Feeding Dairy Cows: In Vitro NDF Digestibility


This fact sheet has been developed to support the implementation of the Natural Resources Conservation Service Feed Management 592 Practice Standard. The Feed Management 592 Practice Standard was adopted by NRCS in 2003 as another tool to assist with addressing resource concerns on livestock and poultry operations. Feed management can assist with reducing the import of nutrients to the farm and reduce the excretion of nutrients in manure.

The Natural Resources Conservation Service has adopted a practice standard called Feed Management (592) and is defined as “managing the quantity of available nutrients fed to livestock and poultry for their intended purpose”. The national version of the practice standard can be found in a companion fact sheet entitled “An Introduction to Natural Resources Feed Management Practice Standard 592”. Please check in your own state for a state-specific version of the standard.

Conclusions reached regarding in vitro neutral fiber digestibility (IVNDFD) and its impact on lactation performance in a literature review for a symposium presentation at the 2006 ADSA/ASAS Annual Meeting (Shaver, 2006) were as follows:

  • IVNDFD has been related to > milk production across an array of different forages.
  • Milk production response to IVNDFD is thru DMI, and not energy density.
  • DMI and milk production responses to IVNDFD > in higher producing cows.
  • Benefits of brown midrib corn & sorghum silages for IVNDFD, DMI, and milk production have been observed consistently.
  • More IVNDFD/in vivo research is needed with legumes & other grasses.
  • Increased IVNDFD has not been fully exploited by researchers in trials attempting to maximize dietary forage or optimize forage mixtures, or by field nutritionists feeding higher forage diets with the aim of improving cow health.

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IVNDFD Analysis

Several commercial testing laboratories offer wet chemistry IVNDFD measurements. Ranges for IVNDFD of forages are presented in Table 1. The IVNDFD values are highly variable among and within forage types. Introduction of low-lignin, brown midrib hybrids for production of corn and sorghum silages has widened the variation in IVNDFD for these forage types (Oba and Allen, 1999b). NIRS calibrations for predicting IVNDFD on hay-crop forage and corn silage samples are available at some commercial forage testing laboratories. However, Lundberg et al. (2004) found poor prediction by NIRS of legume-grass silage and corn silage IVNDFD. It is hoped that NIRS calibration equations can be improved upon in the future.

The NRC (2001) recommended a 48-h IVNDFD for use in the NRC (2001) model, and for that reason we used 48-h IVNDFD measurements in MILK2000 (Schwab et al., 2003). However, debate continues within the industry about the appropriateness of 48-h vs. 30-h IVNDFD measurements. Some argue that the 30-h incubation better reflects ruminal retention time in dairy cows (Oba and Allen, 1999a) and that most of the in vivo trials that have evaluated effects of varying IVNDFD on animal performance also performed 30-h IVNDFD measurements (Oba and Allen, 2005). Labs and their customers also like the faster sample turn around that is afforded by the 30-h incubation time point. For that reason, and also for improved lab operation efficiency, a 24-h incubation time point is being employed by some labs. However, some argue that the 48-h incubation time-point is less influenced by lag time and rate of digestion, and thus is more repeatable in the laboratory (Hoffman et al., 2003). Hoffman et al. (2003) provided data on the relationship between 30- and 48-h IVNDFD measurements that showed a strong positive relationship (r-square = 0.84). But, the lab average at a specific incubation time point and the relationship between incubation time points within a lab can be highly variable among labs making the development of a universal incubation time point adjustment equation difficult. The average lignin-calculated corn silage NDF digestibility in the NRC (2001) is 59%. This reference point is important for adjustment of IVNDFD values from different labs and varying incubation time points so that the resultant TDN and NEL values are comparable to NRC (2001) values.

Average IVNDFD values for selected high-fiber by-product feeds (Peter Robinson, CA-Davis, personal communication) are presented in Table 2. The IVNDFD values are highly variable among these high-fiber by-product feeds. The IVNDFD values for these high-fiber by-product feeds were poorly related to lignin-calculated (NRC, 2001) NDF digestibility. High digestible NDF (dNDF; % of DM) for soy hulls and beet pulp relative to other high-fiber by-products suggest a high potential for using these ingredients at reasonable inclusion rates to partially replace forage with low fiber digestibility to increase diet dNDF. Monitoring and maintaining effective NDF in the diet is critical when employing this feeding strategy.

