Opinion by Price

Booster Vaccinations of Pregnant Cows with RB51
Charles Cl. Price, District III Commisioner of the Wyoming Game and Fish Commission

    In previous articles, I described a protocol that I believed could be used to booster vaccinate pregnant cows with RB51 vaccine without the risk of a significant loss to vaccine induced abortion.  These articles were published in the Wyoming Livestock Roundup on Jan. 1, 2011 (Brucellosis  – Strain-19 and RB51) and on June 25, 2011 (Brucellosis – Booster Vaccination with RB51).
    In the second article, I related the result for a small group, 20 head, which had received a RB51 booster shot as yearling heifers prior to being bred and were given a second booster shot as pregnant heifers in the fall of 2010.  The entire group of 20 heifers that received a second booster shot while pregnant carried their calves to term.  As proposed in the June 25 article, my son Kent Price and I booster vaccinated all of the bred cows that we retained for the herd at our fall 2011 pregnancy test with RB51.  All of these cows, numbering over 350 head, except one, carried their calf to term.  We had two dead before birth, and both appeared to be full term.  As for the one cow that was open we don’t know, she may have aborted or we could use the old fall back,  ”blame the vet.”  
    The important lesson was that any RB51 vaccine induced abortion caused by vaccinating the cows while pregnant was insignificant or nonexistent.
    One interesting thing that happened during this experiment was that all of our replacement yearling heifers carried their calves to term.  So much for the “blame the vet” theory.  Until these last two years when the yearling heifers have been RB51 booster vaccinated prior to breeding, we have always had a heifer or two slink their calf or show up with no calf by the end of the calving season.  This has led me to speculate that perhaps the RB51 booster prevents abortions caused by other aborting type diseases such as BVD or similar disease.  After all, the way the brucellosis vaccine works is to resist a brucellosis-induced abortion, thus minimizing the spread of the disease within the herd.
    In summary, the protocol that we have followed with RB51 is as follows. First, give the calf hood vaccination, which is a legal requirement. Then, booster vaccinate yearling heifers prior to breeding. Finally, give the first booster vaccination to cows that have only had a calf hood vaccination while they are open.  This allows us to booster vaccinate cows while we are doing our fall pregnancy testing.  A point to keep in mind is that we booster vaccinated our cows in about their second trimester of pregnancy.  I don’t know if a booster shot late in the pregnancy cycle would be a problem.
    In conclusion, we have demonstrated a protocol that allows booster vaccination of pregnant cows during their pregnancy testing with an insignificant loss due to vaccine induced abortion.  We have not addressed the time interval between booster shots that maintains this insignificant loss.  We are currently going to follow the state veterinarian’s recommendation of every third year.
    The important question regarding booster vaccination with RB51 is, will a cow properly booster vaccinated be able to resist an abortion caused by the field strain of brucellosis?  This is the critical question.  
    A challenge test of the RB51 and the booster vaccination protocol by the field strain of brucellosis is imperative.  We need to determine how effective the RB51 with booster vaccination is in controlling brucellosis.