A LIVESTOCK VACCINE PRIMER

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The classic example of passive immunity is the disease resistance passed by a mother to her offspring, via the colostrum (first milk). Mankind has created another way of passing on short-term resistance, using antiserum injections. Such medicines (which are made from the blood serum of an animal that already possesses a particular immunity) offer effective quickfix protection against canine distemper, feline panleukopenia, human measles, and many other diseases.

Another category of passive immunity medicines, antitoxins, fight the poisons that some "bad-guy" bacteria produce. . . specifically when such "waste" substances — and not the germs themselves — are deadly. (The relationship between a toxin and its parent bacteria is similar to the connection between thick smoke and fire: The flames cause the billowing clouds . . . but, in many cases, those fumes can be more dangerous than is the blaze itself.)

The members of the Clostridia bacteria family are about the most notorious toxin producers. And the most infamous member of this clan is Clostridium tetani, or tetanus. Anytime one of your critters — especially a horse — gets a severe cut or has open surgery, you should administer tetanus antitoxin to the animal for its immediate protection. (Another common killer "cousin" is Clostridium perfringens, or the overeating disease.)

ACTIVE IMMUNITY

The animal itself must develop an active immunity. This form of disease resistance is sort of like the left jab/right cross combination I learned as a boy. I haven't had to physically defend myself for some years now, but I believe I could still use the technique effectively . . . if I absolutely had to (well, at least if I were up against a smaller and weaker foe!).

An active immunity takes time to develop, is long-lasting, and is a result of "experience": that is, an animal builds the antibodies that combat the disease only after first catching — and recovering from — the illness. A vaccine, of course, uses this exposure technique to help livestock create disease resistance. Often, though, the critter will require a booster application of the same treatment every year or so, to refortify its disease-fighting ability. (In a similar way, I could very likely use a periodic workout in the gym if I really wanted to be prepared to counter a physical attack.)

ATTENUATED AND KILLED VACCINES

Now let's say that you have a litter of newborn puppies, and you want them to develop long-lasting immunities to distemper. Well, you could squirt a strong dose of that virus into the pets' pen and figure that any pooches that survive the resulting mini-epidemic will henceforth have a strong resistance to the disease ... but that solution would be worse than the problem!

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