Is crude protein in corn silage decreasing?

Posted on July 30, 2015 in Forage Foundations
By Pat Hoffman, Vita Plus dairy technical specialist
It is not uncommon to receive a forage analysis for corn silage that reports a crude protein content less than 6.5 percent.  In fact, we sometimes see crude protein content of corn silage dip below 6.0 percent.

In contrast, when we examine crude protein book values for corn silage, the value is supposed to be closer to 8.5 percent.

The economic implication of low crude protein in corn silage is relatively easy to calculate. When crude protein content in corn silage is 2 percentage units lower than expected (6.5 versus 8.5), a wet ton of corn silage is missing 14 pounds of crude protein.  With plant protein prices near $0.20 per pound, feeding corn silage with lower crude protein would increase supplemental feed costs by approximately $6 for each wet ton of corn silage fed.

So what is the story?  Are crude protein contents of our corn silages really getting lower?

This question is being asked by Vita Plus consultants and dairy producers alike.  We did a small, informal evaluation of laboratory records, corn hybrid evaluations and peer-reviewed research to see if we could find some answers.

First, we examined the average crude protein content of the 2014 corn silage crop across three laboratories.  The average crude protein content recorded at two Midwestern laboratories was 7.3 and 7.4 percent.  In contrast, the average crude protein content of corn silage recorded at an eastern laboratory was 8.2 percent.

We also examined online historical records of corn silage crude protein content at two of the laboratories and could not find a clear indication that corn silage crude protein was decreasing to any great extent.  Likewise, we examined the historical records of the University of Wisconsin’s corn hybrid evaluation and could find no clear indication of decreasing protein in corn silage.  While we did not go into great analytical detail, the empirical exercise demonstrated no large or obvious industry trend.

However, our project did find two very clear reasons as to why crude protein in corn silage can be low.

It seems that both plant population and nitrogen fertility can have a significant influence on corn silage protein content.

In a study at the University of Wisconsin, two hybrids selected for high- and low-quality characteristics were grown at five plant densities, ranging from 18,000 to 43,000 plants per acre. As plant density increased, dry matter yield increased, but crude protein decreased.  Crude protein contents of high-plant-density corn silages were 0.5 to 0.6 percentage units lower in crude protein.  In a similar study, Canadian researchers observed that corn crude protein contents were reduced greater than 1 percentage unit when corn was grown under high plant populations.

Two mechanisms reduce corn silage crude protein when corn is grown under high plant populations.

  • Crowded corn plants grow taller, which changes the leaf-to-stem ratio, favoring more stem and less leaf mass.
  • When corn is grown in high populations, it challenges the nitrogen fertility program to supply adequate nitrogen, which can directly affect corn silage crude protein content. Numerous research trials have shown that nitrogen fertility status of corn, especially at pollination, can have a dramatic effect on corn silage crude protein content.  This research has demonstrated that corn silage crude protein content can range by as much as 3 percentage units (i.e. 9.0 versus 6.0) depending on nitrogen fertility status.

With this information we can, at minimum, use some logic to understand why the crude protein of a particular corn silage maybe low.  It could be corn silage from a field planted at very high populations.  Perhaps the corn silage was planted in double rows or in narrow rows at extreme plant populations.  Maybe the field had excessive rainfall, which depleted the nitrogen and turned the corn yellow (the tell-tale sign of nitrogen deficiency).  Maybe the growing conditions were perfect, but the field just ran out of available nitrogen supply due to dry weather during pollination.

All combined, we could find no clear indication of an industry trend for lower crude protein in corn silage, but very solid research suggests growing corn under modern high plant populations and or conditions which negatively affect nitrogen fertility can affect corn silage crude protein content.

Category: Crop varieties
Feed quality and nutrition
Forage Foundations