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CALS dairy science professor David Combs has developed a forage fiber test to identify the best feeds for cows - and milk production. Photo by Sevie Kenyon BS'80 MS'06

You might expect that the most important break-through in feeding dairy cattle in years would rate a snazzy name. Instead, you get “total tract neutral detergent fiber digestibility”—TTNDFD for short.

“Yes, I know. That’s a terrible name. But unless someone comes up with something better it’s TTNDFD,” says CALS dairy nutrition scientist David Combs.

No matter. For an idea this good, a clever name isn’t needed.

The discovery of TTNDFD, a new forage test, lays to rest a mystery that’s perplexed researchers and dairy farmers since scientific forage analysis began 40 years ago: Why cows would wolf down one finely tuned dairy ration but turn up their noses at another that, on paper, was identical?

“We couldn’t put a finger on it,” Combs says. “You’d get your forage analysis, balance the ration, and everything seemed fine. But one time the cows would eat everything up, the next time you’d get a high rate of refusal.”

That mystery cost money. When cows eat to capacity, they produce milk to capacity, and milk sold off the farm is what pays the bills. “It wasn’t so much good forage, bad forage. Those things we can detect. It was those times when everything seems fine and the cows would not eat as much as expected or not produce as well as before,” Combs says.

Cows are professional eaters and highly discerning about what gets served. They’ll eat a lot of differ- ent things but will eat a great deal more of the things they like best. What the Combs team figured out— through research that involved 20 years of reaching into the 30-gallon vats known as cow rumens—was that how much cows gobbled up and turned into milk was influenced by the rate of fiber digestion. Developing a test to account for it ushered in a new feeding system that offers several advantages.

For one, the new forage fiber test lets farmers see the differences in the feeds they have on hand. For another, it helps them grow and buy the types of feeds most favored by cows. For yet another, plant breeders can use the test to create the type of crops cows want the most. And most important, the test can help milk producers make more money.

“How fiber is digested can easily make five to six pounds per day difference in milk production in a dairy cow,” Combs says.

There could also be some positive ripple effects. As people applied the test to all kinds of forage, they discovered that grass is something of a magic missing ingredient in the daily dairy diet. The right kind of grass is really good for cows, and the test can help farmers select the right grasses to grow.

Reintroducing grass to dairy diets on a large scale could be great for the landscape. Grass soaks up carbon and nutrients, holds soil in place, covers otherwise bare ground during the winter, and can help absorb manure applications.

The test also opens opportunities for entrepre- neurs. When Rock River Labs in Watertown hired John Goeser BS’04 MS’06 PhD’08, who’d earned a doctorate under Combs, it became the first lab in the world to offer this new analysis to the dairy community.

“It’s started a little slow. But it went from no tests to 5,000 tests in a season,” Combs says. Now Combs uses a large spreadsheet to review the data being generated by thousands of TTNDFD tests performed by Rock River. More labs are looking into offering TTNDFD results as part of a forage analysis package.

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