Harvesting Forage: Don’t “just do it”-Do it RIGHT!

Harvest and storage management have tremendous effects on silage quality. High forage quality drives intake in feedlot cattle and in turn, drives production. There are many factors in implementing a successful forage management system. In this article we will focus on two that have the biggest impact on an ideal fermentation.

Harvesting forages at optimum maturity and moisture is crucial in obtaining the best silage possible. Corn silage should be harvested when the whole plant is 65%-68% moisture and the kernels are at ½ milk line. However, milk line and whole plant moisture do not always match up. In all cases, whole plant moisture should always be the overriding factor for corn silage harvest. Depending on conditions, corn silage will dry down at a rate of about 0.5% per day.
How do we determine whole plant moisture? The most accurate way to determine whole plant moisture is to chop a sample and dry it down in a Koster tester or a microwave. Be sure your sample size is large enough to produce sufficiently small particle size when you run it through the chopper.

Why is moisture level so critical? Harvesting corn silage that is too wet (typically >70% moisture) results in excessive fermentations that produce high concentrations of acids and result in nutrient run off. Specifically, these wet corn silages are often characterized by high concentrations of acetic acid produced from “wild type” fermentations. These wet silages also typically have a high total acid content, which can lead to a reduction in dry matter intake. In contrast, extremely dry corn silage (<60% moisture) should be avoided because low moisture restricts fermentation and is more difficult to pack, which often leads to poor aerobic stability.
Moisture levels in alfalfa silage are even more critical. Wet alfalfa silage is highly prone to clostridial fermentation resulting in butyric acid production. NEVER harvest alfalfa haylage at moistures >70%.

Particle size is the second factor for discussion. From a fermentation standpoint, silage can’t be too fine. From an effective fiber to the cow standpoint, it can definitely be too fine. So what is ideal particle size? This answer may be different for every farm and every harvest season. The important thing is knowing when and how to adjust it while harvesting. Particle size adjustment is directly related to plant moisture content. As moisture content decreases, particle size should decrease as well. This will help increase density and displace oxygen, ultimately leading to a better environment for fermentation. There is no excuse for not adjusting particle size while harvesting if necessary. All modern forage harvesters make it very easy to change the length of cut. Harvesters should also be maintained to provide a consistent length of cut. Yes, knives do get dull and shear bars do wear out. Don’t try to stretch either. Keep your knives sharp and your shearbar tight. Recommendations for theoretical chop length at ideal moisture usually run between ½ and ¾ inch for corn silage and up to 1 inch for alfalfa haylage.

The keys to making high quality silage include: 1)rapidly excluding air from the forage mass, which will result in 2) a rapid production of lactic acid and reduction in silage pH, and 3) to prevent the penetration of oxygen into the silage mass during storage. Excessive oxygen due to overly dry forage or forage chopped too coarsely allows the plant to respire for extended periods of time. This results in utilization of sugars and excessive degradation of plant protein. Oxygen also encourages the growth of undesirable microbes such as yeasts and molds.

by Robert Davis, Agri-Basics, Inc., Nutritionist