Building better immunity: Calf and cow vaccination strategies that work
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EmailUnderstanding the developing immune system in young calves is key to effective health management. Calves benefit from dam immunity via colostrum and prenatal vaccines, but no shot can compensate for poor management or stress.
Vaccines are one of the most powerful tools for preventing disease and supporting lifelong calf health, but they’re not a silver bullet. In a recent Heifer Academy webinar, Angel Abuelo, DVM, Ph.D.,Red Cedar Distinguished Professor at Michigan State University, broke down the science behind immunity and vaccinations in young calves. His insights revealed how well-timed vaccines, combined with sound management practices, can significantly reduce disease risk and improve performance over the lifetime of the animal.
At the outset, Abuelo emphasized a foundational principle: vaccines cannot fix poor management. While vaccines can enhance immunity and reduce disease incidence, they won’t work if calves are not housed, fed and cared for properly. Calves under stress from cold, overcrowding or poor nutrition may be unable to mount an effective immune response even when vaccinated. Producers must view vaccines as one part of a broader strategy, not a shortcut or replacement for good husbandry.
Understanding the immune system in young calves
Calves are born with immature immune systems and no circulating antibodies. Because the ruminant placenta blocks the transfer of immunoglobulins in utero, calves are completely dependent on colostrum to receive passive immunity. While they are born with the full complement of immune cells, those cells are inexperienced and slower to respond. Abuelo outlined how the immune system functions in two main branches: innate immunity and adaptive immunity. Innate immunity offers a fast, non-specific response to pathogens and includes physical barriers like skin, as well as immune cells like neutrophils and macrophages. Adaptive immunity, on the other hand, is slower to activate but more precise, generating memory cells and antibodies that protect against future infections. Vaccines primarily target this adaptive response, training the immune system to recognize and react quickly to specific pathogens.
One of the most effective ways to support calf immunity starts before the calf is born. Strategic vaccination of the dam during the dry period enhances the quality of her colostrum, providing the calf with higher levels of pathogen-specific antibodies. Vaccinating the dam has proven effective against common diarrheal pathogens such as E. coli, rotavirus, coronavirus and Salmonella in calves. Abuelo also shared findings from a recent study showing that vaccination of Salmonella Dublin carriers reduced the risk of intrauterine transmission by more than fivefold. This kind of targeted strategy not only benefits the calf but also reduces the spread of zoonotic pathogens within the herd.
Timing is critical for vaccination efficacy
Colostrogenesis, the process by which antibodies are concentrated in the colostrum, begins about four weeks prior to calving, but the bulk of immunoglobulin transfer occurs in the final week before birth. To maximize the effectiveness of maternal vaccination, any booster doses should align with this window. That means initiating the vaccine series at least five weeks before the expected calving date, states Abuelo. Before making changes to your vaccine schedule, consult your herd veterinarian.
Calf vaccination: Timing, type and strategy
When it comes to vaccinating calves directly, timing and method matter. Abuelo noted that some intranasal vaccines can be given shortly after birth and can be effective in stimulating localized mucosal immunity, particularly IgA production in the respiratory tract. Mucosal immunity works to prevent the attachment and penetration of microorganisms. Vaccines of this classification act quickly and can help prime systemic responses as well, though they still require time to be effective.
Injectable vaccines are more dependent on the calf’s developing immune system maturity. A meaningful antibody response to injected vaccines typically does not occur until calves are at least three to four weeks old. However, calves can still mount cell-mediated immune responses earlier, even in the presence of maternal antibodies. For many years, it was believed that maternal antibodies blocked vaccine efficacy. Abuelo clarified that while these antibodies may interfere with B cell (antibody-producing) responses, they do not suppress T cell-mediated immunity (destroy infected cells directly), which is also critical for protection.
Another key point was the importance of spacing out vaccine doses. Traditional recommendations and labels often suggest a two-week interval between the primary and booster doses. However, new evidence indicates that a longer interval, closer to three or four weeks, results in stronger immune memory. Vaccinating too frequently can lead to T cell exhaustion, reducing the effectiveness of the immune response over time.
Choosing between modified live and killed vaccines
As identified by the American Associate of Bovine Practitioners, there are five categories of vaccines. When choosing a vaccine, the question often arises: should you use a modified live or a killed vaccine? Abuelo explained the trade-offs between modified live (MLV) and killed vaccines. MLVs generally produce a more robust and long-lasting immune response, particularly for pathogens that require a strong T cell response. However, because they contain a weakened form of the live pathogen, they should not be used in immunocompromised or pregnant animals unless prior immunity has already been established.
Killed vaccines are still effective without a weakened live pathogen, especially when paired with appropriate adjuvants, a substance that enhances the body's immune response to an antigen. These are preferred in situations where safety is paramount, such as in naïve or pregnant heifers and cows. The decision between vaccine types should be guided by the pathogen in question and supported by the herd veterinarian. For example, intracellular pathogens like BVD or BRSV benefit more from MLVs due to the need for cell-mediated immunity, whereas extracellular pathogens may be well-handled by antibody responses alone, according to Abuelo.
Tailoring vaccination programs to each farm
Finally, Abuelo emphasized that no two farms are exactly alike. Disease pressure, housing conditions and pathogen strains vary widely, which means vaccination programs must be customized. Regular testing, accurate recordkeeping and monitoring disease trends over time are essential for adjusting protocols as needed. Over time, producers should not only add vaccines when new threats arise but also be willing to retire vaccines that are no longer relevant, avoiding over-vaccination, which can stress the immune system and reduce animal performance.
Vaccines are a critical part of a comprehensive health program, but they work best in harmony with excellent management, targeted disease surveillance, and strategic decision-making. “Vaccination isn’t just about giving a shot, it’s about understanding when, why and how to protect calves from the start,” Abuleo said.
If you are interested in learning more about this topic, or would like to read the published articles on the subjects talked about today, please reach out to Angel Abuelo, DVM, Ph.D.