The result: A grass with exciting implications for high-fertility forages and high-producing animals. A sweet grass; a sweet story.
Wales is a beautiful place with a mild climate ideal for perennial ryegrass (Lolium perenne). Although perennial ryegrass is already valued worldwide for its high digestibility and palatability, scientists at IGER – the Welsh Institute of Grassland and Environmental Research – still wanted to improve it.
They noted that perennial ryegrass is rather adept at making sugars, which helps explain why livestock like it so much. So they bred some genetic lines to increase the level of soluble sugars in the leaves.
After years of careful selection, they recently released some ryegrasses that indeed contain higher sugar levels than other grasses. These cultivars have names beginning with “Aber,” such as AberDart, AberAvon and AberEcho.
Wales is also renowned for its tongue-twisting place names, like the small town with one of the longest names in the world, which translates as, “The church of St. Mary in the hollow of white hazel trees near the rapid whirlpool of Llantysilio of the red cave.” Really.
Check it out on Wikipedia. It’s a good thing that Welsh scientists don’t name their grass cultivars after towns.
But for millions of years, perennial ryegrass existed quite comfortably without ultra-high sugar levels. Why all the fuss? Now let’s get into the nutrition side of it.
Modern forage analysis divides forage dry matter into two major fractions: cell walls (which contain nearly all the fiber and are represented by the neutral detergent fiber value in a test report), and non-cell walls, which contain the contents of cells, identified by subtracting the neutral detergent fiber value from 100.
For example, if the dry matter of a grass contains 58 percent neutral detergent fiber, then its cell contents would be 42 percent.
The cell contents include things like sugars, starches, soluble proteins, non-protein nitrogen, organic acids, lipids (fats) and a very digestible fiber called pectin.
The sugars are small water-soluble compounds which represent some of the more tasty substances in the forage. They include familiar carbohydrates, such as glucose, fructose and sucrose. In contrast, starches are huge storage compounds that are actually polymers of simple sugars, and they are far less soluble than simple sugars.
Nutritionists often lump sugars and starches together under the banner of non-structural carbohydrates. Although the jargon may be a bit confusing, it’s the sugars we are now interested in.
When a leaf cell captures sunlight for photosynthesis, the main product of this reaction is the simple sugar: glucose. But glucose is really just a first step, a metabolic building block. Glucose molecules are quickly swept into a multitude of metabolic reactions to manufacture thousands of other plant compounds, like starch and proteins.
But those Welsh researchers successfully bred plants that utilized sugars at a slower rate, thus causing a buildup of water-soluble sugars in the leaves. The result: high-sugar grasses.
A real advantage of these plants occurs when they receive high rates of nitrogen fertilizer and are then grazed by high-producing animals. Here’s what happens: High levels of nitrogen fertilization can result in high nitrogen levels in forages, particularly during their fast-growing vegetative period.
Over the years, we’ve tested young grasses that contained crude protein levels greater than 28 percent, even as high as 37 percent.
In reality, those high values aren’t all true protein. Remember, laboratories don’t analyze for true protein, they actually analyze for nitrogen. Then they multiply that nitrogen value by 6.25 to get the reported level of crude protein. Therefore, a crude protein value of, say, 28 percent means the plant contains 4.48 percent nitrogen (28 = 4.48 x 6.25).
Actually, plants don’t really contain that much true protein in their cells. Some of this nitrogen occurs as non-protein nitrogen, such as nitrates, individual amino acids and other nitrogenous compounds.
When animals graze forages, all that nitrogen enters the rumen. Rumen bacteria and protozoa use as much nitrogen as they can, metabolizing it into proteins for their own bodies. But they can’t use all the nitrogen, especially if forages contain so much.
Excess nitrogen in the rumen is quickly converted into ammonia, which is then absorbed across the gut wall into the blood, transported to the liver and converted into urea, which is then excreted in the urine.
If you’ve followed me, you’ll recognize that we’ve just come full circle. Nitrogen begins in the soil, moves through plant roots into the leaves, is grazed by animals, moves into the rumen, then the liver, then the urine and finally is excreted back onto the ground.
A convoluted, nutritionally inefficient, wasteful cycle (and expensive, too) – nitrogen moving from soil to plant to animal and back to soil again without creating useful animal product.
But here is where high-sugar grasses can really shine. Like many things in life, it’s a matter of timing. When animals consume high-nitrogen forages, rumen bugs utilize the nitrogen by combining it with carbohydrates to form their own amino acids and proteins.
However, those carbohydrates must be available to the rumen bugs at the same time the nitrogen is present in the rumen. If the rumen contains more nitrogen than available carbohydrates, the extra nitrogen is lost to ammonia. Timing is essential. The availability of different nutrients must be in sync.
For rumen bugs to capture some of this extra nitrogen, they need carbohydrates available at the right time. And since non-protein nitrogen converts into ammonia very quickly, those carbohydrates must be available just as quickly. Unfortunately, starch becomes available too slowly in the rumen for this process.
But soluble sugars will do the trick, since they are available to the rumen bugs while the non-protein nitrogen is still present in the rumen.
In essence, high-sugar grasses provide extra sugars to the microbes at the right time so the amounts of nitrogen and available carbohydrates are in better sync. The rumen microbes can now capture a greater percentage of the plant nitrogen.
They can create more microbial bodies which, in turn, provide more nutrients to the animal. And less plant nitrogen is lost to ammonia.
There is a proviso, however. This situation nutritionally benefits animals that can utilize the extra nutrition, like high-producing dairy cows on pasture, or ewes or does raising twins or triplets, or youngstock striving for the highest rates of gain.
Livestock with lower nutritional requirements don’t need the extra nutrients and will excrete the extra nitrogen anyway.
There are other aspects to high-sugar grasses that we can cover, like palatability, intake, the making of silage and hay, and what these grasses can mean for horses. But let’s have patience – we’ll cover these at a different time.
Meanwhile, find some of those high-sugar grass blades and try chewing them. Even if you don’t personally need that extra nutrition, those leaves are really sweet. 
PHOTO: In essence, high-sugar grasses provide extra sugars to the microbes at the right time so the amounts of nitrogen and available carbohydrates are in better sync. The rumen microbes can now capture a greater percentage of the plant nitrogen. Photo by Lynn Jaynes.
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Woody Lane, Ph.D.
- Certified Forage and Grassland Professional
- AFGC
- Email Woody Lane, Ph.D.
