MLV or killed vaccines: what’s best for your dairy operation?

Administering a well-planned vaccine program is the most cost-effective health investment a dairy producer can make, according to Mark van der List, BVSC, MPVM, senior professional services veterinarian for Boehringer Ingelheim Vetmedica, Inc., based in Davis, Calif.

Yet establishing vaccine protocols is a herd-by-herd scenario, he advises. "Successful vaccination -- which implies immunity from disease-- depends on the herd"s specific disease challenges, geography and management systems," says vander List.

There are differences in the types of vaccines that may be selected to manage a herd"s disease-prevention program.  Most vaccines fall into the category of either "killed" or "modified live (MLV)."

 In killed or inactivated vaccines, the pathogen for the target disease is contained in the vaccine but is no longer living. Modified live vaccines, on the other hand, contain living organisms that have been altered to reduce the virulence of the disease-causing pathogen. While still alive, these organisms have been rendered non-virulent by specific vaccine manufacturing techniques.  "A return to virulence in MLVs is possible but extremely rare," says vander List. 

 MLVs require the non-virulent pathogens to replicate in the animal, whereas killed vaccines do not.  Therefore, care must be taken when handling MLVs to protect the living organisms so the vaccines remain effective.

 To obtain an appropriate immune response from killed vaccines, these productsusually containadjuvants, which are additional compounds included in the vaccine. Examples of adjuvants include oil, saponins and aluminum hydroxide. These substances help stimulate the immune system to recognize the killed organism in the vaccine. To obtain an adequate immune response from a killed vaccine,vander List says initially two shots of the same killed vaccine, spaced three to eight weeks apart, are required. Yearly boosters then are recommended

The veterinarian says the advantages of killed vaccines include:

  • Extreme safety, with no risk of an organism reverting to virulence and infecting the vaccinated animal or its herdmates.  Killed vaccines also are safe for pregnant and immunocompromised animals.
  • Longer storage life and greater tolerance of field conditions than MLV vaccines.  MLVs, conversely, must be administered within one to two hours of reconstitution and may be damaged by heat, sunlight and cold.

MLVs, on the other hand, offer the following advantages:

  •  A stronger,cell-mediated immune response, plus the initial vaccination usuallyrequires only one dose to infer immunity.  However, because a small percentage of animals may not respond to a vaccine on a given day, it is recommended to repeat the vaccine at a later date.
  • Lower incidence of injection-site lesions, which sometimes can be caused by the adjuvants in killed vaccines.

"Using MLVs in pregnant cows is possible with some approved MLV vaccines, if the same vaccine was previously administered prior to breeding.  But this requires vigilant recordkeeping," notes vander List."If the health and vaccination history of a pregnant female is unknown, do not use MLV vaccines," he says, adding that MLVs also should be used no closer than three weeks prior to breeding.  This is especially important in heifers that may not have been vaccinated before.

Because dairies usually have ready access to their adult animals, killed vaccines may be practical, but the one-shot convenience of MLVs may be appealing for calves and heifers.  Van der List cautions, however, to avoid vaccinating calves at the same time as weaning, dehorning, castration, etc., as these stressful events may compromise calves" ability to respond fully to vaccines.

In some vaccines, MLV and killed organisms are incorporated in the same product, as is the case with Express® FP-10. Van der List says separate MLV and killed vaccines may be given safely at the same time.  But he recommends administering no more than two Gram-negative vaccines (such, Salmonella, E. coli, Leptospirosis and Mannheimia) in one session to avoid overloading animals with endotoxins. Clostridial vaccines also are included in this group.

Finally, vander List emphasizes the importance of vaccinating healthy, non-stressed, well-nourished animals (with adequate energy, protein, minerals and vitamins) to ensure optimal vaccine response.  "The herd veterinarian should be consulted to establish protocols that allow the herd to stay ahead of disease challenges, rather than respond to them after they occur," he says."The purpose of vaccination is to keep you from falling into a hole, not help you dig your way out of one."

To learn more about dairy vaccination protocols and disease prevention, visit

Boehringer Ingelheim Vetmedica, Inc. (St. Joseph, MO) is a subsidiary of Boehringer Ingelheim Corporation, based in Ridgefield, CT, and a member of the Boehringer Ingelheim group of companies.



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