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Forage analysis: An invaluable tool

John Hibma for Progressive Forage Published on 27 December 2018
Foarage analysis

The foundation of all ruminant diets is forage. The ruminant digestive system cannot function correctly without forage.

In order for beef cows to maximize daily gains, for dairy cows to maximize milk production and all ruminants to remain healthy and productive, they must consume high-quality forages.

Most of us who have been around the animal feed industry and forage production long enough can tell the difference between a good bale of hay compared to a poor bale of hay or a good pile of corn silage compared to a bad pile of corn silage. Often, just the sight, smell and texture of hay, haylage or corn silage will guide us the majority of the way toward the decision of picking a feed for a cow or heifer diet.

But who among us hasn’t been confounded by the subtle differences between two hay crops, hay that looks the same but doesn’t milk the same? Why is it one year’s corn silage milks better than another year’s silage? Isn’t all fiber the same? For the answer, we must turn to the modern, computerized forage-testing laboratory that can tell us amazing things about forage while redefining forage quality along the way.

The major components of forage can generally be separated into three groups: protein, carbohydrates and minerals. The portion of feed we call fiber is actually part of the carbohydrate fraction. All three groups have nutritional significance in ruminant diets. A cow’s rumen processes the carbohydrate and fiber fractions at different rates.

Microbes in the rumen utilize some of those fractions quickly, while others are degraded more slowly and still others are hardly touched in the rumen or intestines and are excreted. Proteins are handled differently, as well, based upon their amino acid profiles.

Laboratory assays for crude protein and fat were developed many years ago. The calculation for total digestible nutrients (TDN) remained the gold standard for determining energy levels in feeds for many decades. Fifty years ago, all a farmer needed to know was the moisture, crude protein (CP) and TDN of a forage to make an intelligent decision about the quality.

Today, however, with the help of modern laboratory analyses of the different nutrient fractions, diet formulations have become more sophisticated, allowing dairy nutritionists to meet a ruminant’s nutritional needs on a variety of production levels, reducing the release of unused nutrients into the environment.

Ruminant scientists have determined that within the carbohydrate portion of forages, there are fractions with varying degrees of digestibility, from fully digestible simple sugars to nearly indigestible lignin. They have developed laboratory assays to determine those fiber fractions – acid detergent fiber (ADF) and neutral detergent fiber (NDF). Furthermore, it’s now known not all NDF fiber is the same and degrades at different rates in a cow’s rumen.

Laboratory procedures are now available to determine those rates. Heat-damaged forage can also bind protein to fiber, making it less available in the rumen. Forage labs are able to determine how much protein is bound up in both the ADF and NDF, which provides additional information about the quality of the protein.

Forage laboratories have begun measuring the various pools of digestibility of the NDF fractions and separating them into 30-, 120- and 240-hour increments. The NDF digestibility (NDFd) varies considerably both between different species of forage (i.e., grasses versus legumes) and within species based upon growing conditions and maturity of forages from month to month and year to year.

All of this new knowledge has allowed dairy scientists to gain a better understanding of what they might expect rumen microbes to do with a given forage, enabling us to determine how much metabolizable energy to expect from a feedstuff’s fermentation. No longer does a TDN calculation for a forage provide the information needed to fine-tune a ruminant diet. Knowledge of the different nutrient fractions in forages enables us to predict what the dynamics of the rumen will be and how much milk a cow will produce or what the daily gain of a beef cow will be.

Today, a standard lab analysis includes moisture levels, CP, soluble protein, ADF, NDF, 30-, 120- and 240-hour NDFd, acid detergent insoluble protein (ADIP), neutral detergent insoluble protein (NDIP), fermentation acids, lignin, starch, sugar and fat, along with energy calculations and minerals. All of these data can be incorporated into computer models to evaluate rations and predict milk production or growth rates.

The digestibility of starch is also now being analyzed to determine the energy available, particularly from corn silages. The maturity of the corn grain and how quickly it is fermented in the rumen can have an effect on rumen health.

Many of the current assays being run in forage labs, such as fiber digestibility, starch and sugars, are the result of in vivo and in situ research being conducted on cows at research facilities. The complexities of the rumen fermentation continue to be unraveled as we learn more about how the different fractions of feedstuffs interact with rumen microbes.

Near-infrared reflectance spectroscopy (NIRS) allows laboratories to rapidly analyze samples for multiple nutrients. Since its humble beginnings, this computer-driven technology has evolved into an extremely powerful and accurate means of quickly testing forages and getting results back to farmers and nutritionists.

Forages must be analyzed by a competent forage-testing lab on a routine basis to monitor forage quality and ensure consistent diets are fed to our animals. The forage analysis industry works very hard to standardize procedures but, even so, there can be minor differences between labs. Farmers and nutritionists are advised to limit their business to one lab to maintain continuity of results.

Forage testing has come a long way in just a short period of time and has proven itself to be a useful tool for both growers and farmers, enabling them to establish the market value of their forages, and in determining the best way to utilize forages and balance a cost-effective diet in a feeding program.

As profit margins remain tight or nonexistent for the foreseeable future in much of animal agriculture, the economic value of forage has re-emerged as a key component in helping maintain profitability in a business. Testing forages for their nutritional value enables us to use those forages to their maximum potential in ruminant feed rations.  end mark

PHOTO: The economic value of forage has re-emerged as a key component in helping maintain profitability in the livestock business. Photo courtesy of Rock River Labs.

John Hibma
  • John Hibma

  • Consulting Ruminant Nutritionist
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