A proper vaccination protocol is a key component (or should be) of all herd health management programs. A big question is always what are the differences between killed vaccines and modified live vaccines and which one is best? Let’s take a minute to learn about some key advantages/disadvantages of both forms of vaccines and provide some scientific insight so you can make vaccination choices that fit your needs! There is a lot to know about MLV and killed vaccines, these are the main points for you to consider. As always it is best practice to develop a relationship with your veterinarian who can be your primary guide for your herd’s vaccination program.

Modified Live Vaccines (MLV): Contain a small amount of virus or bacteria that is altered so to not cause disease. These vaccines cause these organisms to replicate in the animal to cause a controlled infection. In turn, the animal’s immune system produces a response to this replication for future protection against said organisms. MLV are available primarily for diseases caused by viruses.

Advantages of MLV:

• One dose is often sufficient for protection.
• Can elicit a faster, stronger, and longer lasting immune response.
• Less costly.

Disadvantages of MLV:

• Risk of abortion in pregnant cows if not used per the label.
• Requires extra precaution and proper storage.
• Must be used within about 30 minutes of mixing the vaccine.
• Some MLV not approved for use in calves nursing pregnant cows.

Killed Vaccines: Also referred to as an inactivated vaccine, a pathogen for a disease is within the vaccine but is no longer living. To obtain a proper response adjuvants, or additional compounds such as saponins or oils must be included in the vaccine. Killed vaccines are safe to use in any animal regardless of pregnancy status.

Advantages of Killed Vaccines:

• Less risk of an organism reverting to virulence.
• Safer for pregnant or immunocompromised animals.
• Longer shelf life and no on-farm mixing.

Disadvantages of Killed Vaccines:

• Booster doses required (Another time cattle must be handled)
• Slower animal immune response.
• Broad-spectrum immune response is lower in some strains of disease.
• Allergic reactions are more common.

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