Fibre Digestibility - Moving Forward!

The methods used to evaluate the digestible energy of forages are evolving. For many years we have used ADF and NDF to predict digestible energy. These are measured by wet chemistry techniques, as well as the cheaper and faster Near Infrared Reflectance Sprectroscopy (NIRS) method. While ADF and NDF are good measures of the amount of fibre in a forage, they do not measure how digestible that fibre is. Fibre digestibility is determined by measuring the NDF digestibility (dNDF) during an in vitro fermentation in rumen fluid. Researchers have also developed techniques for measuring dNDF using NIRS. In vitro NDF digestibility analysis is currently available from commercial feed testing labs.

NDF digestibility gives us more accurate estimates of TDN, NE and intake potential. Increased NDF digestibility will result in higher digestible energy and increased forage intakes. Ration balancing is more precise, with more predictable animal performance. It also gives us the tools to better compare different forages. If you have two haylage samples that both analyze 19% CP, 31% ADF and 42% NDF, would they be considered equal? If NDF digestibility analysis results are available, and Forage #1 has dNDF of 40%, and Forage #2 has dNDF of 60%, we know there is a lot more milk or gain in Forage #2.

Like the % NDF, maturity and harvest timing have the greatest influence on fibre digestibility. Early cut forage will have higher fibre digestibility than later cut forage. The NDF digestibility of alfalfa haylage can range from 35 to 70%. In general, grasses and corn silage will have higher NDF digestibility than legumes due to less lignification. Growing conditions, such as temperature and moisture will also affect lignification and NDF digestibility. First cuts tend to have higher fibre digestibility than later cuts.

Consider requesting NDF digestibility when sending your forage samples away for analysis. Talk to your commercial forage testing lab and your nutritionist to discuss using this technology to improve forage quality, ration balancing and livestock performance.

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