I hate sick cows! Unfortunately, we all are faced with them from time to time. I prefer the proactive approach of preventing disease instead of trying to cure the disease. Traditionally, we have focused on proper nutrition and management practices to prevent disease. Another method that is gaining popularity is the use of genetics to select for healthier cows with naturally superior immune responses to minimize occurrence of disease. This type of approach has worked for rodents, poultry, and swine.
How do we evaluate the immune response?
The University of Guelph’s Ontario Veterinary College has developed a patented test to identify cows and calves with an enhanced immune responsiveness…also known as high immune responders (HIR). The test is based on the antibody-mediated and cell-mediated immune responses that determine the cow’s ability to fight off infections. The immune responses are measured by antibody production in response to an immunization protocol and delayed-type hypersensitivity assessed by skinfold thickness. The antibody-mediated immune response predominates in host defense against extracellular pathogens such as Escherichia coli. On the other hand, cell-mediated immune responses predominate against intracellular organisms like Mycobacterium avium subspecies paratuberculosis. Both responses are important to enhance in cows to provide a broad-based disease resistance to a multitude of pathogens.
A collaborative study between the University of Guelph and the Canadian Bovine Mastitis Research Network using 58 Holstein herds across Canada found that high, average, and low immune responders were found within each herd. Across all herds, approximately 15% of cows were high, 70% were average, and 15% were low immune responders.
Can we expect better health and performance with high immune responders?
Recently, studies are finding several benefits of HIR cows in a herd which include: 1) lower disease occurrence, 2) better response to vaccinations, and 3) more protective antibodies in colostrum.
A University of Guelph study conducted on a Florida Holstein herd found that cows identified as HIR had a decreased risk of developing mastitis, metritis, DA, and retained placenta. This suggests that breeding for enhanced immune responsiveness will decrease the incidence and severity of infectious and metabolic diseases. Based on the Guelph studies, it doesn’t appear that breeding for HIR would compromise milk yield or composition. However, cows with only a high antibody-mediated immune response had lower milk yield.
Approximately 75% of Canadian dairy producers surveyed acknowledged that identification of HIR cows and calves would be beneficial information for culling decisions, grouping, breeding, and treating animals. The dairy support industries representatives that were surveyed cited benefits that included targeting drugs or vaccines to specific groups (low vs. high) of immune responders, improving genetics, and increasing business opportunities with producers.
Can we really breed for immunity?
Fortunately, the antibody-mediated and cell-mediated immune responses are moderately heritable based on research using 42 Holstein herds across Canada. Also, several single nucleotide polymorphisms (SNPs) associated with antibody-mediated immune responses were identified in 58 Canadian Holstein herds suggesting that genome-wide SNP profiles may be used in the future to select HIR.
Thompson-Crispi, K. A., A. Sewalem, F. Miglior, B. A. Mallard. 2012. Genetic parameters of adaptive immune response traits in Canadian Holsteins. J. Dairy Sci. 95:401.
Thompson-Crispi, K. A., B. Hine, M. Quinton, F. Miglior, B. A. Mallard. 2012. Short communication: Association of disease incidence and adaptive immune response in Holstein dairy cows. J. Dairy Sci. 95:3888.
Genetic and epigenetic regulation of the bovine immune system. http://www.agweb.com/assets/1/6/High%20Immunity%20Bonus%20Content.pdf
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