By Gary Sliworsky, Ag rep, Emo
You probably had vaccinations as a child. They primed your immune system so that if the real infectious agent came along, you could clear it from your body without becoming ill.
Cattle are vaccinated for exactly the same reason.
To understand how the immune system responds to a vaccine, think of how your own immune system reacts to a ’flu bug. When the ’flu virus enters your body, your immune system detects the invader and begins manufacturing antibodies to neutralize it.
Once enough antibodies are in your blood stream, all the viral particles (antigens) are neutralized.
Antigens in a vaccine stimulate an antibody response in the same way.
The number of antibodies produced following a single vaccination often is too low to fight off the real infectious agent. A second vaccine given a few weeks later boosts antibody production to a higher, protective level.
The second vaccine is called a booster, yet is identical to the first one.
The timing of the second vaccine is critical. If it is given just one week after the first vaccine, the immune system already is in high gear so it can’t be boosted very much.
The antibody level will rise a little, but not as high as is needed.
If the second vaccine is delayed until eight weeks or more after the first one, the immune system already has backed off on antibody production.
Again, we will see a rise in the antibody level, higher than that stimulated by the first vaccine, but probably not enough to provide adequate protection.
Under some circumstances vaccines will fail. Among the reasons for this, the one considered the most important is stress.
Stress negatively affects the immune system, so more stress means a weaker immune system—and a poorer response to vaccination.
Stress has a very real effect on animals. Calves vaccinated when they enter a feedlot provide a classic example. They are injected after being stressed by transportation, socialization, and adaptation to a new environment, as well as by having a change in feed and by being exposed to animals from different sources that carry infections.
These calves can’t be expected to mount an effective immune response quick enough to be protective.
It is better to administer vaccines when animals are not stressed. Ideally, it is done at least two weeks prior to the anticipated exposure to infectious agents.
Maternal immunity is another reason for a poor response to a vaccine. Antibodies derived from the dam’s colostrum inactivate the vaccine before the calf needs to react to it.
Maternal antibody levels eventually fall to non-interfering levels, and eight weeks of age generally is considered sufficient to avoid this problem.
The effect of maternal immunity is different for each type of vaccine. Modified-live vaccines produce an immune response at an earlier age than killed vaccines.
As well, intranasal vaccines produce a response earlier than intramuscular vaccines.
Most label directions suggest adult cattle should be given one vaccination and a booster 14-28 days later. Calves less than six months of age also should have a booster.
Annual revaccination also is recommended for most vaccines.
If you are still in doubt after reading the label, ask your veterinarian how the product should be administered to ensure optimal immunity.