1. Harvest at 30-40% whole plant dry matter (WPDM)
This is the most important information to know for making good corn silage. Bacteria present on corn plants in the field ferment plant sugars contained primarily in the stalk to produce fermentation acids that preserve the corn silage.
To ensure a vigorous and successful bacterial fermentation the dry matter (DM) content of the whole corn plant material at harvest is very important. The proper DM content for optimum fermentation is between 30% and 40%. If corn silage is wetter than 70% moisture (30% DM) excessive fermentation acids can reduce palatability and feed intake. Wetter silage is more likely to result in effluent loss, which is a huge potential environmental concern for Michigan dairy farms.
If corn silage is drier than 40% DM there might not be enough sugars available for adequate fermentation increasing DM losses and resulting in heating at feed-out. In addition, if corn silage is too dry, kernels become hard and starch digestibility is reduced.
Determining the DPDM at the beginning and during harvest is the most critical and important harvest management practice to implement. Dry matter can be determined using a Koster™ moisture tester or microwave oven. A publication about using a microwave for moisture testing can be obtained at: http://ianrpubs.unl.edu/range/g1168.htm.
Kernel milk line has been used in the past as an indicator of when to harvest corn for silage. Kernel milk line is an indicator of kernel maturity but is not a good indicator of whole plant DM.
2. Harvest at chop height of 4 to 6 inches
Some publications suggest chopping at 12 to 16 inches from the ground, which will increase the grain concentration and reduce the concentration of fodder in the silage. Implementing this 12 to 16 inch concept would increase the energy density but decrease the fiber content of the silage.
While this practice might make sense when the price of corn grain greatly exceeds the cost of growing and feeding corn silage, many producers are concerned that dairy cow diets do not contain sufficient fiber and they purchase dry hay or straw to increase dietary fiber.
This doesn’t make sense because corn plant fodder is a good source of fiber. Leaving 12 to 16 inch stalks and leaves containing potentially digestible fiber in the field while purchasing other perhaps less digestible fiber sources is a costly venture. MSU’s recommendation is to harvest corn at 4 to 6 inches for silage.
3. Chop length-theoretical length of cut (TLC) of ¼ to ½ inch
Kernels and cobs need to be broken. To accomplish this, chop length may need to vary between ¼ and ½ inch TLC for choppers without a processor depending on WPDM. A chop length of ¼ inch should be used only for very dry corn plants to ensure that the kernels are nicked. Short chop to length silage will require inclusion of another forage source in the ration for adequate effective fiber. For choppers with a processor a ¾ inch TLC is recommended when WPDM is 30 to 40%. Processing when WPDM is less than 30% may result in mashing of the kernels and stalk and the processor rollers should be backed-off to prevent mashing.