Mother Nature does an excellent job of passing down immunity to calves from their dams, provided that the dam’s colostrum is rich in antibodies, the calf gets it at the critical early hours after birth, and the calf gets sufficient volume.

Jim Roth, DVM, PhD, Iowa State University, says the length of time a calf is protected depends on those factors. “The protection might last for six to eight months,” he says. “However, if the cow did not have antibody or the calf did not get colostrum, there won’t be any protection after birth.”

Getting good colostrum in the first place can be enhanced with good cow vaccination. Vaccinating the cow is very important for increasing her antibody titer. That results in more antibody in the colostrum, higher antibody titer in the calf and longer duration of immunity in the calf.

Some practitioners and producers have seen illness in calves within a couple of weeks of vaccinations and some place the blame on the vaccines, but it’s important to understand immunologically what’s going on during those times. “Illness within two weeks of vaccination may be a coincidence,” says Roth.

“Illness could also be brought on by stressors that occur at the time of vaccination, like weaning, castrating or dehorning. Stress can suppress the immune system and allow subclinical infections to become clinical. Vaccination itself is a stress on the animal’s immune system. Giving multiple vaccines at the same time, along with pour-on, implanting and parasite treatment, adds to the stress.”

In addition, he notes, exposure to infected animals when the calves are rounded up and confined for vaccination can result in clinical disease. “The incubation period for many diseases would result in illness within two weeks of vaccination. Vaccines take a couple of weeks to induce immunity, so they have not had time to protect the calf that is stressed and exposed to disease at the time of vaccination.”

Because of this, the timing of calf vaccinations is important. The immune response takes at least two weeks to protect the animal. If the vaccine is a two-dose product, you can’t expect protection until two weeks after the second dose. In order to protect the animal at the time of weaning when it is most vulnerable, it needs to be well-vaccinated at least two weeks before weaning. “Vaccines are tested and shown to be effective in non-stressed animals,” says Roth. “Vaccination at the time of stress can reduce their effectiveness.”

Vaccines and stress aren’t the only factors that influence the immune system for the good or bad. Vitamins and trace-minerals are very important for immune function. Often, the immune system is the first system impacted when an animal has vitamin deficiency or trace-mineral imbalance. “Their immune system can be suppressed, resulting in increased susceptibility to infection before other symptoms of deficiency occur,” adds Roth.

Roth sums up the most important points for optimizing the calf’s immune system at preweaning and weaning times:

  • Vaccinate at least two weeks before weaning.
  • Minimize stress at the time of vaccination and at weaning. Some stress is inevitable, but it should not all be piled on at once.
  • Avoid exposure to infectious agents from mixing and crowding animals.

Read the full article on weaned calf health in Bovine Veterinarian here.