Looking at corn silage through the lens of true forage

By Dr. Michelle Chang-Der Bedrosian, Vita Plus forage products and dairy technical services, and Pat Hoffman, Vita Plus dairy techncial services

Forage – the foundation of a dairy cow’s diet – is heavily impacted by variations during the growing season.  The emerging concept of “true forage” can be a highly effective tool for both the nutritionist and dairy producer.

What is true forage?    

Corn silage is a combination of forage (stalk, leaves, tassels and cob) and grain (corn kernels).  Traditionally, we analyze corn silage nutrients using a sample of the whole plant mixture.  The challenge is that nutrients in the mixture often are largely dependent on the starch content of the sample, making it difficult to figure out the real forage quality.  For example, is the corn silage actually low in uNDF240 (undigested neutral detergent fiber after 240 hours) or does it just have a lot of starch in it?

When evaluating the true forage portion of a corn silage sample, simple calculations are used to remove the non-forage portions of the plant to allow for a clearer evaluation of actual forage quality.

Looking at the economics

High-quality, homegrown forages are paramount to any discussion of optimizing the economics of a dairy cow diet.  From a nutritionist standpoint, it is much easier to manipulate total and digestible starch in the diet.  It is more difficult to manipulate digestible NDF and poor-quality NDF in forage is expensive to fix.  Thus, maximizing forage quality often reduces feed purchases.

On-farm hybrid evaluation

Many farms internally compare hybrids, fields, or corn silages from different growers by focusing on milk per ton or milk per acre.  These rankings are solid tools, but they’re based on “whole plant” analysis and are heavily influenced by the concentration of starch and fat in the sample.

Corn silage can also be ranked by milk per ton of true forage.  Because this process does not consider starch, it is much easier to see the differences in corn silage forage quality when looking at milk per ton of true forage only.  This is much more useful when focusing on the goal of optimizing true forage quality.  Starch and yield differences can be estimated using other metrics and approaches.

Improve forage quality

We need to better understand how environment and field-based corn silage practices influence forage quality.  Here are a couple examples:

1. Corn fields that are infested with northern corn leaf blight or tar spot typically have reductions in both yield and NDF digestibility.  Fungicides can improve plant health, but those applications obviously come at a price.  Evaluating the forage quality benefits of fungicide applications may be somewhat easier by looking at the nutrient composition of the true forage fraction of corn silage.
2. Reducing the plant population in corn silage may improve NDF digestibility because, by spreading out the plants, the corn grows shorter with smaller internode distance.  Thus, plants have more leaves and the stalk diameter is altered.  However, this may come at the cost of reduced yield and, as such, we need great tools to evaluate whether this management practice makes economic sense.

For dairies wishing to internally evaluate corn silage management practices, breaking the corn silage down and evaluating the true forage quality can lead to great discussion on how to improve forage quality.  The bottom line is that we know poor-quality corn silage is expensive to fix, so any metric to better evaluate corn silage and help dairy farms improve income over feed cost is worth consideration.

This article was originally written for the July 2021 issue of Hoard’s Dairyman.