Author
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Mertens, David |
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BERZAGHI, PAOLO - Universita Di Padova |
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Submitted to: International Silage Conference
Publication Type: Proceedings Publication Acceptance Date: 7/1/2009 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: High quality silages are often the keystone of rations for dairy cows. Rations for dairy animals may contain 10 to 90%; therefore silage quality, which encompasses all silage characteristics that impact animal performance, is often crucial in meeting the nutrient requirements for dairy production. Nutritive value, fermentation characteristics, pH, ammonia, and moisture all affect silage quality and many of these factors have been extensively discussed because they are modified by the ensiling process. Nutritive value, defined as the concentrations of nutritional relevant constituents, is primary determination of silage quality and is initially established at the time of harvest. Fiber content and digestibility, particle size, and variability have tremendous impacts on silage quality for dairy cows. Fiber is a nutritional term that is defined as the indigestible and slowly digesting fraction of feeds that occupies space in the alimentary tract. The detergent system of analysis was developed to measure fiber and the main advantage of neutral detergent fiber is that it separates feeds into almost completely digestible neutral detergent solubles and neutral detergent fiber that varies in digestibility. A simple summative equation demonstrates that fiber content and its digestibility are the major factors that affect the total dry matter digestibility of feeds. Legume forages are high in digestibility and intake because their fiber content is low, but the digestibility of legume fiber is also low. Grasses have higher fiber contents, but their fiber is higher in digestibility than that of legumes. Our ability to improve fiber or overcome its limitation will occur when we can effectively partition it into digestible and indigestible fractions and use the digestion kinetics to understand fiber digestion in the dynamic ruminal environment. Intake is often the limiting factor in dairy cow productivity and fiber can often limit the intake of forages. The NDF-Net Energy intake system was designed to estimate the maximum proportion of forage that can be included in a ration for al target level of milk production. The system works well to define the ration that maximizes the utilization of silage quality. Just as cows have a maximum capacity to utilize fiber in silages, they also have a minimum requirement for fiber, which is based on its ability to stimulate chewing and promote optimal rumen fermentation. Because silages are chopped, the particle size of silages is important in determining the effectiveness of fiber in promoting chewing activity. The physically effective neutral detergent fiber of silages is a valuable measurement in determining silage quality for dairy cows. Because silages are harvested with moistures that range from 40 to 75% and forages from multiple locations and maturities are often stored in a single storage unit, silage quality is often more variable than hays. The daily variation in silage dry matter and nutrient concentration is substantial, and can be a significant impediment to utilizing silage to maximize its quality. |
