Editor's note: The following information was provided by Dairyland Laboratories in Arcadia, Wis.

It's no secret that the starch degradability of ensiled grains changes over time. As grains mature, the starch molecules are encapsulated in a prolamin-protein matrix that limits the ability of rumen microbes to digest the starch. This reduces the amount of VFAs and microbial protein produced from each pound of grain. Fortunately, the lactic and acetic acids produced during the ensiling process will dissolve prolamin over time, leaving the starch in a more degradable form.

Intuitively, nutritionists have known for years that high-moisture corn and corn silage change over time, but until recently there has not been a reliable method for quantifying this change. Now, the development of a 7-hour in vitro starch degradability test has provided us with more information about when and how much starch degradability changes throughout the year.

The chart below shows the results of over 11,000 corn silage samples analyzed by Dairyland Laboratories Inc. from the 2010 harvest season. Clearly, starch degradability and protein solubility have increased over time. The implications of this change can be dramatic. Consider the increased amount of rumen degradable starch from the average corn silage sample since September. If these degradabilities were applied to all of the starch in a 28 percent starch ration at 50 pounds of dry matter intake, the amount of rumen degradable starch would have increased from 9.8 to 11 pounds.

Or, put another way, we could be feeding 1.7 pounds less corn in March and the rumen would be experiencing the same amount of available starch.

Seven-hour in vitro starch degradability (IVSD 7hr) is just one of the many tools that nutritionists have available to help maximize the efficiency of starch use in dairy rations. It is important to remember that this test only speaks to the chemical properties of starch and is best used in conjunction with particle size evaluation. To apply these results on a dairy farm, it is helpful to establish a baseline value at harvest to make adjustments as the values increase throughout the winter months.

Corn silage averages for the 2010 crop year (Dairyland Laboratories Inc.)

Monthly Average N

as % of CP

Starch IVSD as %
of starch
IVSD 7-hr.
Sept. 10 2390 25% 34% 78% Low
Oct. 10 2065 29% 32% 80% Medium
Nov. 10 1008 32% 34% 82% Medium
Dec. 10 1198 42% 32% 85% Medium
Jan. 11 1840 43% 33% 86% Medium
Feb. 11 1348 47% 34% 87% High
March 11 1598 48% 33% 88% High