Cow Pies Can Make You Smarter and Less Stressed

It seems like everyone is running around buying school supplies and books, registering for classes, and fretting about how hard it is going to be to learn another whole year’s worth of stuff. The secret to success, it turns out, may lie in cow dung.

A cow pie. Photo taken by Jeff Vanuga at
the USDA available at Wikimedia Commons.

Recent research has highlighted the important role that microbes living in animal digestive tracts have on host animals’ health and behavior. This influence of our gut microbes on our behavior is called the microbiota-gut-brain axis. Many of these microbes have long-standing populations that reproduce and spend their whole lives in our guts. Because our digestive tracts do not have much oxygen, these species are anaerobic (do not require oxygen to live). However, our gut communities also have more transient aerobic members (species that do require oxygen to live) that come in when they are ingested and die or leave with the droppings. One of these transient aerobic intestinal citizens is Mycobacterium vaccae (or M. vaccae for short), an aerobic bacterium that naturally lives in soil, water, and yes, cow dung.

When mice are injected with heat-killed M. vaccae, they develop an immune response that activates their brain serotonin system and reduces signs of stress. Serotonin is a neurotransmitter that is found in the brain and is involved in regulating alertness, mood, learning and memory. In fact, many antidepressant drugs work by increasing the amount of available serotonin in the brain. Interestingly, serotonin is also found in the digestive system, where it plays a role in digestive health. Since M. vaccae can increase serotonin function, and serotonin reduces anxiety and improves learning, researchers Dorothy Matthews and Susan Jenks at The Sage Colleges in New York set out to test whether eating live M. vaccae could reduce anxiety and improve learning in mice.

A drawing of the mouse maze used by Dorothy and Susan.
This image is from their 2013 Behavioural Processes paper.

The researchers developed a Plexiglas mouse-maze with three difficulty levels, where each increase in difficulty was marked by more turns and a longer path. They encouraged the mice to run the maze by placing a tasty treat (a square of peanut butter on Wonder Bread™) at the end of the maze. Half of the mice were given live M. vaccae on the peanut butter and bread treat three weeks and one week before running the maze, and then again on each treat at the end of each maze run. The other half were given peanut butter and bread without the bacterial additive. The mice then ran the maze roughly every other day: four times at level 1, four times at level 2 and four times at level 3. Each maze run was video recorded and the researchers later watched the videos to count stress-related behaviors.

The mice that ingested M. vaccae on their peanut butter sandwiches completed the maze twice as fast as those that ate plain peanut butter sandwiches. They also had fewer stress-related behaviors, particularly at the first difficulty level of the maze when everything was new and scary. In general, the fewer stress behaviors a mouse did, the faster its maze-running time was. The mice that ate the M. vaccae also tended to make fewer mistakes.

The researchers then wanted to know how long the effects of M. vaccae lasted. They continued to test the mice in the same maze, again with four runs at level 1, four runs at level 2 and four runs at level 3, but for these maze runs no one was given the M. vaccae. The mice that had previously eaten the M. vaccae continued to complete the maze faster and with fewer mistakes and to show fewer stress-related behaviors for about the first week before the M. vaccae effects wore off.

What does this all mean? It means eating dirt isn’t all bad (although I don't recommend eating cow poop). Letting yourself get a bit dirty and ingesting some of nature's microbes could even help you learn better, remember more, and stay calm - especially in new situations. Just something to think about as the school year gets started.

Want to know more? Check these out:

1. Matthews, D., & Jenks, S. (2013). Ingestion of Mycobacterium vaccae decreases anxiety-related behavior and improves learning in mice Behavioural Processes, 96, 27-35 DOI: 10.1016/j.beproc.2013.02.007

2. Lowry, C., Hollis, J., de Vries, A., Pan, B., Brunet, L., Hunt, J., Paton, J., van Kampen, E., Knight, D., Evans, A., Rook, G., & Lightman, S. (2007). Identification of an immune-responsive mesolimbocortical serotonergic system: Potential role in regulation of emotional behavior Neuroscience, 146 (2), 756-772 DOI: 10.1016/j.neuroscience.2007.01.067