A common question veterinarians receive in the fall is when and if calves should receive booster shots. Despite advances in vaccine technology, there are still some vaccines that work the best with a booster. Pinkeye and Histophilus are ones that come to mind for me. If you have these in your protocol, you should probably figure on giving a second round of vaccines.
There are two principles that guide the decision to give a second shot. The first immunological principle is that only 70% of cattle respond to the first vaccination. The second is that those who respond the first time have a better immune response with a second shot. That being said, the timing of the booster vaccinations impacts the amount of immune response the calf has to the shot. In addition, the act of being vaccinated can cause unintended, negative consequences if done at the wrong time.
Traditionally, in the cattle business we have considered a booster shot two weeks after initial processing to be a good practice. However, from both reasons stated above I would challenge that assumption. First, consider the immune response of a calf who does not finish reacting to a vaccination for three weeks. This means if we re-vaccinate two weeks later, we do not receive the full benefit to the immune system of the booster vaccine.
The second reason is more concerning. When we vaccinate cattle, we take them out of the pen where they are accustomed to being to work them, thereby messing up their regular eating and drinking schedule. This isn’t a big deal if the cattle are on a consistent ration and have been consuming it readily.
But most vaccination occurs in cattle on arrival at the feedyard. When we pull cattle from the pen at two weeks after initial processing, we are interrupting their eating pattern at the same time we are stepping them up on feed. We couldn’t have worse timing, as inconsistent intakes lead to acidosis, bloat and predispose cattle to pneumonia. It is not uncommon for cattle processed during this critical time period to actually break with the very diseases they are being vaccinated against.
Instead of giving booster vaccines at two weeks, it is preferable to wait three to five weeks. This gives the calves’ immune systems adequate time to fully process the first vaccine. For calves processed at arrival or soon after, it is best to wait until 30 days on feed to give the second round of vaccines. This will give them a full month to stabilize their consumption on the grower ration, with minimal up and down variation.
And in general, for booster vaccinations I would be very selective about the environmental conditions the day the cattle are worked, as well as the two days before and after that day. Weather fluctuations lead to inconsistent intakes; why compound the issue by pulling cattle from the pen? Rather, pick a time when the weather is mild (by Northern Plains standards at least) and do the boosters then.
On a side note, it may be beneficial if booster shots are to be given to implant those calves on the second trip through the chute instead of the first. Since intakes are more consistent after 30 days on feed, the calf is more apt to utilize the full value of the implant at that time.
Booster shots benefit calves in some situations, due to the way the immune system reacts with certain vaccines. That being said, we should take care to time the booster vaccines so they do the most good for the calf and do no harm. Plan on working those calves at least three weeks after the initial vaccines, or after 30 days on feed, to give your calves the best opportunity to mount an effective immune response.