Resistance & Immunity

August 11 2009

By Peter J Lester

How does the body achieve resistance and immunity? 

It functions like this. The body's first line of defence is the skin, then the mucous membranes and the lining of the digestive tract. Pathogens cannot normally penetrate the skin, unless a break in this defence is provided via a wound. Sometimes they may enter via the sweat gland ducts or hair follicles, however they normally are not able to reach the deeper tissues via these routes. The sticky mucous secretions of the digestive tract, nose and lungs trap bacteria and prevent their spread. The mucous membranes themselves serve as a mechanical barrier for the entrance of unwanted bacterial proteins.

To achieve this sophisticated defence, the animal requires healthy defensive proteins, in the form of a healthy skin, mucous membranes and an ability to produce antibodies that release substances into the blood and tissue fluids in response to the presence of the foreign proteins called antigens. The body then reacts with this antigen, destroying it or neutralising it, and thus protecting it from the infection.

We can see from the above that we are dealing with an invading protein, an antigen, by the production of another protein called an antibody. Proteins, in brief, are made from Carbon, Hydrogen, Oxygen and Nitrogen, or CHON for short, it is known that most proteins contain 16% nitrogen in their structure. 

What then would happen if we just added more nitrogen to this equation? Obviously nitrogen on its own is not a measure of protein, but merely a factor in its calculation, all other prerequisites must be present and operating before this added nitrogen can be made into protein. If there is more nitrogen entering the diet than is necessary for the synthesis of cell proteins, the incoming amino acids, or un-combined potential protein substances are removed via the liver by a process termed deamination, to form urea and be eliminated via the urine. We see this as urine burns on the pasture. In the event that the incoming nitrogen is too large for the animal to process through its metabolic pathways, or it is in poor health, sick or injured, some of this nitrogen, often in the form of nitrite, (a substance produced in a rumen that has insufficient energy giving carbohydrates), enters the portal blood. 

Unfortunately, when we have too much nitrogen in the system, and insufficient energy to balance the equation, the excess N blocks off the conversion of carotene to true vitamin A. Vitamin A deficiencies in animals may be evidenced by weeping from the eye, retained afterbirth, decreased resistance to infectious disease, rough hair coat, night blindness, etc. This essential vitamin is necessary for the maintenance of the cells of the skin, the eye, and the digestive and respiratory tract. Vitamin A deficient cells become brittle and less resistant to infection.