Dr. Bill Weiss, Dairy Nutrition Specialist, Ohio State University
Dairy producers that feed corn silage must make several important decisions regarding corn silage harvest in the upcoming weeks. These decisions must be made whether dairy farmers harvest the corn themselves, have it custom-harvested, or purchase the forage. Questions that must be answered include:
1. When should the corn be harvested?
2. How high should the plants be chopped?
3. What is the correct chop length (particle size)?
4. Should the material undergo kernel processing?
5. How long should the silage be left undisturbed after filling?
The use of inoculants also should be considered. See the Corn Silage Update article in the September, 2003 edition of Buckeye Dairy News for details.
When should the corn be harvested? Corn plants should be chopped when they reach the correct dry matter concentration. The ideal dry matter for corn silage is between about 30 (for bunkers) and 38% (uprights). See the Corn Silage Update article in the September, 2003 edition of Buckeye Dairy News for details.
How high should the plants be cut? The least digestible part of the corn plant is the stalk. It has high concentrations of neutral detergent fiber (NDF) and lignin. When cutting height is increased, more stalk is left in the field which reduces the proportion of corn silage that is stalk and increases the proportion that is leaves and ears. Typical stubble height for corn is 4 to 6 inches and most of the research on high cut corn had stubble heights of 15 to 18 inches. Based on research studies:
- High cut reduces dry matter yield 4 to 6% (this means production costs for the silage will increase 4 to 6% per ton of dry matter),
- High cut will increase dry matter concentration by 2 to 4 percentage units,
- High cut will decrease NDF concentration by 2 to 4 percentage units and increase starch by about 2 percentage units, and
- High cut will decrease lignin concentration slightly and usually increases in vitro NDF digestibility.
When high cut and low cut were compared in feeding trials with lactating cows, most studies report either no difference in milk production and composition or a slight (statistically insignificant) increase in milk production with high cut. Increasing cutting height will unquestionably reduce yields, but based on research, it is unlikely to result in substantial increases in milk production.
What is the correct chop length? The ideal chop length for corn silage is a compromise between what is good for silage fermentation and what is good for the cow. Fine chopping promotes good packing and increases the rate of fermentation in the silo, but fine chopping may result in silage that does not promote adequate chewing when fed to the cow. Extremely coarse chopping may cause problems with fermentation in the silo and can increase sorting when fed to cows. Historically, chop length has been described as the theoretical length of cut (TLC) at which the chopper was set, but TLC is a poor descriptor of actual particle size of the silage. A better approach is to actually measure particle size at the time of chopping with a device such as the Penn State Particle Separator. Corn silage that had not been kernel processed with 3 to 6% of the silage on the top screen and 60 to 65% on the second screen (8 mm hole diameter) of the Penn State Separator was equal or better than more coarse silage based on chewing time, rumen pH, milk fat percentage, and starch digestibility. For processed corn silage, a very wide range in particle sizes (equivalent to approximately 2 to 21% on the top screen) had no effect on chewing time, rumen pH, milk fat, sorting, intake, or digestibility. In that experiment, the processing rolls were set at 1 mm for all chop lengths. As long as the rolls are set properly (i.e., most kernels are physically damaged), setting the chopper so that about 10% of the corn silage is on the top screen is a good guideline. Particle size evaluation should be done when you start chopping so that adjustments can be made.
Should kernel processing be used? The main advantages to proper kernel processing is that corn silage can be chopped coarser without decreasing digestibility of the kernel (starch) and it makes particles more homogenous (makes sorting more difficult). Proper kernel processing is when most of the kernels are physically damaged. The response to kernel processing is a function of the maturity of the corn plant and hybrid. Processing usually increases the nutritional value of mature (or drier) corn silage. On average, corn silage at two-third milk line or more mature that is processed has about 7.5% more available energy than unprocessed corn silage at the same maturity. Processing may decrease the energy value of immature corn silage (less than one-third milk line). The average response to processing for corn between one-third and two-thirds milk line is negligible. Hybrid appears to be one factor affecting the response to kernel processing. Unfortunately, at this time, we do not know which hybrids are likely to respond to kernel processing.
How long should the silage be left undisturbed after filling? Most studies with corn silage show that pH and acid concentrations become stable by 7 to 14 days post-ensiling if the silage is left undisturbed. Yeast and mold counts may require up to 60 days before stabilizing. Opening a silo will probably increase these times. If possible, a silo should be left sealed for at least 14 days. Consider making extra corn silage (enough for 2 to 4 weeks) this fall and storing it so that it can be fed during silo filling next year.