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The language of nutrition: NDFd (Neutral detergent fiber digestibility)

Philip Krueger Published on 06 May 2015

In layman’s terms,what does NDFd mean?

NDFd stands for neutral detergent fiber digestibility. NDFd is a tool to help benchmark fiber digestibility and compare the feeding value of forages. In the past, it has been referred to as digestible neutral detergent fiber (dNDF) or cell wall digestibility (CWD).

How is NDFd measured?

In vitro analysis, or wet chemistry, is the preferred method for measuring NDFd. This method mimics rumen digestion. The forage sample is dried, ground and incubated in rumen fluid for 12, 24, 30 or 48 hours.

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Thirty hours is the most common measurement for forages fed to dairy cattle because that is the average time forage remains in a high-producing cow’s rumen. The digested fraction of the forage is the difference between the initial and final amount of neutral detergent fiber (NDF) left in the sample.

Wet chemistry analysis is very accurate, but it is expensive and time-consuming. Most labs offer a faster, less expensive NDFd test via near-infrared (NIR) spectroscopy. NIR estimates NDFd by bouncing infrared light off of a forage sample.

Results are based on calibration equations developed by using in vitro analysis. Accuracy depends on a robust NIR calibration database and an accurate definition of the sample. NIR NDFd analysis usually reduces the range of results and is often less accurate.

Each lab has different procedures to determine NDFd. There is usually variation between labs, so avoid comparing results from different labs.

How does NDFd impact the ration?

NDFd becomes more critical as more forage is fed. Early lactation cows cannot meet their daily energy requirements, so feeding forages with high NDFd encourages higher dry matter intake (DMI), minimizing bodyweight loss and the excessive need for supplemental grains and fats. High-NDFd forages provide more calories and allow cows to consume more NDF from forage. High-forage diets that are high in NDFd are typically more economical than other options.

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Explain what this does in the ration.

NDFd is key to DMI and milk yield. Michigan State University research has demonstrated that for every percentage point improvement in total diet NDFd, we can expect DMI to increase by 0.26 pounds per cow per day and milk production to increase by 0.47 pounds per cow per day.

Corn silage is the primary forage in U.S. dairy rations, usually ranging from 50 percent to 90 percent of the forage in diets. NDFd variations in corn silage are primarily due to hybrid genetics. BMR hybrids, for example, are bred specifically for high digestibility. Environmental growing conditions also affect digestibility.

This simple example (Table 1) uses two corn hybrids as the only variable to demonstrate how a hybrid with higher digestibility can enhance DMI and milk yield.

corn silage hybrids

Assumptions: Corn silage accounts for 80 percent of the forage in the diet on a dry matter basis, with good-quality haylage making up 20 percent. The base diet, containing Corn Hybrid A, has 60 percent total forage.

Multiplying 13 percent higher NDFd of Hybrid B x 80 percent of the forage being corn silage x 60 percent of the diet being forage = 6.2 points increased NDFd of the entire diet x 0.26 pounds DMI per point improvement = 1.6 pounds increased DMI per day. Increased NDFd of 6.2 points x 0.47 pounds of milk per point = 2.9 pounds more 4 percent fat-corrected milk (FCM).

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Assuming feed costs of $0.09 per pound of DMI and a milk price of $0.18 per pound, Hybrid B costs $0.14 per cow per day more for feed, but it will increase milk income by $0.54 per cow per day. That translates to a margin increase of $0.40 per cow per day.

What else should dairy producers know about NDFd?

Although most nutritionists and many dairymen have a good understanding of the NDFd concept, it can be challenging to measure NDFd and formulate diets. Starch, NDF and DM content vary from field to field, hybrid to hybrid and over time in storage.

Producers should monitor NDFd regularly in all forages as they are fed and adjust diets accordingly. PD

phil krueger

Philip Krueger
Dairy Nutritionist
Mycogen Seeds

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