Denele Wet Chemistry and NIR Feed Testing

Forage grass and corn silage are important components of animal feeds. Knowing all the major components and characteristics offers distinct advantages to optimize feeding.  There are two ways that forages are analyzed for nutrient content: wet chemistry and NIR. 

Wet chemistry uses established laboratory tests to quantify protein, fiber, fat, and  minerals. The minerals are smaller, thus more difficult to measure with  the NIR.  Wet chemistry should be used if precise levels are needed.

 NIR (Near Infrared Reflectance spectroscopy) has been perfected to  quickly, economically, and accurately measure nutrient content without  destroying the sample. Also, NIR technology uses light reflectance and works best  with large compounds such as those that compose protein and fiber.  The NIR  instrument must be calibrated to wet chemistry, which is the standard. Most  typical forages can be analyzed with NIR, but unique forages may not be  appropriately analyzed because no calibration set is available to standardize the  equipment. Also, total mixed rations are sometimes difficult with NIR because the composition of the mix can vary greatly from farm to farm.

When a sample is received at Denele, a portion of it is weighed and dried in an oven to eliminate the moisture. It is then re-weighed and the dry matter content is determined. The dried sample is then ground for analysis. A portion of the sample is weighed into a tube for a Kjeldahl or nitrogen determination. There are other methods of nitrogen determination, but this is the most common. The sample is digested with acid and then distilled with a base solution to convert nitrogen to ammonia, a form that can be trapped and analyzed. Nitrogen is converted to crude protein by multiplying by 6.25, due to the fact protein is 16 percent nitrogen (100/16=6.25). Crude protein measures all nitrogenous compounds present in the sample and does not distinguish true protein from nonprotein nitrogen. This is fine for ruminants (cattle, goats, and sheep), but can be a concern for chickens and swine because they cannot utilize nonprotein nitrogen.

Forage testing labs typically run two types of fiber determinations. One uses an acid detergent solution to digest the dried-feed sample, and the other uses a neutral detergent solution. The digested solution is filtered and the residue on the filter is the fiber. These fibers are termed acid detergent fiber (ADF) and neutral detergent fiber (NDF). NDF is larger than ADF in plants and is considered to be the cell wall component. NDF is used to predict intake while ADF is used to predict digestibility. Both can be used to estimate energy.

When expressing concentration of nutrients, it is necessary to define whether the results are expressed on an actual (“as is”) or dry-matter basis. Nutrient concentrations expressed on an “as is” basis are less than when expressed on dry matter. In species such as cattle and horses that eat wet feed, rations generally are calculated on a dry basis. Pigs and chickens eat feeds that are dry and have approximately the same dry matter (88 percent to 92 percent) and will sometimes use the “as is” nutrient concentration. The feed industry uses the “as is” basis to express nutrient concentration on feed tags. Therefore, it is important to know what basis nutrients are expressed before it is possible to use the results. Crude protein, fiber, fat, and macrominerals (calcium, phosphorus, etc.) are usually expressed as %. However, microminerals (zinc, cobalt, etc.) are usually expressed in parts per million (ppm). Energy will be as % TDN or kilocalories or megacalories per pound. Vitamins are expressed as international units of activity per pound. Therefore, it depends on the nutrient type as to what units will be used.