Table 1.  Facts to Remember About MLV and NI Vaccines 

                                                               Killed-Inactivated 
Modified Live Vaccines (MLV)               Non-Infectious Vaccines 

1. Provide longer duration and                 1.  Provide short lived systemic 
 complete immunity than                               immunity. 
 (Non-infectious vaccines). 
 
2. Cellular and secretory                          2. Cellular and secretory 
 immunity should be produced.                    immunity poor. 
 
3. Do not require multiple vaccinations     3. Often require re-vaccination 
 for immunologic memory.                            to ensure immunologic memory. 
 
4. Often do not require revaccinating        4. Require multiple vaccinations 
 or require fewer revaccinations                    for active immunity. 
 during life of an animal. 
 

5. Rarely cause hyper- sensitivities,           5. Often cause hypersensitivity 
 but may be virulent for certain                       reactions. 
 individual animals or revert to 
 virulence. 

6. When used on pregnant animals           6. Cannot cause disease even in 
 some abortions will occur.                             immunologically compromised 
          animal. 
 

The following quotation regarding timing of vaccination by Dr. Schultz is also important. 

  "One of the most important considerations in designing a vaccination program, after the specific vaccines have been selected, is timing. When should the vaccine be administered?  Incorrect timing of vaccination is the greatest cause for vaccines failing to immunize.  Timing includes such considerations as:  1) the effects of maternal (colostral) antibody on active immunization, 2) the period of time between injection of vaccines that require multiple doses; 3) the age the disease most often occurs; and 4) the competence of the immune system, especially as it may be affected by age and stress." 

 A program that includes the use of MLV vaccines at weaning, then another booster at 12 months of age will be optimal in providing disease protection at the lowest cost.  The modified live vaccines given in this sequence should do a good job of protecting the heifer throughout her reproductive life in the cowherd.  In some herds the local veterinarian may encourage "occasional" revaccination, however the overall vaccine cost will be several times less expensive than boostering the cows each year with a “killed” product.  A word of caution: give the yearling MLV vaccination at least 30 days before the beginning of the breeding season. 

 There is an added bonus to changing to the MLV program.  Calf buyers are becoming increasingly aware of the health and performance benefits from cell-mediated immunity.  In a recently published report, Colorado researchers observed a $2.47/cwt. advantage for steer calves sold through the 1995 Superior Video Auctions if they had been put through the VAC-45 pre-conditioning program.  The VAC-45 program includes the pre-weaning and weaning immunization plus having the calves completely weaned and used to eating on their own. 

 Because MLV vaccines may cause abortion if given to pregnant cows or to calves nursing previously non-immunized cows, this program must be initiated carefully.  Visit with your local veterinarian about the use of these products and moving your herd towards the goal of  optimum herd protection with cell-mediated immunity.   For more information on this important topic, stop by your OSU County Extension Office and ask for OSU Fact Sheet F-9123 "Immunizations for Oklahoma Cow Herds".