A Horse, a Human, and a Microbe walk into a Barn…..

by Kip Tulin

Note: There are quite a few 50-cent words in here which you may feel free to skip past in search of Dr. Tulin's point about feed and supplementation. Science geeks, enjoy! -MG

humans, horses, dog, and gazillions of microbes...

….and while hanging out around the treat bin, they decide to find out if they have anything at all in common. Horse and human, sure. But a microbe?? Turns out all three (human, horse, microbe) have more in common than you might think: they—and I might as well say ‘we’— all have DNA made up of the same four ‘letters’ (called nucleotides) and they all use groups of three of these letters (triplets) to code for the the same twenty ‘building blocks’ (amino acids). It is truly amazing to think that all of the immensely diverse living things on earth, whether single celled, plant, insect, or animal use the same basic code of life.


As a people doc, new to horses but very familiar with microbes, I find the links between horse and human health fascinating. While searching for more basic information on similarities in horse and human nutrition, I recently came across this extremely basic—as in, basic building blocks of life—information and was blown away by the knowledge that all living things are linked in this way. I’m going to dig a little deeper, then come back up for air and talk about connections to nutrition for you and your horse.

The details. So how is it possible for all of the wildly diverse forms of life on earth to come from just four ‘letters’ and twenty ‘building blocks’? Let’s go inside the cell and find out. The well known double helix of DNA is a very, very long spiraling chain of paired molecules called nucleotides; cytosine, adenine, thiamine, and guanine (hint: these MAY be on the quiz). These ‘letters’ form the backbone of the DNA chain and are read in groups of three, such as CCA (for the amino acid proline) or GCG (for the amino acid alanine), etc. Their order on the DNA chain dictates how the amino acids will be linked up to form whichever proteins are needed by the cell. Each cell has an elegantly intricate system to unzip the double helix, ‘read’ the DNA to make the protein chains and zip everything together again. All of life’s diversity comes from the variations in these proteins as dictated by the DNA coding.

Cool. Amazing. So what?

This mechanism has implications for the diets of horses, humans, and microbes. We all need a full set of amino acids to build cellular proteins. Depending on where you are in the tree of life you may be able to synthesize some or most of the needed amino acids. So some we can make by  ourselves, but other amino acids we have to get from other sources such as food or the bacteria in our guts.

The key point here is that if you are missing even one of the amino acids from other sources, no matter how rich your diet is in overall protein, your cell growth will be limited by that missing amino acid. It’s kind of like having enough parts to build 100 cars, but you only have 300 tires.  So you end up with 75 perfect cars and 25 that are pretty useless.

The good news for humans is that our diets are usually so varied that we get all of the amino acids we need (yes, even vegetarians). 

The news for horses is mixed:  Since our horses are limited in their ability to shop for groceries, they depend on us to balance their diet. And in our efforts to do a good job, we may over- and under-shoot their nutritional needs. For instance, if you are giving your horse a high protein supplement, you need to be sure that you are truly filling in gaps in their main feed. They may well be getting adequate protein from their feed.  And other nutrients. The question is, what is missing that needs to be supplemented? It’s tempting to buy products that promise health, but which may not actually be addressing the gap in your horse’s nutrition.

If your horse lives on hay grown at Freedom Farm, you are in luck: their hay is carefully analyzed at a certified lab every year. It’s the only way to screen for deficiencies and the only accurate gauge for formulating needed supplements. Check with Mary Gallagher for more information and in this case, if you are feeding Freedom Farm hay, you might consider getting the Farm’s customized supplement for your horse.

The bottom line: Over supplementation of amino acids, protein, vitamins, minerals, etc. is not helpful and in most cases only serves to produce very expensive urine in horses and humans. And FYI, there is no significant increase in the need for protein due to hard exercise, and in fact, over supplementation may create problems. So get the facts on your horse’s feed, and supplement from there. Balance is the key.

And as the horse reminded the human and the microbe as they chatted together, treats are always appreciated.*

Kip Tulin MD

*last sentence added by Bob, my horse buddy