Very, very few things make me gag, but my four year old OTTB going to town on her pasture mate's fresh manure pile is definitely one of them. I'm gagging now just thinking about it!
The consumption of feces in any species is called coprophagia- it's a fancy word for GROSS. Loads of species do it from dogs and horses, to dung beetles and monkeys. As a common animal behavior, it's believed to have the evolutionary advantage of repopulating the digestive microbiome. Basically, it's hypothesized to be the original "digestive aid" before yeast cultures were bred specifically for their digestive and immune boosting effects.
Yes, even humans have harvested the power of poop. Hasn't everyone heard of fecal transplants- also nicely named micriobiotherapy? The website for Creative BioMart® Microbe claims that this therapy has the potential to aid in a surprising array of diseases. From the Fecal Microbiota Transplantation Service website, we learn many possible advantages of our gut microbiomes for others.
"FMT [Fecal Microbiota Transplant] is a hot research field of biotherapy in recent years, and is used for the treatment researches of gastrointestinal diseases such as inflammatory bowel disease, autoimmune enteropathy, and irritable bowel syndrome, clostridium difficile enteritis, etc. At the same time, it is also a new therapeutic research direction for diseases such as Parkinson's disease, chronic fatigue syndrome, multiple sclerosis, obesity, metabolic syndrome and major depression." - https://microbe.creativebiomart.net/
Back to coprophagy in horses. Why do horses consume other's manure? How common is it? Is it a symptom of nutritional deficiency or boredom or something else? Though evidence is weak, it seems possible that deficiencies in available fiber, quality protein, and trace elements may play a role. Przewalski's horses in captivity and exhibiting several negative behaviors showed decreased coprophagy when fed hay ad libitum (Boyd, 1991). In an Italian study (Bergero et al., 2000), researchers found 16 out of 40 horses exhibiting copophragy in one sport horse stable. These 16 horses were divided into different treatment groups and fed diets that varied in vitamins and trace minerals. Their results indicate a positive relationship between coprophagy and B vitamins, folacin and Vitamin C. However, they note that other factors likely played a role that were not directly related to feeding.
The most interesting study that I found compared fecal samples of neonatal foals to their dams over the first four days of life. The researchers wanted to know how similar or dissimilar the fecal microbiota were to determine if coprophagy aids in the inoculation of the young foal's digestive system. Believe it or not, the researchers concluded that coprophagy was NOT necessary for the fecal micriobiota to be similar between mares and foals (Strasinger et al., 2013)! That would have been too easy, I suppose. Something else is going on with coprophagy that we have yet to discover.
Coprophragy can generally be categorized as an unwanted equine behavior, but is it really? Does it land in the same category as cribbing and pacing, or is it more natural than that? If we must categorize is so negatively, how have we adapted or changed those other vices?
I found several peer-reviewed articles since 2010 that attempt to address negative equine behaviors of all kinds. There is a very thorough study, published in the Journal of Veterinary Behavior and available on Google Scholar [CLICK HERE FOR LINK] in full text, that reviews a range of oral and locomotory stereotypes from wood chewing, wind sucking and cribbing to weaving and pacing. From this article, my only conclusion was that theories about stable vices in horses are still just that- theories (Sarrafchi A., H.J. Blokhuis, 2013). An article by Hathersall and Casey (2011) saw these stereotypic behaviors as malleable and encourages horse owners/handlers to be curious when determining the underlying cause of the behavior. As with ALL negative equine behavior, I believe that the best approach is to consider the entirety of your horse's daily stressors and start addressing as many as you can- yes even the stress that we cause as owners/handlers.
All things considered, I am still very cautious to make any conclusions about coprophagy. Because of this, I am extremely suspicious of supplement companies that claim they can halt any negative stereotypic behaviors with their products. The nutritional considerations mentioned in research are really just the basic nutritional requirements that we address in any good nutrition plan; forage first decisions, maximizing fiber/minimizing starch, ensuring good protein quality, and exceeding vitamin and trace mineral needs. These considerations are not special to any stable vice. The management considerations recommended are EXACTLY the same considerations we make for any well kept horse; minimizing stressors wherever possible, increasing movement and socialization, and enriching their environment. It's just plain good basics! As for me, I'm going to monitor my mare's coprophagy, but not stress unnecessarily about it. I will look away, but I will not change her diet.
Peer Reviewed Evidence
Bergero, D., M. Tarantola, B. Bassano. 2000. Feeding strategy for coprophagy events in a sport horses stable. O&DV Obiettivi e Documenti Veterinari (Italy). 21(2):31-35. ISSN : 0392-1913.
Boyd, L. E. 1991. The behaviour of Przewalski's horses and its importance to their management. Applied Animal Behaviour Science. 29(1–4):301-318. ISSN 0168-1591.
Hothersall, B. and R. Casey. 2011. Undesired behaviour in horses: A review of their development, prevention, management and association with welfare. Equine Veterinary Journal. Extracted from https://aaep.org/sites/default/files/issues/eve-24-9-479-485.pdf.
Sarrafchi A., H.J. Blokhuis, 2013. Equine stereotypic behaviors: Causation, occurrence, and prevention. Journal of Veterinary Behavior 8 (2013) 386-394.
Strasinger, L.A., A.L. Fowler, S. Hayes, G.L. Gellin, M.D. Flythe, and L.M. Lawrence. 2013. The relationship of coprophagy to fecal micriobial species richness in foals. Journal of Equine Veterinary Science. 33(5): 345.