Vaccination plays a key role in maintaining herd health and protecting cattle from disease. In the dairy industry, we deal with high-risk groups every day—cows that have just calved and newborn calves less than 75 days of age. While vaccines can be important, they are not always successful. Understanding why vaccines sometimes fail can help improve outcomes and protect the long-term health of your herd.
Herd immunity threshold (percent of animals that are immune) varies by the disease, but it usually means that 80 to 95 percent of the herd has antibody immunity to the virus or bacteria. How do dairy cattle get antibody immunity? They become infected and survive the disease, or we vaccinate them for the disease. The problem? Vaccination is not always successful. There are many reasons why a vaccine may not be successful, and many are within your control, but here are a handful of the reasons:
The animals may not be healthy enough to respond to the vaccine. Think of giving a vaccine to a sick animal or a fresh one. Sometimes we do not even know because it is during the incubation stage before any clinical signs. Monitoring cow health through a reliable cow health tracking system can help identify issues early and improve vaccination success rates.
The timing between the vaccine and when the disease breaks is too soon. I co-authored a presentation at the American Association of Bovine Practitioners on vaccines that work in the field. There are very few vaccines that have worked successfully in the field. The qualification to be approved by the USDA is only to show that it elicits an antibody response.
Mishandling the vaccine can reduce its potency:
The virus or bacteria is a different strain than the vaccine. For example, most IBR vaccines protect 2 strains of the virus and there is no cross-protection for the other strains. One dairy herd I work with closely has IBR Type 4 abortions. There are no commercially available vaccines that cover type 4.
Most vaccines require a loading dose and a follow-up (some require two follow-up vaccines). The spacing between these injections is important as well as the follow-up itself to get long-term immunity.
In young calves, some vaccines are blocked by the maternal antibodies. These come from colostrum and can be blocked for up to 4 months.
Not giving the vaccine often enough is a common issue. For example, the duration of immunity for the IBR vaccine is only 6 months. There is also a difference in the longevity of immune response between modified live vaccines and killed vaccines.
Giving too many vaccines at once can overload the immune system. I have seen a lot of dairy calves worked through a chute at dehorning that received the following: IBR, BVD, BRSV, Lepto 5, 8-Way Clostridia, and Bangs. That is 17 different vaccines that the animal is supposed to respond to. On top of that, the dehorning and work through the chute is traumatic and can cause corticoid steroid release that will also suppress responsiveness.
The use of too many gram-negative vaccines at the same time can suppress the immune response.
As you can see, there is a lot to think about. Improving herd health starts with proper vaccination protocols and dairy herd management. Regular dairy herd health analysis can help identify gaps in your vaccination program and improve outcomes. A reliable dairy farm management software can help track vaccination schedules, monitor cow health, and coordinate cow treatment more effectively. I would encourage a great discussion with your veterinarian to plan out how to improve your herd immunity and long-term dairy cattle health.