Source: Dairy Calf and Heifer Newsletter
Whether it’s a dairy calf, human infant or baby giraffe, all newborns enter a “dirty world” that is filled with “germs,” viruses, bacteria and other microorganisms – many of which cause disease. Fortunately, Mother Nature provides health protection through maternal antibodies and maternal colostrum. And, “science” steps in to build on this protection via injectable vaccines.
During the Dairy Calf and Heifer Association’s Annual Conference, John Ellis, a professor at the University of Saskatchewan’s College of Veterinary Medicine, addressed using vaccines to improve Mother Nature’s plan for immunity in cattle. His primary research interest lies in the development and efficacy testing of intranasal and parenteral vaccines for respiratory infections, including Bordetella bronchiseptica in dogs and bovine respiratory syncytial virus (BRSV) in calves.
“Protection from disease is a multi-step immunological process,” Ellis explained. “Colostrum management is a first essential step in protecting young cattle from infectious disease and establishing a foundation for immune responses later in life.” Remember, a calf should receive about 2 liters of high-quality colostrum as soon as possible after birth – definitely before 12 hours of age. Whether you feed maternal colostrum or a high-quality colostrum replacement product, make sure it’s high in antibodies (immunoglobulins). “Immunoglobulin (Ig) G1 is the most important antibody in colostrum. The timely use of vaccines in the cow can increase the amount and quality of IgG1 in the colostrum.”
Ellis noted that passive immunity (gained from maternal antibodies and colostrum) is rarely an “all or none” phenomenon, but rather a sliding scale or bell curve, unless the calf receives no colostrum. “Good calf husbandry can enhance the absorption process,” he said.
Boosting resistance naturally
The second essential “ingredient” in protecting young cattle from infectious disease comes via natural exposure to germs – both in the environment and those shed by immune adults. “This process of exposure to germs in the presence of maternal antibodies is an important first ‘free vaccination’ for calves,” said Ellis. This natural exposure occurs at mucosal surfaces (lining of respiratory and gastrointestinal tracts) and effectively “overrides” maternal antibodies and results in “priming” the calf’s immune system. “This is a necessary step in developing ‘active’ or ‘adaptive’ immunity in calves and other neonatal animals.”
Once a young animal has been effectively primed, the third part of Mother Nature’s plan kicks into gear – boosting the primary responses. Ellis explained that boosting a single primary exposure is needed because young immune systems are not mature and only one exposure typically does not result in long-lasting immunity. He noted that immunity is rarely complete. Usually, exposed individuals develop “clinical immunity” that prevents or reduces disease but does not completely prevent infection or “shedding” of germs via nasal secretions or feces. Thus, ordinary, day-to-day interactions provide opportunities to boost primed responses. “Overall, this process contributes to ‘herd immunity’ or overall population immunity,” said Ellis.
Colostrum: First line of defense
To summarize, Ellis emphasized the importance of colostrum management. “Without optimal passive immunization, subsequent vaccination will most often be futile – a waste of money – because the calf will either succumb to E. coli diarrhea or be too unhealthy to respond most effectively to vaccines,” he stated. You can improve colostrum quality with timely vaccination of cows through modified-live vaccines prior to breeding or with inactivated vaccines three weeks prior to calving.
Second, Ellis said to prime calves early in life through mucosally delivered vaccines – intranasal or oral. “Effective, combination intranasal vaccines are available for important respiratory pathogens in calves, including BRSV and parainfluenza-3 virus,” he said. Ellis prefers using intranasal vaccines containing temperature-sensitive bovine herpesvirus, due to safety concerns.”
“Oral vaccines for bovine coronavirus (and rota-virus) are probably most effective if administered intranasally,” he noted. “Some will be swallowed and some will more effectively expose the respiratory tract. Traditional approaches aside, do NOT use injectable vaccines in passively immune animals and expect to get much priming of the immune system. Just as maternal antibodies protect, they effectively block most effective priming of immune responses.”
And third, boost primed responses with injectable vaccines at about 2 months of age. “The choice of vaccines to most effectively achieve boosting will vary with the pathogen,” Ellis commented.
As a final note, Ellis stated, “At a time when there’s increasing concern about antibiotic use in food animals, and, relatedly, the development of antibiotic resistance in humans and veterinary patients, more timely and judicious use of vaccines will not only improve calf health but also address consumers’ food safety concerns.”