The incredibly thin line between sickness and health in calves

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The incredibly thin line between sickness and health in your calves

Most of us have heard that the ability of a cow to digest her food is largely dependent upon the presence of enormous numbers of bacteria in the rumen. But we also have probably been told on at least on occasion by our veterinarian that a calf died from “environmental” bacteria, such as E coli or salmonella. That is, a bacteria normally present in the digestive tract of the calf somehow “got loose” in the calf, and became pathogenic (that is, made the calf sick). Today I’m going to talk about that in some detail.

This week I’m attending the annual conference of the American Society for Cell Biology. This organization’s membership consists of research scientists from all over the world; they all have in common the fact that they do research in cell biology. So what has that got to do with calves? Well, simply put, everything. But of all the presentations on seemingly arcane and (to non-scientists) incomprehensible lectures discussing the latest research into how the cells in everything from bacteria to humans work, there was one presentation that really “hit home” in regards to baby calves. I’m going to try to briefly relate to you the essence of that presentation, because it really highlighted just how incredibly close your calves always are to being sick and then dead!

Dr. Lora Hooper, of the Departments of Immunology, Microbiology, and the Cancer Immunobiology Center at the Univerisity of Texas Southwestern Medical Center, is a research scientist whose work is funded by the privately funded Howard Hughes Medical Institute, the Burroughs Wellcome Foundation, the Crohns and Colitis Foundation, the Welch Foundation, and the governmental agency, the National Institutes of Health. In other words, a lot of folks with lots of money in their pockets trust Dr. Hooper’s work enough to give her millions of dollars every year to study the bacteria in the intestine of humans (and indirectly of animals such as cattle).

Over the past few years Dr. Hooper, and the fourteen scientists and lab technicians who work for her have been working to discover exactly what goes on in the intestine that prevents the bacteria normally in the intestine from leaving the interior of the intestine and causing the person or animal to become sick. It is certainly not because the bacteria signed a “non-aggression” treaty!

You may know that the bodies of both humans and calves are made up of approximately 100 trillion cells. That is an incomprehensibly huge number: 100,000,000,000,000. But the number of individual bacteria in your intestine is between 10 times and 100 times larger than that! So, in the battle between you (or your calf) and the bacteria, you are out-numbered 100 to 1! But the odds are actually much, much worse, because the total number of cells that make up the lining of your small intestine is only a very tiny fraction of all the cells in your body! So every single cell in the lining of your intestine must defend against literally billions of bacteria. So how does this work?

What Dr. Hooper has discovered is that each cell in the lining of the intestine can emit a “slime” (mucus).  Here is how this works: you may rub a sun screen lotion on your exposed bare skin before you go outside and are exposed to sun light all day. You “sense” a threat – you know that if you are outside all day in bright sunlight, you will get sunburned, so you do something to prevent being sunburned (you put on sunscreen lotion). In the same way, when the cell senses that bacteria are approaching it (the threat), the cell “puts on” a “bacteria screen lotion”.

Now, you know that when you put on the sun screen lotion, that layer of lotion on your skin is extremely thin – often thinner than a single sheet of paper. In the same way, the “bacteria screen” that the cell covers itself with is incredibly thin – in scientific terms it is 50 nanometers thick – in everyday terms it would take several million layers of this “bacteria screen” to form a layer as thick as a sheet of paper!

If anything causes that super, super, thin layer of  “slime” to be removed from the surface of the cell, or causes the cell not to produce that thin layer every time a bacterium approaches the cell, then the bacteria will attack the cell, likely destroying the cell and thus entering the blood stream. Dr. Hooper’s research has determined exactly what chemicals are involved in what turns out to be a complex series of chemical reactions in which the cell determines that the bacterium is nearby, and responds by emitting the “slime” that protects it by causing the bacterium to move away from the cell.

I’m not going to go any deeper into this topic here, but I do want you to remember just how thin a line exists between your calf being healthy and being sick with scours: it would take a few millions of those layers to make a sheet of paper.

So why does the calf sometimes get sick, but usually not? Dr. Hooper’s research does not address that question, but here is one obvious way that the protective layer of “slime” can be broken: something other than a bacterium enters the small intestine, such as coccidian organisms or (perhaps more likely) Cryptosporidium parvum. These things are NOT bacteria, and they are not sensitive to the antibacterial mucus produced by the cells in the intestine.

Now, the protective layer of mucus is not perfect, and occasionally a few bacteria do get through the surface of the intestine, but in healthy calves (or people) the immune system takes over, identifying the invader and destroying it. It is only when too many bacteria get through the protective layer that the calf (or you) gets sick. Sometimes those unusual bacteria in effect wear camouflage to “hide” from the immune system, but typically 10,000 or more individual bacterium must invade at the same time to win the battle with the immune system, and fortunately that does not happen too often.

In contrast, it has been demonstrated that two Cryptosporidium parvum oocysts are capable of causing a severe or fatal infection, because the baby calf has no “built in” immunity to Cryptosporidium parvum. Within a few days of the initial infection the Cryptosporidium parvum has multiplied millions of times, destroying enough cells in the lining of the intestine to “open the door” to a huge number of bacteria, which in turn cause a fatal infection.

And this leads me to an argument as to why you should NOT use recycled sand as bedding in maternity areas: Cryptosporidium parvum is extremely resistant to nearly all methods of “cleaning” recycled sand, except the physical abrasion of sand particles against each other. That is, unless you are lucky that every single oocyst is literally crushed between two sand grains, that oocyst is likely to survive the recycling process and still be in the sand when it is put into the maternity area. Then, when the newborn calf’s mouth first hits the sand, the oocyst gets in the calf, and 10 days later the calf is sick.

About the Author

Roy Williams
Roy is a retired calf grower, and is now a graduate student in the Molecular and Cellular Biology Program at Dartmouth. He is currently involved in research in the genetic factors of cancer at the Geisel School of Medicine at Dartmouth. His long-range research interests are in parasitism and infectious diseases, particularly in calves.

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