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All the Sad Horses

What race horses taught me about the gut-brain connection.

A horse is dangerous at both ends and uncomfortable in the middle. —Ian Fleming

Scott Anderson
Source: Scott Anderson

Rodents are the go-to research animals, and for good reasons. They breed quickly, they're easy to work with, and cheap to maintain.

Only an idiot would choose to do research on horses, which are large, expensive animals whose owners are not keen on people poking at them. But I like horses, so I jumped at the chance to do research on the most expensive equine divas of all — race horses.

In 2004, I became the head of research and development for Freedom Health, LLC., a company that makes supplements for humans and animals – including horses. I worked with Frank Pellegrini, a brilliant and inquisitive horse vet.

Frank had been obsessing for years about "poor-doers." These horses are listless and display distinctive behaviors like chewing their stables and nosing their abdomen. As scientists, we are not supposed to anthropomorphize, but these horses seemed sad.

Frank noticed a low level of anemia in these poor-doers. To find possible blood-losing lesions, he scoped their stomachs. He often saw ulcers, but not always. He thought other ulcers might be lurking in the colon, but you can't do a colonoscopy on a horse – by the time you evacuate its gut for scoping, the horse will be half-dead.

Still, Frank had to know what was going on. He dreaded it, but he knew the answers could only be found at an abattoir. When people get tired of their horses, they often end up at an abattoir. There are more abandoned horses than you want to think about. But here Frank could examine their entire digestive tract. For a horse-lover like Frank, it was sad and draining work.

Frank did 180 necropsies on horses in Texas, and found that 60% had colonic ulcers, many quite serious. It was a revelation, and not a happy one. Frank and I created a fecal antibody test that could detect blood proteins that were likely colonic in origin. We calibrated it with more necropsies. Using this test, we could finally visualize the existence of colonic ulcers. A positive result generally correlated with a crappy attitude and poor performance.

Something in their gut seemed to be causing these horses distress. My own gut was telling me it was bacteria. We theorized that unnatural high-energy racing diets pushed too much starch through the gut, causing a bloom of acid-producing bacteria. The lowered pH disrupted the horse's microbiota and eroded the gut lining. That "leaky gut" then led to systemic inflammation and – somehow – poor-doers.


Fast-forward a decade: I'm working as an independent consultant and underpaid science writer. The gut-brain axis is trending, and with my unique horsey background, it has great appeal to me. One day in my research, I came across the term psychobiotic . In 2013, psychiatrist Ted Dinan coined the term psychobiotic to mean "a live organism that, when ingested in adequate amounts, produces a health benefit in patients suffering from psychiatric illness." [1]

Scott Anderson
John F. Cryan and Ted Dinan
Source: Scott Anderson

Could psychobiotics help sad horses? I got in touch with Dr. Dinan and his research partner at the University College Cork, John Cryan. It turned out that professor Cryan had read some of my science articles. Fortunately, he liked them. John and Ted are alarmingly energetic and prolific researchers. They and their colleagues are at the forefront of gut-brain research. I wanted to tell their story. After some discussion, I proposed we write a book on psychobiotics. I was honored and humbled when they accepted. We signed a deal with National Geographic in 2015 and the book launched as The Psychobiotic Revolution in late 2017.

The connection between gut bacteria and mood is unexpected and wonderful, but why did it take so long for researchers to discover psychobiotics? Because, just like equine colonic ulcers, they were hard to see. Until a few years ago, the standard technique to identify bacteria was to culture them in a Petri dish. But most intestinal bacteria couldn’t be cultured, so all we got was a tiny peek at the bustling microbial metropolis that occupies the gut.

The advent of DNA-sequencing machines changed everything. Suddenly scientists could classify thousands of microbes in one go, down to the genus level. Similar microbes were found in all animals tested, including people. That brought us to the sobering realization that humans are not all human: our guts are stuffed with a couple of pounds of microbes called the microbiota, and it's essential to our health. As well as protecting us from pathogens, our microbiota produces fatty acids, hormones, cytokines and neurotransmitters. Through these various chemical pathways, microbes affect our mood.

As the incidence of depression continues to climb (according to the WHO, depression is now the number one cause of disability), we need more than ever to fill in the details of how the gut and brain are connected. In upcoming posts, I will highlight the latest amazing breakthroughs about the gut-brain axis — for both people and horses. Prepare to have your mind blown and your mood lifted.


[1] Dinan T.G., Stanton C., Cryan J.F. Psychobiotics: A Novel Class of Psychotropic. Biological Psychiatry, November 15, 2013 Vol 74,10:720–726