Neutral Detergent Fiber determinations in dairy cattle. Why are they important?

Neutral detergent fiber (NDF) is a measure of the proportion of cell wall in plant tissue, expressed as a proportion of total dry matter. Adequate NDF in dairy cow diets enables proper rumen function, but the challenge of feeding increasing neutral detergent fiber concentrations to high-producing dairy cows is that it may lead to excessive gut fill and limit feed intake.

The level of neutral detergent fibre in the animal ration influences the animal’s intake of dry matter and the time of rumination. NDF is the most common measure of fibre used for animal feed analysis. It measures most of the structural components in plant cells (i.e. lignin, hemicellulose, cellulose).

“When a forage has a very high NDF, it is negatively correlated with lower consumption. That is, the animal fills up faster. Forage with low Neutral Detergent Fiber means the cow has more food in the rumen and can produce more milk,” asserts Jorge Mario Noreña, agronomist and professor at the National University of Colombia in Medellín.”

Feed analysis laboratories offer these NDF digestibility assays, but they are time-consuming for the lab and therefore costly. To reduce the cost of acquiring these estimates, many laboratories offer near infrared reflectance spectroscopy (NIRS) predictions of ivNDFD as an alternative to “wet chemistry.”

Near infrared assessment of NDFD

NIRS instruments bounce specific wavelengths of light off feed samples and measure the light absorbed or reflected back. The patterns of absorption and reflectance are indicative of the chemical composition of the feed material tested. To make use of these patterns, reference feeds are analyzed both with wet chemistry methods and by NIRS, and prediction equations are built from those relationships. It is important to note that NIRS analysis cannot be more accurate than wet chemistry analysis from that particular lab.

Best practices for NDFD analysis

To get the most value from investments in NDFD analysis, it is important to consider the following:

• Use a forage testing laboratory that is certified. For example, in case of the USA, the certifying body is the National Forage Testing Association (NFTA).
• Use the same laboratory for all the analyses.
• Only compare ivNDFD within feed type.
• Compare feeds based on the same time point.
• Avoid using NIRS analysis for unusual samples.

NDF digestibility is mainly influenced by maturity:

• Legumes have less total NDF and lower NDF digestibility compared to grasses.

Conclusions

• Enhanced NDF digestibility of forage improves DMI and milk yield of dairy cows.
• Digestibility of NDF should be measured more routinely to assess forage quality.
• This information is particularly important to rank accurately forages that might vary in
  yield and different quality traits.

Source:Abstract taken and modified from“Making use of NDF digestibility analyses for dairy cattle diets.”