One feature of alfalfa researchers have been studying for years is condensed tannins. Tannins are a set of compounds found naturally in the seed coat of alfalfa. Researchers have been working for several years to find a way to produce tannins in the leaves and stems of the alfalfa plant instead of just the seed coat.
Peter Robinson, dairy nutrition extension specialist with the University of California, says tannins research had its first heyday back in the ’60s and ’70s in places like Canada, the United Kingdom, South Africa and Australia, where they worked to develop the amount of tannins in forages in hopes of increasing grazing efficacy.
In the last 10 to 20 years, tannins research has made a comeback. One of the leading companies in the field is Forage Genetics International (FGI), based out of Minneapolis, Minnesota.
Stephen Temple, director of biotechnology at FGI, says the benefits of increased tannins in alfalfa can be narrowed down to two points: improvement in bypass protein efficiency and increasing the ability to graze alfalfa in the field. “Our immediate target with this trait is the bypass protein,” Temple says.
“The grazing and bloat part is secondary because it’s not really a current agronomic practice in the U.S. for large dairies.”
FGI research
Temple says FGI has been experimenting with tannins since the early 2000s. Although no one has found a way to increase the amount of tannins in the alfalfa plant itself, they have learned a lot more about how tannins work in the dairy diet.
He says FGI and research partners are in the early stages of developing condensed tannins in alfalfa but have a long way to go before they will be ready to release a commercial product. “If success is a commercial product, then nobody has succeeded,” he says. “But we have learned a lot about the pathways and how the synthesis occurs and things associated with that. That’s historically where the interest is.”
Temple says it comes down to researchers figuring out how to engineer pathways to help spread the tannins compound throughout the plant. “It’s in the seed coat, and what that tells me is: The genes are all there in alfalfa,” Temple says. He says while the genes are not being expressed, they are there in the plant, which is half the battle.
“From a standpoint of an engineering strategy, the fact the genes are in alfalfa is a whole lot better for me than the genes not being there at all; then we’d have to engineer the whole pathway and get it regulated correctly.”
Temple compares FGI’s work on an increased tannins model of alfalfa to the Roundup Ready alfalfa seed they released a few years ago. He says they developed the Roundup Ready trait by adding a synthetic version of a single gene already in the plant.
By contrast, to produce tannins into the rest of the plant, they have to regulate an entire suite of genes. “It’s a very complicated pathway, and to be completely honest, there are still parts of the pathway we don’t understand, and we don’t know all the steps, so we are not able to regulate them,” he says. “It’s a pathway engineering strategy as opposed to a single step, while things like Bt and herbicide tolerance are typically single-step trans-genetics.”
Tannin’s effect on bypass protein
The big draw of increased tannins in alfalfa is what they can do to aid bypass protein efficiency. “When a dairy cow is feeding, it’s got a high-forages, high-alfalfa diet, and there’s a lot more protein than the animal can typically use, and a lot of that protein is lost,” Temple says. “If it’s a dairy cow, that means it’s not assimilated into milk or, if it’s a beef cow, it’s not assimilated into biomass in the animal. A lot of that protein is broken down in the rumen and not assimilated and lost out the back of the animal, so it’s not utilized very efficiently.”
Robinson says this is where tannins come into play. “Tannins can interact with proteins, not just in the alfalfa but from other feeds as well, so in the bunk line they’re non-reactive, but the moment they get into the watery situation in the rumen, then they can be solubilized and react with other proteins, so they would increase the rumen undegradability of proteins in the entire diet by interacting with soluble proteins coming from anything else.”
In the relatively neutral pH of the rumen, the tannins temporarily bond with the broken-down protein, helping it pass into the small intestine. “Think of the protein being coated in this polymer of tannins. It’s a little more complicated than that, but it’s a good visual,” Temple says. “In the lower pH of the intestine, this association will break down, so then the proteins are released and the animal can digest that material, and it will be used for either biomass production or, for a dairy cow, milk production.”
Grazing with increased tannins
The other benefit of tannins Temple says is likely but not proven is the development of a variety of alfalfa that could be grazed in the field rather than harvested for hay. “This is a little more theoretical,” he says. “We do know if ruminants graze where there are tannin-containing legumes, you see lower levels of pasture bloat.
It’s been a tantalizing trait for the alfalfa researchers for many years, and a number of groups have spent a lot of money and a lot of time, and there’s been a lot of really good research by some really top-notch people over the years aimed at doing that,” Temple says.
Temple believes the grazing benefits of increased tannins in alfalfa would be aimed more toward Argentina and Central and South America, where alfalfa is generally grazed but, if it was made possible, could likely change in the U.S. as well. “If you could graze animals, maybe the amount of grazing would go up,” he says.
“We don’t know the answers to that, so if we get to the point where we have alfalfa that has all the things we want, we would move to do those types of studies fairly early on.”
Temple says if increased-tannins alfalfa becomes a real possibility, palatability could become a problem. “The evidence on this one is a little hard to prove because you can’t exactly ask a dairy cow what her food tastes like, but we do know if you eat things that have tannins in them, they do have a bitter taste, so we assume if you got the levels high enough, there would probably be a palatability problem, so you would need to establish what that is and avoid going beyond those levels,” he says. He thinks those levels would most likely be well beyond what farmers would feed out anyway.
Future of tannins
Robinson says he is unsure what would happen if the amount of tannins available in alfalfa hay in dairy rations were increased or how it could change how dairy rations are constructed.
“Metabolic models commonly used by consulting nutritionists don’t take into account impacts of secondhand compounds like tannins. There’s no way you can answer the tannin level of a plant or feedstuff in any metabolic model that I’m aware of. You just don’t enter it, so it doesn’t exist in terms of being a characteristic of the feed.”
Tannins research has come a long way in terms of what we know about the alfalfa plant and how its genetic pattern works. Robinson says if the research yields a high-tannins variety, the real breakthrough will be when farmers actually start using it. 
PHOTO: Cows grazing. Photo by Aubrey Fletcher.
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Carrie Veselka
- Associate Editor
- Progressive Forage
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