Kris Ringwall this week posted a really nice explanation of immunity as it relates to vaccines, and I'd like to share that and expound a bit more.

Ringwall is director of the Dickinson Research Center for North Dakota State University and has done some good research on cow size and resulting calf size. We've quoted that before on more than one occasion.

Ringwall reminded his readers the purpose of vaccination is to create antibodies that are specific to organisms that create a major threat, or a particularly dangerous one. Those antibodies then remain in the body ready to attack an invading organism like the old Pac-Man icon did in one of the first mass-produced computer games in the 1980s.

A recent blog by a North Dakota educator compares antibodies with Pac-Man, which brings the author to ask whether every cow needs a Pac-Man game.

Ringwall said, "The basic concept of immunity is relatively simple. The body reacts to foreign objects by developing defensive antibodies. Whenever I bring up the topic of immunity, I cannot help but be reminded of the old game of Pac-Man, a computer game created in 1980 by Toru Iwatani while working for Namco, a Japanese company.

"Pac-Man was a circular object with a large mouth that had only one function:

catch and consume little dots. Pac-Man would move up and down channels not much different from our circulatory system's arteries or veins, systematically removing all the dots. Pac-Man, a large body chasing little dots, was not that much different from nature: the large 'antibody' in the circulatory system chasing and eating small dot-like intruders."

Of course, to complicate matters, the more aggressive organisms are best attacked by their own specific brand of Pac-Man, so it helps to have those present in the body.

Ringwall also noted that immunity changes constantly and the amount of pathogen-specific Pac-Men tends to decrease over time. Therein lies the concept of re-vaccination, or booster shots.

He also noted individual cattle differ in their levels of immunity to each pathogen. Some cattle have much higher immunity, some are able to maintain higher immunity, some get more exposure and some get less. The same could be said about parasites and natural immunity, although I can't think of any vaccinations for parasites, unless you want to include the protozoa Trichomoniasis.

Ringwall went on to explain the concept behind herd vaccinations very well, I think.

"The goal is to build an acceptable level of herd immunity to the disease-causing pathogens so outbreaks are isolated cases and the cattle population remains healthy. A broad vaccination program builds immunity within the general population, effectively limiting the capacity of pathogens to spread freely," he said.

Ringwall added this does not mean a complete absence of pathogens, nor can it create an elimination of disease outbreaks. The intent is to limit susceptibility.

If the animals are never exposed to the organism, then the vaccine's response of creating immunity will never be used.

This leads to the idea of biosecurity and the concept of a closed herd with limited outside exposure.

People who choose not to vaccinate for most or sometimes all pathogens usually are banking on a combination of a closed and relatively isolated herd, together with whatever natural immunity is present in the herd. Apparently it can work, because I regularly run across people who have extremely limited vaccination programs and very low death loss. Most of these folks recognize their losses will be considerably higher if there is an outbreak, but weigh it against the costs of vaccination, handling and some sickness and loss from the actual vaccinations.

I hope to explore these concepts more in coming months, but I always have two questions about these herds and their calves which I would like answered.

1. What happens when calves are sold off the farm/ranch and they go into the normal flow of cattle, which by almost any measurement is highly contaminated with the very worst pathogens.

2. Isn't it worth vaccinating against the few diseases like Blackleg, which don't seem to be highly prevalent in the environment, but may appear more often in situations that create stress, such as drought? Aren't cattle at a big disadvantage when these things happen?

Hopefully, I can get some good materials put together on this for upcoming issues of Beef Producer, BEEF Vet, and the websites.

In the meantime, I would surely like it if you readers would share your ideas on these topics.