The distribution of 48-h IVNDFD for high-group TMR samples from commercial dairies analyzed at the University of Wisconsin Forage Testing Laboratory (Marshfield, WI; Hoffman, 2003) is presented in Figure 1 with an average IVNDFD of 57.2% of NDF. The IVNDFD range for these high-group TMR samples is wide and raises concern over intake limitations on the low end and lack of effective fiber on the high end. Analyzing for IVNDFD offers another tool for troubleshooting fiber status of dairy cattle diets.

Table 1. Variation within forages for neutral detergent fiber digestibility measured in situ or in vitro.
Forage IVNDFD (% of NDF)
Nocek and Russell, 1998 Legumes 31-63
Grasses 41-77
Corn Silage 32-68
Allan and Oba, 1996 Alfalfa 25-60
Whole-Plant Corn 30-60
Hoffman, 2003 (UWFTL) Legumes 35-65
Grasses 25-75
Corn Silage 40-75
Chase, 2003 (Dairy One) Legumes 34-57
Grasses 25-75
Corn Silage 45-64


Table 2. Content and digestibility of NDF for selected high-fiber by-product feeds.
Ingredient NDF, % DM1 IVNDFD, % NDF2 dNDF, % DM
Forages 40-60 30-60 10-35
Corn gluten feed 36 80(1)3 29
Distillers grains 39 75 (14) 29
Brewers grains 47 50(2) 24
Wheat midds 37 50(3) 19
Beet pulp 46 85(10) 39
Citrus pulp 24 85(2) 20
Soy hulls 60 90(2) 54
Whole cottonseed 50 50(36) 25
Cottonseed hulls 85 20(4) 17
Almond hulls 37 40(5) 15
1NRC, 2001.
230-h IVNDFD (% NDF) adapted from Dr. Peter Robinson, CA-Davis.


Figure 1. Distribution of 48-h IVNDFD (% of NDF) in data set of 377 high-group TMR samples from commercial dairies analyzed at UW Soil & Forage Analysis Lab, Marshfield, WI (Hoffman, 2003).



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  • Arieli, A., and G. Adin. 1994. Effect of wheat silage maturity on digestion and milk yield in dairy cows. J. Dairy Sci. 77: 237-243.
  • Aydin, G., R. J. Grant, and J. O’Rear. 1999. Brown midrib sorghum in diets for lactating dairy cows. J. Dairy Sci. 82: 2127-2135.
  • Bal, M. A., R. D. Shaver, H. Al-Jobeile, J. G. Coors, and J. G. Lauer. 2000. Corn silage hybrid effects on intake, digestion, and milk production by dairy cows. J. Dairy Sci. 83: 2849-2858.
  • Chase, L. E. 2003. Update on forage digestibility. Page 25 in Proc. 2003 Dealer Seminars. Cornell Univ. Coop. Ext. Anim. Sci. Mimeo Series. No. 223.
  • Chow, L., M. Oba, V. Baron, and R. Corbett. 2006. Effects of advanced in vitro fiber digestibility of barley silage on dry matter intake and milk yield of dairy cows. J. Dairy Sci. 89(Suppl.1):263(Abstr.).
  • Dado, R. G., and M. S. Allen. 1996. Enhanced intake and production of cows offered ensiled alfalfa with higher neutral detergent fiber digestibility. J. Dairy Sci. 79: 418-428.
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  • Shaver, R. D. 2006. Forage intake, digestion and milk production by dairy cows. J. Dairy Sci. 89(Suppl.1):298(Abstr.).
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  • Tine, M. A., K. R. Mcleod, R. A. Erdman, and R. L. Baldwin, VI. 2001. Effects of brown midrib corn silage on the energy balance of dairy cattle. J. Dairy Sci. 84: 885-895.

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This fact sheet reflects the best available information on the topic as of the publication date. Date 5-25-2007

This Feed Management Education Project was funded by the USDA NRCS CIG program. Additional information can be found at Feed Management Publications.

Image:Feed mgt logo4.JPG This project is affiliated with the Livestock and Poultry Environmental Learning Center.


Project Information

Detailed information about training and certification in Feed Management can be obtained from Joe Harrison, Project Leader, jhharrison@wsu.edu, or Becca White, Project Manager, rawhite@wsu.edu.

Author Information

Randy Shaver
Professor and Extension Dairy Nutritionist
Department of Dairy Science
College of Agricultural and Life Sciences
University of Wisconsin – Madison
University of Wisconsin – Extension

Reviewer Information

Jim Barmore – Nutrition Consultant
Pat Hoffman – University of Wisconsin