Low-quality feeds such as straw cool off hot rations because of what they contain — digestible and indigestible fiber, say two dairy nutrition experts.

But it's essential to have the right amount of indigestible fiber, or lignin, to improve rumen function and slow rate of passage, says Mike Hutjens, an extension dairy nutritionist with the University of Illinois.

“It looks like rations that contain less than 3% lignin do not work very well,” adds David Byers, a Galax, VA, veterinarian and dairy production consultant. “And we particularly see this in those high-quality, low-NDF, highly digestible corn silages.”

Straw wouldn't be Byers' choice, however. “There are better sources to use for lignin. For example, whole cottonseed.”

Dairy rations should center around carbohydrates, including non-fibrous starches and sugars and the fiber carbohydrates — hemicellulose, cellulose and lignin, Byers says. A balanced ration should be 32-34% NDF. Hemicellulose and cellulose make up the bulk of that figure, but lignin should account for at least three percentage points. And Byers would like to see it at four.

“My own personal experience was, when I had less than 3% lignin, I didn't get as much milk. And my components were less — less milkfat and less milk protein,” Byers says. “Only when we got lignin into the neighborhood of 3-4% would it get to the performance that we were accustomed to.”

But why is lignin important?

“We're seeing,” says Hutjens, “that we may need a certain amount of feed that slows down the rate of passage and improves rumen function and digestion. In the long run, it makes the cow function more properly.

“Lignin helps maintain rumen mat and an optimal rate of passage, allowing for improved feed efficiency. And it has to be the correct amount, because if it's too high, it really slows things down,” he says.

Particle size is important, too. A certain percent of a total mixed ration (TMR) should be ¾-2” long so it stimulates cud chewing and cows can't sort it. If a Penn State Forage Particle Separator test shows 10% of the TMR in the top box and 40% in the middle, the ration is providing enough effective fiber.

Dairy producers who want to know how much lignin their rations hold can have it measured with a wet-chemistry test.

At this point, say Hutjens and Byers, they have no scientific research to back up their supposition on lignin levels. So Hutjens would like nutritionists' help.

“It would be interesting for me to look at high-producing herds to see what level lignin they have in their rations,” he says.

To contact Hutjens, call 217-333-2928 or email him at: hutjensm@uiuc.edu.