cattle, as can weather conditions like precipitation, temperature and wind speed, or environmental fac tors such as mud depth, bunk space, or other fac tors. An example of nutrient requirements for cows compared to bred heifers is in the following table. A common rule of thumb is 55-60-65 and 7-9-11 for the percentages of TDN and CP, respec tively, required by a beef cow in early-, mid-, and late gestation.
* Values are from w w w.BeefResearch.ca and were generated using Alber ta Agriculture’s CowBytes Program, with assumptions including breeding for June 1 calving, typical Canadian winters, access to shelter from wind and a daily gain of 1.25 pounds for bred heifers in addition to weight gain from pregnanc y. Interpreting Lab Results Laborator y results are often repor ted on both a “Dr y Matter ” and an “As-Fed” basis. Dr y Matter (DM) refers to the moisture -free nutritional content of the sample. Always formulate rations on a DM basis. 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. Dr y 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 impac t on animal intake, therefore it ’s impor tant to balance all rations on a dr y matter basis. The daily intake of beef cattle will be ~2%-2.5% of body weight on a dr y matter basis. Moisture contents outside of expec ted 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.
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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 var y 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 ac tivity and dietar y 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 restric t animal intake. More mature forages will have higher NDF levels. Acid Detergent Fibre (ADF, %) measures the least digestible por tions 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 2035%, 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), reflec ting the greater caloric density of fat. A TDN value can be conver ted into estimates of digestible, metabolizable, or net energy. I t ’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. I t is not reliable for mixed hay, grass hay or cereal greenfeed. I t is often used for price discover y 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 fac tors to improve the accurac y of predic tion, as well as in vitro measures of NDF digestibility. RFQ can be used
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