Mechanical Processing of Corn Silage

There have been several excellent reviews published recently on the role of processed corn silage in dairy rations. Processing corn silage refers to passing the entire plant through rollers either before or after ensiling. Processed corn silage has been shown to improve starch and fibre digestion, improve ensiling characteristics, reduce dry matter losses during ensiling and increase milk production. The following article highlights the key points discussed in the reviews. Copies of the complete reviews (Johnson et al, Journal of Dairy Science, 1999; Harrison et al, Silage: Field to Feedbunk, 1997; Satter et al, Minnesota Forage Conference, 1999) are available from my office for those of you interested in more information.
The use of mechanical processing systems for corn silage is growing rapidly in North America. Several factors have contributed to this interest: rising grain prices, a trend towards longer TLC (theoretical length of cut) which reduces kernel damage, and a rapid dry down of kernels due to climatic change.
Mechanical processing can be done before ensiling with a processor mounted on a forage harvester or by a stationary roller mill located at or near the silo. The stationary roller mill can also be used to process the silage after ensiling. The most popular system is the processor attached to the forage chopper. This unit consists of two counter-rotating rolls positioned between the cutter head and blower. This results in crushing of the grain as well as crushing and shearing of the cob and stem. Rollers are typically set for 1 - 5 cm clearance with the lower clearance used for more mature corn. Stationary roller mills crack the grain kernel but cause little, if any, shredding of the stem fraction.
Mechanical processing on the forage harvester reduces the particle size of corn silage by 15 to 30% and reduces the number of undamaged corn kernels from about 20% to less than 5% of total kernels. Processing before ensiling has been shown to decrease particle size to a greater extent than does processing with a stationary mill post-ensiling. Because the particle size of silage is decreased with processing, it is important to increase the TLC at harvest to provide the necessary effective fibre to the cow. Research has determined that adequate effective fibre can be obtained, without affecting compaction in the silo, by increasing the TLC to ¾ inch. Silage fermentation characteristics (pH, lactate, acetate), % dry matter, and dry matter loss are affected by mechanical processing. Dry matter loss is lower for processed silage. Results for fermentation characteristics are variable and appear to be dependent on maturity at harvest. The Wisconsin State University Dairy/Forage Facility evaluated the effect of processing corn silage cut at three maturities - hard dough(23% DM), 1/3 milk line (28% DM), and 2/3 milk line with a killing frost (30% DM). Processing had little or no effect on pH decline through day 10 post-ensiling for the dough and 1/3 milk line silages, however, the 2/3 milk line silage was observed to ferment more quickly and had a lower pH by day 10 after ensiling.
Milk production of cows fed processed corn silage is typically about one pound higher than for cows fed unprocessed silage. Larger increases have also been reported. A 1998 Wisconsin trial indicated that cows fed processed silage ate 1.5 pounds more dry matter per day and produced 2.5 lbs. more milk and 3.5 lbs. more FCM per day than cows fed unprocessed silage. Increases in milk production are due primarily to improvements in starch and fibre digestibility. A consistent improvement in milk protein yield has also been observed.
The most important question asked by dairy producers is "Does it pay?" This can only be answered on a farm by farm basis after considering factors such as number of cows in milk, amount of corn silage fed, and the maturity at which the silage was or will be harvested. Researchers at Washington State University found the economic benefit of mechanically processed corn silage ranged from $5 to $100 per cow per year when farm size, maturity of corn silage, milk price, and feed prices vary.
A simplistic method for estimating the potential return from processing has been outlined by Dr. Satter. The following example uses Manitoba milk and equipment prices
Increased milk production 1 lb./day
Value of extra milk over 305 days $67
Total equipment cost $15,000
Cost/year (depreciated over 5 years) $3,000
Number of lactations needed to pay for equipment 45
Opportunity cost ($/ton) for custom harvesting (silage DMI=17 lbs/day) $9.00
Complex computer software is available to accurately determine the economic impact of processing corn silage as well as other management changes.