What is NDFD?
NDFD is a measure of the digestibility of the NDF fraction of the diet. It can have significant effect on the amount of energy available from forages in the diet. It can have an effect on dry matter intake – especially if it is too low. This can lower rumen flow rates and lead to decreased milk production or body weight loss.

Why use NDFD?
NDFD is used to assess the energy level of the diet. This allows for more accurate ration balancing for desired production levels. It can be used as an evaluation tool for low production. It allows selection of forages appropriate to need – high NDFD for lactating cows and lower NDFD to dry cows and heifers.

What affects NDFD?

Plant maturity is the primary factor. More lignin means lower digestibility. Leaf to stem ratio is also important. Leaf NDF is more digestible than stem NDF. As forages mature, there is more stem than leaf in the plant. Select hybrids/varieties for digestibility. Be sure to harvest at optimum maturity. This means grasses in boot stage, alfalfa in late bud and corn silage at half milk line. However, do actual moisture checks on corn silage because milk line on newer hybrids is not that reliable.

How is NDFD measured?
It can be done in rumen fluid (in vitro) or with NIRS. Should one use 30 hour or 48 hour digestion? Both have strengths and weaknesses including turnaround time, variability and repeatability. There is a fairly high correlation between 30 and 48 hour. The key is to pick one method and be consistent. Also, there are differences between laboratory analyses so it is best to pick one laboratory and stick with it.