NDF Digestibility: adding to the knowledge base Mike
Rankin Although NDF digestibility has been around for a long time as forage qualitative trait, it’s really just been the last two years that producers, agronomists, and feed nutritionists have seen it on a routine analysis of forage quality. NDF digestibility has effectively replaced acid detergent fiber (ADF) as a measure of overall forage digestibility. Of course, we need to keep in mind that NDF digestibility, by itself, is rather meaningless and total NDF content of the forage is still the most important factor in determining overall forage quality. For example, a forage with 40 percent NDF is generally of higher quality than a forage with 60 percent NDF. However, knowing both the NDF and its related digestibility percentage is a great help in sorting-out forages the with same or similar total fiber values. What have we learned in two years? With a multitude of forage samples analyzed for NDF digestibility during the past two years, we’ve been able to start putting some of the pieces of the puzzle together in terms of what factors impact NDF digestibility and what are some reasonable benchmarks to strive for. First, let’s look at maturity. Pat Hoffman, UW Extension Dairy Scientist, reports that the rate of decline in NDF digestibility differs with species. For example, grasses and small grain forage have very high NDF digestibility while vegetative but decline rapidly with advancing maturity. This trend is shown for small grains in Fig. 1.
Figure 1. Effect of maturity stage on 48h NDF digestibility of small grain silage.
For legumes like alfalfa, NDF digestibility is less compared to grasses during early stages of growth but declines at a slower rate. These trends don’t really change our thinking on optimum harvest timing for forages, but they do reinforce the importance of harvesting at the proper maturity (boot for grasses and bud for legumes). As forages mature, plants accumulate more NDF that becomes less digestible and results in a significant drop in energy derived from the forage. What’s good and what’s not so good? As more samples get analyzed for NDF digestibility, it becomes possible to develop reference values. By doing so, producers can compare their values to those obtained from a larger database. Using values derived from samples analyzed at the Marshfield Soil and Forage Testing Lab, Pat Hoffman recently published the following average values and ranges for various forages and total mixed rations.
What about corn silage? Joe Lauer, UW Extension Corn Specialist, recently looked at several management factors to determine their impact on NDF digestibility. The management factors studied included hybrid selection, planting date, plant density, row spacing, and harvest date. Of these, planting date, row spacing, and plant density effectively had no impact on NDF digestibility. Like legumes and other grasses , harvest date had a significant effect on NDF digestibility, with the highest values occurring near flowering and then declining with advancing maturity. The one management factor that did show promise for improving NDF digestibility was hybrid selection. In fact, there was a wide variation among the silage hybrids tested in the UW performance trials in 2002. The range in NDF digestibility was about 56 to over 68 percent, with the highest falling into the brown mid rib category.
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
For
more information contact 
