Any astute cattleman knows that he cannot change feed sources on his herd quickly; he must gradually blend the new feed with the old over several days. If he doesn’t do this, he runs the risk of creating health issues for his animals, such as bloating. This is particular problematic in the spring when moving the herd from dry hay onto lush green vegetation.

This is because cattle rely heavily on intestinal microorganisms (bacteria, fungi and protozoa) to “digest” their food – most notably the complex carbohydrates associated with fibrous plant material. Because microbes, such as bacteria, usually have very specific food requirements, the appropriate ones needed to adequately digest the “new” material may not be present in sufficient numbers, and, therefore, will require a few days to grow out. If that time isn’t given, the result can be undigested food in the cow’s gut which can lead to constipation, diarrhea, bloating, etc. Sound familiar?

Yes, though our digestive processes seem less dependent on microbes, similar things can happen to us as well.

When I was a young assistant professor at Creighton University Medical School our understanding of the potential benefits of bacteria in the gut was just beginning to develop. We would talk about “good” bacteria, and how they helped prevent establishment of disease causing ones; but that was all we knew at the time.

Fast forward 50 years and that picture has become both clearer and more complicated. A better understanding of both the sheer number of gut microbes, as well as their enormous diversity, has emerged.

Current estimates are that in the adult human colon the number of bacteria per gram of tissue is in the range of 1011-12 (that’s a number “1” with 11 or 12 zeros after it). Since the whole colon averages 1,000 grams, we can add four more zeros to estimate the total number of bacteria in a typical human colon – 1,000,000,000,000,000. That’s a number which even makes the national debt look trivial.

Estimates of the number of different species of microbes present in an individual human intestine range from 300 to 1,000; while one estimate for the number of species represented in the whole human population is 35,000. Did most of you even imagine there were that many different species?

Most of those species are strict anaerobes (they cannot survive in the presence of oxygen). Since techniques for the isolation and cultivation of anaerobes are difficult at best, those numbers could prove to be gross underestimates.

So how does one fit the information being provided for the single species often offered as a pro-biotic into this emerging complexity? Very carefully I would suggest.

Finally, while protection against invasion by disease causing microbes (pathogens) remains a beneficial quality, other, even more fundamental interactions, are coming to light.

For example, since the total surface area of the human intestinal tract is estimated to be about the size of a football field, the gut represents a major point of contact between a person and the external environment.

Accordingly, a complex role is emerging for the regulation of the mammalian immune system by intestinal microbes. And this interaction is extremely complex for it must provide for the activation of the immune system, yet not so strongly as to eliminate the microbes themselves – a true symbiotic relationship.

So now you have something more to think about the next time you have a tummy ache or some other intestinal malady: how it may, or may not, relate to something you ate or to the specific microbes already present there.

Richard A. “Dick” Ortez earned a doctorate degree from Creighton University in microbiology. During the past 40 years, he has taught elements of food science at the university and medical school levels, operated a café, and run a truck farm and food processing business. He writes the Seed to Table column at his farm near Glencoe and welcomes questions, comments and suggestions sent to He can also be reached at 405-338-5747.