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Forages: Harvest & Storage -
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| Author: | OMAFRA Staff |
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| Creation Date: | 01 March 2002 |
| Last Reviewed: | 01 March 2002 |
| Agronomy Guide > Pub 811: Forages > Harvest & Storage - Forage Quality & Harvest Timing |
The type of livestock being fed determines the appropriate quality of forage. Match forage quality to the nutritional requirements of the animal. For a high-producing dairy herd, quality feed, which is high in digestible energy and protein must be produced. The benchmark analysis for alfalfa for high-producing dairy cows is considered to be 20% crude protein (CP), 30% acid detergent fibre (ADF), and 40% neutral detergent fibre (NDF). For a beef cow, the most appropriate hay is more mature and higher yielding, and is therefore lower in protein and digestibility. Many recreational horse owners prefer hay that is more mature and contains more grass than is common in dairy hay, but it is very important that it be entirely free of mould and dust. Some markets also require the hay to be green in appearance and entirely free of weeds. The remainder of this section will use the term "high quality" to mean high in protein and digestible energy.
Laboratory analyses of forages is essential for accurate ration formulation. The nutrient content of forages varies greatly depending on the type, stage of maturity at cutting and how well it is preserved.
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An expression of feed nutrient content with the moisture included. Nutrient content on an "as-fed" basis is always lower than on a "dry-matter" basis.
An expression of feed nutrient content after the moisture has been removed by drying. Used to compare nutrient composition or animal intake of feeds differing in moisture content.
An estimate of the total protein content of a feed. Determined by analyzing the nitrogen content of the feed and multiplying the result by 6.25. Crude protein includes true protein and other nitrogen-containing substances such as ammonia, amino acids and nitrates.|
The amount of residue (primarily cellulose and lignin) left after boiling a feed sample in an acid detergent solution. The ADF value is used to predict the energy content (TDN, NE) of forages.
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The insoluble fraction containing all plant cell wall components left after boiling a feed sample in a neutral detergent solution (primarily hemicellulose, cellulose and lignin). NDF is used to predict ruminant feed intake.
RFV is calculated using ADF and NDF. The relative feed value for grasses is usually lower than for legume forages, due to the higher fibre values. For this reason, it is questionable to compare the relative feed value of different species.
The amount of feed energy actually available for animal maintenance and production. It represents the energy fraction in a feed left after fecal, urinary, gas and heat losses are deducted from the gross energy value of a feed.
A term describing the energy value of feedstuffs using regression equations.
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A laboratory test used to measure the amount of heat-damaged protein in hay and haylage.
A measure where a forage sample is incubated in rumen fluid for a given period of time to simulate digestibility in rumen conditions.
The digestibility of the fibre is determined by in vitro NDF digestibility. This impacts both digestible energy of the forage and animal intake.
Fermentation profile analysis is available for silage to determine relative amounts of lactic, acetic, butyric, propionic acids and pH.
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Corn silage is unique in that it consists of a mixture of two very different components - high moisture grain corn and stover. High digestible energy is important to reduce the need for supplemental grain. Lower NDF and increased dNDF are important for increased intake, as well as energy.
Digestible energy of corn silage is primarily determined by the relative amounts of starch and fibre (NDF) and their digestibilities. ADF is sometimes used to estimate energy, and NDF is used to estimate intake, but these measures alone do not consider digestibility. Newer methods more accurately estimate corn silage digestible energy using CP, fat, non-structural carbohydrates (NSC), NDF and lignin. Other methods are used that also use starch and in vitro NDF digestibility (dNDF). Kernel texture, moisture and processing influence starch digestibility.
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The timing of the harvest is the most important consideration when trying to produce quality forage. Forage crops decline in feeding value as they mature. For instance, once alfalfa buds appear, feeding value will decline about 0.2% per day in protein and about 0.4% per day in digestibility (see Table 5-11. Digestibility and Protein of Alfalfa and Bromegrass at Various Stages of Maturity). Short delays in cutting result in significantly lower forage quality. Of course, finding a window of dry weather can complicate things even further.
As a general rule of thumb, high-quality, first-cut forage should be cut at mid-bud to full-bud stage.
The timing of cutting is determined by the nutritional requirements of the livestock being fed.
Cutting at the pre-bud or early-bud stage will result in reduced yields and may increase the risk of losing the stand. Extremely low fibre levels may result in nutritional problems. With grasses, a compromise between yield and quality occurs at "early head emergence from the boot." Orchardgrass will mature much earlier than timothy and bromegrass. Delayed harvesting of forage will give higher yields and greater plant persistence, but lower feed quality. With a large acreage of forage, it is advisable to start cutting earlier to ensure the later cut material will still have adequate quality.
Subsequent second and third cuttings of alfalfa may be in intervals of approximately 30 days (mid-bud) to 40 days (early flower) or more, depending on whether the goal is high quality or maximum persistence and yield. (See the section Forage Winterkill)
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Methods used to determine when to begin cutting first-cut alfalfa include the calendar date, stage of development (mid-bud, full-bud), growing degree days (GDDs) (see the section Growing Degree Days), scissors cut, and the Predictive Equations for Alfalfa Quality (PEAQ). The PEAQ method uses the longest stem and the most mature stem to estimate the NDF of the alfalfa in a standing crop.
Many base cutting decisions using NDF as the primary quality variable. For high-producing dairy cows, optimum alfalfa NDF for intake and dietary fibre is approximately 40%. With warm weather, NDF can increase about 0.7 units per day, and therefore quality can drop rapidly. NDF can vary from 1 year to the next by up to10% when cutting is on the same date. The relationship between morphological stage, such as early or late bud stage, and NDF is not always high.
A PEAQ stick has been developed, that incorporates the NDF estimates onto an easy-to-read measuring stick, which can be used in the field. PEAQ is intended for use as a tool in making cutting decisions and is not meant to replace forage analysis and ration balancing. For details on how to use the PEAQ system, refer to Predicting Alfalfa Quality Using PEAQ on the OMAFRA Web site at www.omafra.gov.on.ca/english/crops/field/forages.html.
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