Test legume-grass silage for bypass protein

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The preferences of Goldilocks, from the children's story including three bears, can help you remember the primary rule of feeding bypass protein. Just as Goldilocks searched to find accommodations that were "just right," if protein supplementation isn't "just right" in post-rumen digestion, your cows' production won't improve.

"The challenge when feeding bypass protein comes in not only meeting the amino acid requirement of the small intestine, but also in not exceeding it," says Charlie Sniffen, president of the Miner Institute, a dairy research facility in Chazy, N.Y. Feeding too much bypass protein or too little can result in poor production response.

Accurately determining the amount of protein that would, in fact, bypass the rumen has been an obstacle when implementing bypass feeding in dairy nutrition. While the National Research Council (NRC) provides "book" values for the bypass protein of all feedstuffs, lackluster performance in the field indicates that some sort of variance is occurring - especially among forages.

However, research by the University of Wisconsin, reported in the April 1999 Journal of Dairy Science, shows that Near-Infrared Reflectance Spectroscopy (NIRS) analysis can evaluate the bypass protein in grass and legume silage more accurately than NRC values. That, in turn, can help you get the most out of bypass feeding.

Perfect application
With much debate going on about the value of NIRS technology when compared to wet chemistry analysis, many nutritionists, feed representatives and dairy producers may be skeptical of the NIRS technology's ability to accurately detect bypass protein levels.

NIRS analysis subjects the forage sample to near-infrared light waves and measures the absorption of those waves. The chemical components of the sample determine the exact wavelength absorbed and the strength of absorption. This absorption is then related to quality factors, such as the level of protein or fiber in the sample.

For example, the new bypass protein test was calibrated with 121 forage samples placed inside cannulated cows to determine how much protein in the sample escaped the rumen. The samples used to calibrate the NIRS analysis were from various forage species, with a wide range of maturity and moisture content to represent a wide range of protein degradation.

According to Pat Hoffman, dairy scientist at the University of Wisconsin's experiment station in Marshfield, Wis., who developed the test, NIRS has certain advantages and disadvantages. For example, NIRS has a difficult time evaluating mineral fractions of feeds. However, NIRS does a good job reading protein and fiber fractions, therefore evaluating grass and legume silage is "a technically beautiful application" of the technology, Hoffman says. "The NIRS sees the molecular bonds associated with silage protein," he adds. And, because degradable protein and bypass protein have different molecular structures, NIRS can see and measure the different protein fractions.

Turning art into science
For years, nutritionists have been calculating the amount of bypass protein in rations with finesse because no test provided accurate bypass protein levels. By using NRC values, along with field experience, some nutritionists have been able to estimate the protein available for the small intestine reasonably well.

However, the NIRS bypass protein test has proven to be a more accurate tool. Last summer, 300 samples of legume-grass silages were supplied by Wisconsin nutritionists to the Marshfield Soil and Forage Analysis Laboratory in Marshfield, Wis. The NIRS bypass protein test predicted the average bypass protein content of the silages to be 21.8 percent of crude protein fed. That's near the NRC's book value for bypass protein of between 20 percent to 25 percent of the crude protein. However, the NIRS test also revealed a wide range of bypass protein among the individual samples, ranging from 14.2 percent to 36.5 percent of the crude protein. Therefore, you can be deceived if you simply go with book values.

With more precise bypass protein readings, nutritionists can make needed changes to the ration.

Of the 53 nutritionists surveyed in last summer's experiment at Marshfield, 27.5 percent increased the herd's bypass supplementation. And, 17 percent were able to decrease the cost of bypass protein supplementation by getting a more accurate reading on the protein fraction. The survey also showed that milk production increased in 12 percent of the herds, and no herds saw a production decrease.

Producers who feed rations formulated to take advantage of bypass protein should consider using this new test. At a cost of approximately $10 per test, it's a small investment to make for something that can help you get the most out of the dollars you spend on bypass protein.


An additional troubleshooting tool

Sometimes, nutritional problems don't reach out and grab your herd. Rather, they nag at it. For example, milk protein goes from 3.2 percent to 3.1 percent and you can't figure out why. Or, the high group is eating 3 pounds less for an undetermined reason. According to Pat Hoffman, dairy scientist at the University of Wisconsin, under-feeding or over-supplementing bypass protein can result in the following problems:


  • Decreased milk protein.
  • Decreased intakes.
  • Weight loss.
  • Poor peak milk yield.
  • Lack of persistence.


The NIRS bypass protein test can be used as a troubleshooting tool in these situations. "The test helps you better understand what's happening with your protein fractions," says Spence Driver, dairy technical services manager for Vita-Plus Feeds.

For example, if the bypass protein test of a grass-legume silage shows an abnormal bypass level of 35 percent of the crude protein, the soluble protein (instantaneously degraded in the rumen) level will probably be low, which indicates the herd needs degradable protein supplementation and not bypass protein supplementation, says Hoffman.

If you are interested in using the grass-legume silage bypass protein test, it is available at the following labs at a cost ranging between $8 to $16:

  • Marshfield Soil and Forage Analysis Laboratory, Marshfield, Wis. (715) 387-2523
  • Dairyland Laboratories, Arcadia, Wis. (608) 323-2123
  • Ag Source Soil and Forage Laboratory, Bonduel, Wis. (715) 758-2178
  • Stearns Central Laboratory, Sauk Centre, Minn. (320) 352-2028
  • Rock River Laboratory, Watertown, Wis. (414) 261-0446


If your lab is not listed, ask the officials there about adapting this new technology.


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