Ashish Sawant, Velusamy Srinivasan. Graduate students - Ali Elliot, PhD candidate; Sarah Piper; Magdelana Rambeaud, PhD; Angela Pollock, MS; Sara Youngerman, MS. <BR>TARGET AUDIENCES: The primary target audiences are veterinarians and producers. These audiences are reached through participation in the annual NMC (formerly National Mastitis Council) meeting held each year. The objective of this meeting is designed to transfer new knowledge and technology to veterinarians, producers, and other businesses associated with the dairy industry. Other means of contact have included publication in scientific journals, extension-related activities, guest speaking engagements at relevant meetings/workshops, and articles in lay journals.
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IMPACT: 2002/10 TO 2007/09<BR>
The knowledge gained from these studies will aid breeding decisions to select for healthier animals, help develop rapid mastitis detection methods, and generate novel preventive and therapeutic strategies to control mastitis. As a result, dairy cows will be healthier, more productive, and provide higher quality milk. Higher milk quality will promote new export markets help improve dairy producer sustainability. Additionally, with public concerns over animal welfare and antibiotic resistance, this research provides solutions to improve animal health while minimizing the use of antibiotics.