Timing of 2nd Vaccinations
Dr. Chris Chase shared data at the recent Discover conference on calves, May 28-31 2013, about the timing of 2nd or booster vaccinations.
His data showed significant decreases in "B" cells starting around 16 days after the initial vaccine injection. He characterized the early phase of this drop in "B" cells as eliminating the weakest in this cell population. The more robust cells survive longer.
Based on this observation of differential decline in "B" cells his recommendation for second vaccinations is between 17 and 20 days. This captures the maximum anamnestic response (memory cells reproducing in response to the vaccine). Under field conditions, I would add, we have to remember that there is substantial variation among animals in their response to vaccines. This variation may be especially tied to calf health and level of nutrition.
This boils down to giving the booster injections sometime in the third week after the initial injection in young heifers. This timing increases the chances of getting the most immunity for the money!