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Two situations were reported this spring that may fit your farm or feeding program.    Both have a common thread of forage quality and ration balancing.

Situation 1.  Sam called about a client experiencing mid-lactation displaced abomasums (DA).   Production is excellent (over 24,000 pound rolling herd average) with a nutrient dense TMR containing brown mid-rib corn silage, western hay, hominy, soy hull pellets, wet brewers grain, and a protein-mineral-vitamin pack.  The Penn State top box (measures long forage particles over 0.75 inch) had 15 percent in this box (mainly processed corn silage).  Little western hay was on the top box.

Situation 2.  Joe was exciting about adding his “new ingredient” to his high group TMR, one pound of chopped wheat straw.   After adding straw, dry matter increased along with milk components (milk fat test increased from 3.3 to 3.6 and milk protein increased from 3.0 to 3.1) while milk production per cow exceeded 90 pounds.

The Role of Forage
Forages are included in dairy cow rations to provide a forage or “hay” raft in the rumen, maintain rumen health and fermentation, lower feed costs, provide nutrients for rumen microbial to produce protein and VFA (volatile fatty acid) for energy, and stimulate cud chewing (buffering the rumen with sodium bicarbonate).   Every year dairy managers can select new forage varieties that may increase yield and nutrients available to the cow.   At the World Dairy Expo, the winning alfalfa samples have been over 210 RVF (relative feed value), crude protein levels over 25 percent, and NDF (neutral detergent fiber) levels below 35 percent.   We refer to these as cotton candy or rabbit forage as it can be rapidly fermentable in the rumen and may not meet two critical forage roles, maintaining the rumen forage mat and stimulate cud chewing.

In an article written by Dr. Peter Van Soest (retired fiber researcher at Cornell University), he referred to high producing cows as having a “lignin” requirement.  Initially, this seemed wrong.   Lignin has a digestibility value of near zero, provides little nutrient value, and takes up space in the rumen.   But, lignin will remain in the rumen longer than “cotton candy forage” contributing to rumen health and cud chewing.  Could this be the common factor in Sam’s and Joe’s situation?

New Forage Tests
NDF (neutral detergent fiber) digestibility or NDFD is the percent of NDF that is digested in the rumen.   You may see this measurement on your forage test results.  Two different methods may be reported on your forage analysis.
 

a.       A 30-hour in vitro digestibility test measures the forage NDF digested or fermented in a glass container containing rumen fluid for 30 hours.   Thirty hours represent the normal digestion time for forages in the rumen.

b.      A 48-hour in vitro test represents the maximum amount of digestible NDF that may occur.   It will be 6 to 8 units higher than the 30-hour test.

Either test will estimate digestible NDF.  A new term representing this value is NDFD.  A higher NDFD value is desirable as it indicates high quality forage.  Table 1 lists forage values for 2002-2003 year from Dairyland Labs.

Table 1.  Average and range of NDFD values for forage crops
   Forage Type                              Average                             Range

Mixed hay	47	32-62
Legume hay	46	32-61
Grass hay	55	38-73
Corn silage	60	48-71

An example could be alfalfa haylage testing 60 percent NDFD.  This high quality forage would have less rumen bulk, less cud chewing, and a faster rate of passage.   These characteristics reflect high quality forage, but ration must be balanced to effectively utilize these “super” forages.  Do not confuse this value (60% NDFD) with the chemical NDF level (for example 40 percent NDF).

The amount of digestible NDF in a forage can be calculated by multiplying the amount of NDF in a forage (for example 40 percent NDF in alfalfa listed above) times the NDFD or NDF digestibility (for example 60% NDFD listed above).  This alfalfa haylage sample would contain 24 percent dNDF (60 percent NDFD times 40% chemical NDF) that represents the quantity of digested NDF in forage.  If a cow consumed 20 pounds of haylage dry matter, she receives 4.8 pounds of digestible fiber (dNDF) and 3.2 pounds of undigested NDF.  The total amount of NDF in the 20 pounds of alfalfa haylage is 8.0 pounds (20 pounds time 40 percent chemical NDF).

Now, put your thinking cap on! Does a dairy cow have a need for both types of NDF in her ration?