As summer draws to a close, we can see that weaning time is on the horizon. Though weather conditions are more favorable for weaning this year compared to last, weaning is still the most stressful event a calf will likely experience. And since stress decreases immune function, it is imperative that as cow/calf operators we time our vaccines so they can be the most effective for the calf. This begs the question, when is that optimum time to vaccinate calves for weaning?

The answer comes from understanding how vaccines help the calf’s immune system. What a vaccine does is give an inactive form of the disease to the animal, to which the animal’s immune system identifies and creates cells that “remember” the disease. This way, when the actual disease arrives, the immune system already has specific cells for defense against this disease. This process takes a week and a half to three weeks, depending on the individual animal’s immune system, the specific disease the vaccine is for and environmental factors.

With this in mind, since weaning creates the stress that hinders the immune system, allowing the disease (in this case, pneumonia) the chance to proliferate, our best time to vaccinate is prior to weaning if our goal is to prevent disease. By vaccinating three to four weeks before weaning, the calf’s immune system has time to mount an effective response to the vaccine, preparing it for the rigors of weaning.

The downside is that this may be difficult to achieve for some cow/calf producers. Cattle may be out on pastures far from home where working facilities are not present. Silage chopping or harvest may run long, absorbing all the hours present in the day. In this case where vaccinating prior to weaning is not possible, is it better to give vaccinations at the time of weaning or waiting until the calves are fully weaned?

It is not possible to give an answer that works for 100% of producers, because each situation is different. I would recommend you work with your veterinarian to receive guidance before you vaccinate your calves.

That being said, recent data provides an interesting observation. A study done by the University of Arkansas compared vaccinating freshly weaned calves on arrival at a feedyard with delaying the vaccination. The delayed vaccination calves actually performed better than the calves vaccinated on arrival.

The likely cause of this situation is vaccination works best in healthy, low-stress cattle. By vaccinating on top of the stress of weaning, the vaccination isn’t able to stimulate the immune system as appropriately. Therefore, it may be best to wait until the calves are fully weaned and on feed before vaccinating them.

One way to accomplish this is to wean the calves, start them on feed and then run a feed-grade dewormer through the group. This deworming is helpful, because internal parasites sap energy from the immune system that could be used to fight pneumonia. Then, at thirty days post-weaning, vaccinate the calves. While the vaccine may not be on board for the weaning process, it will be present to help prevent pneumonia during adverse weather events later in the feeding period.

With vaccine administration, timing is everything. To help prevent pneumonia at weaning time, the gold standard is to vaccine the calves roughly a month prior to weaning. If this isn’t possible, then it may be best to just deworm the calves at the time of weaning, and then wait until the weaning process is fully completed before vaccinating the calves.

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