Interpreting Lab Results

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Source: Beef Cattle Research Council

Most labs provide basic information on moisture content, protein, energy, total digestible nutrients, fibre, and some vitamins and minerals. More specialized tests may include results for pH, ADIN, nitrates, toxins, relative feed value (RFV), and other parameters.

Dry Matter (DM, %) refers to the moisture-free content of the forage sample. The water content of forage will dilute nutrients, yet doesn’t usually have a great impact on animal intake, therefore it’s important to balance all rations on a dry matter basis. The daily intake of beef cattle will be ~2%-2.5% of body weight on a dry matter basis. Moisture contents outside of expected ranges can indicate potential spoilage issues. Wet grains (40% DM) silages may not ensile well leading to heating, clostridia or listeria contamination or excessive aerobic losses and spoilage.

Organic Matter/Ash (%) is derived by determined the DM component. Measuring the ash content allows the sample to be split into organic matter and inorganic (mineral) components. Excessive ash content (>6-8%) can indicate soil contamination in the sample.

Crude Protein (CP, %) is an estimate of protein based on multiplying nitrogen content of the sample by 6.25 (the nitrogen content of protein is ~16%, 100 ÷ 16 = 6.25). Protein digestibility can vary and proteins may be bound in indigestible forms (e.g. heat damaged proteins). Non-protein nitrogen (NPN) sources like ammonia or urea increase crude protein values but depend on microbial activity and dietary starch to have any nutritional value.

Neutral Detergent Fibre (NDF, %) indicates the amount of fibre content in the plant. High levels of NDF (above 70%) will restrict animal intake. More mature forages will have higher NDF levels.

Acid Detergent Fibre (ADF, %) measures the least digestible portions of the forage plants, such as cellulose and lignin. High ADF indicates poor digestibility of the feed. High quality legumes generally have ADF values between 20-35%, while grasses can range from 30-45%.

Acid Detergent Insoluble Nitrogen (ADIN, % of total protein) also referred to as acid detergent insoluble protein, acid detergent insoluble crude protein, acid detergent fibre protein, insoluble protein or bound protein) is a measure of heat damage that can bind protein and make it unavailable to the animal.

Total Digestible Nutrients (TDN, %) is defined as digestible carbohydrate + digestible protein + (digestible fat x 2.25), reflecting the greater caloric density of fat. A TDN value can be converted into estimates of digestible, metabolizable, or net energy. It’s most useful and accurate for rations comprised primarily of plant-based forages.

Relative Feed Value (RFV) is an index that estimates intake and digestibility and is useful for evaluating 100% alfalfa hay or silage only, with full bloom alfalfa hay used as the baseline with a RFV of 100. Values below 80 normally will not meet animal requirements for energy. It is not reliable for mixed hay, grass hay or cereal greenfeed. It is often used for price discovery but is not helpful when balancing rations.

Relative Forage Quality (RFQ) is an index that estimates intake and TDN. The estimate of intake is based on different equations for grasses versus legumes or legume-grass blends and includes additional factors to improve the accuracy of prediction, as well as in vitro measures of NDF digestibility. RFQ can be used for legume, grass, and legume/grass mixtures. The RFQ value for full bloom alfalfa hay will be similar to the RFV, but when samples differ in NDF digestibility, RFQ will differ from RFV.

Many feed analysis reports will include calculations of digestible energy, metabolizable energy, net energy for gain, net energy for lactation, and net energy for maintenance. Differences in the way these are calculated may exist between labs. You can input your forage results into the calculator at the top of the page to see if it is suitable to feed to cattle as is or if you will need to blend with other feed.

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