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Immunity Doesn’t Come In A Bottle

Posted: January 24, 2008

Dr. Arlen Mills, Extension Veterinarian, Capital Region, Pa.
November 23, 2001

We often think that our livestock will be healthy if we can only find the right vaccine. Vaccination is important but natural mechanisms are an animal’s first line of defense against infections.  This would include things such as tears, saliva, enzymes, and the mucus lining the respiratory system.  Even the skin is an important protector for the body as it acts as a physical barrier to invasion by pathogens. This fact becomes particularly evident as we consider the teat end in the dairy cow.  Compromise the skin of the teat end and canal and mastitis results.

If a bacteria or virus gets past the physical barriers and invades the body, a second line of defense called inflammation goes into action. White blood cells attack and attempt to eat up the invaders. Dairy producers know these as somatic cells.

If these defenses are breached, the body has still another defense system which we refer to as the immune system. It is this system that we are hoping to enhance whenever a vaccine is given to our animals. When an animal is vaccinated, the body should respond by creating antibodies. But we know that this does not always occur. In studies done with feeder calves, as many as fifteen percent may fail to respond and be protected when vaccinated. There are a number of possible reasons for this vaccine failure, so let’s look at several major ones.

Genetics can affect the immune response. Compared to their ancestors, today’s dairy cow is highly inbred. While we have selected for various production traits, we have ignored the effect on the ability to generate a proper immune response. I suspect that we may have selected for some of the reproductive problems that we have as well. The first step in solving this problem is to recognize it.

In order for cattle to respond to vaccination or fight off infections, adequate nutrition is necessary. Adequate energy, vitamins, minerals, protein, and clean water is needed. We need to be reminded that the immune system places constant metabolic demands on the cow, and it is one part of the cow which never rests.

With the adoption of total mixed rations in the dairy industry, most producers do a good job of formulating and delivering a high quality diet. However, diets may not be reformulated during periods of stress or intake may decrease as happens in the prefresh cow. Then nutritional shortages may occur which short-circuit the animal’s ability to mount a strong immune response. Research has shown that nutrients such a copper, iron, zinc, selenium, and vitamins A and E can all have a great effect on the immune system. When one of these vitamins or minerals is deficient, it can inhibit the immune response
or cause an adverse reaction to a vaccine.

We know that all cows go through some degree of immune suppression in the week prior to freshening and for a week or two after calving. Some of this may be due to a nutritional deficiency as the cow eats less during this critical time. But part may also be caused by hormonal changes. Estrogen rises at this time and there is research to show that estrogen may suppress the immune system. The stress on the cow at this time also raises her level of cortisone which is an immune suppressor. For this reason I would not vaccinate a cow just before or soon after freshening. But any stress such as being
moved into a new pen, vaccination, hoof trimming, heat stress, and other management practices can all interact with nutrition and the immune system in detrimental ways.

Another big immune suppressor is acidosis. In the acidotic cow, abnormal rumen bacteria produce gram-negative toxins. These toxins depress the normal function of the cells of the immune system. Cows affected by subclinical acidosis are immune suppressed cows. The solution is obvious.

So when you have a “vaccine failure”, what is to blame? Rarely in my experience is it the vaccine itself. It is usually a failure of either timing, vaccine handling, or failure to respond due to one of the factors discussed. Vaccine strategies will be discussed in a forth-coming article.