High uNDF Forages on the Way?

Rick Grant, President William. H. Miner Agricultural Research Institute

W H Miner Institute Dairy Barn

Dr Rick Grant Miner Institute
Dr. Rick Grant, Miner Institute

This article is presented with permission from the August issue of the Farm Report. To subscribe to the Farm Report, contact Rachel Dutil at [email protected] or 518-846-7121, ext. 115.

All summer long the rain hasn’t stopped, and now it is getting warmer too. A perfect combination to boost lignification and undigested NDF (uNDF).  It is increasingly likely that we will be feeding some significant amount of poorly digestible forage fiber this winter, and we need to start thinking about how to best do it. Although a relatively new tool, we need to make best use of the uNDF values that are now a fairly standard part of many farms’ forage analysis.

Indigestible NDF is highly lignified and the ratio of iNDF (measured as uNDF240om) to lignin is highly variable. The uNDF240om measure is more sensitive to growing environment, plant genetics, and maturity at harvest than simply lignin/NDF or (lignin x 2.4)/NDF. Indigestible NDF is sensitive to these three factors due to variable lignification and crosslinking of lignin and phenolic acids to hemicellulose. Recent work at Miner Institute and Cornell University shows that ester-linked paracoumaric acid and ether-linked ferulic acid reduce NDF digestion and are found in lower concentrations with bmr corn hybrids and lower quality grasses. In fact, the negative relationship between ether-linked ferulic acid content of fiber residues and in vivo dry matter digestibility reflects the existence of cross-linking from lignin to hemicellulose that inhibits NDF digestion. The nature and extent of these cross-links are associated with a specific hybrid, its maturity at harvest, and its interaction with the growing environment.

This makes uNDF240om highly useful for forage quality assessment and benchmarking. To-date, feedback from the field on the utility of uNDF240om as an accurate and sensitive indicator of expected dry matter intake has been positive. Feed companies have begun to report the forage uNDFom at 30, 120, and 240 h along with the mean and range so that a farmer or nutritionist may easily benchmark their forage against a larger population and anticipate whether dry matter intake will move up or down as cows are fed various inventories of forage.

Measured ranges in uNDF240om content for the major forage categories are continuously summarized and reported by forage testing laboratories. Here are the ranges that were reported by Dairy One Lab in their May 2015 newsletter:

  • Corn silage uNDF240om:

8.7% of DM; Range: 2.0 to 25.5% of DM

  • Legume silage uNDF240om:

17.6% of DM; Range: 5.5 to 31.7% of DM

  • Grass silage uNDF240om:

15.5% of DM; Range: 2.3 to 44.8% of DM

There is tremendous variation in uNDF240om that we need to capture when formulating diets and predicting cow response. Clearly, the static relationship of ADL x 2.4 is not accurate given the range in that relationship observed in forage testing lab data. For example, even though the mean relationship between iNDF and NDF is 2.45 for legumes, the observed range is 1.3 to 4.5. For grasses it is 1 to 7.2% - using a standard relationship would lead to erroneous estimates of forage energy value and potential dry matter intake. Clearly, assuming that a constant fraction of NDF (i.e, 2.4 x lignin) is protected by lignification is untrue for legumes, grasses, and corn silages based on accumulated laboratory data.

Understanding and using these basic relationships will be especially important this year, given the terrible cropping weather we’ve experienced so far in 2017.