Buckeye Dairy News: Volume 6 Issue 5
Harvesting and Storing Corn Silage
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.
Forage Inventory Needs for Dairy Farms
Dr. Bill Weiss, Dairy Nutrition Specialist, Ohio State University
The amount of forage eaten by a lactating dairy cow is a function of dry matter (DM) intake and the concentration of forage in the diet. The DM intake can be accurately estimated for a herd, but the concentration of forage in the diet depends on economics, nutrient content of forages and other ingredients, and production and health goals of individual farms. The values presented below are for an 'average' farm and should be adjusted for specific situations.
Table 1. Expected dry matter (DM) intake and annual forage DM needed (tons) for lactating cows at different milk yields (lb/day per lactating cow).% of Dietary DM that is a Specific Forage
Milk YieldDM Intake10%20%30%40% Holstein cows(lb/day)(tons of forage DM needed per 365 days per lactating cow1) 604126.96.36.199.8 805188.8.131.52.3 1006184.108.40.206.9 Jersey cows 403220.127.116.11.8 50318.104.22.168.1 60422.214.171.124.5
1Assumes 10% shrink during storage and feeding and to account for feed refusals. In some situations, shrink could be as much as 20%.
To calculate the amount of a specific forage needed by the lactating herd, the forage numbers in the table should be multiplied by the average number of lactating cows in the herd. For example, if a Holstein herd averages 100 cows that are being milked, average production is 70 lb/day (average for only lactating cows) and the diet contains 40% corn silage (DM basis), 100 cows x 4.05 (average of 3.8 and 4.3 in the table) = 405 tons of corn silage DM is needed to feed the lactating cows for the year. Divide that number by the proportion of DM in the silage to obtain the amount of as-fed silage needed. For example, if the silage averages 35% DM, 405 tons/0.35 = 1157 tons of as-fed corn silage will be needed for the lactating cows.
If the forages fed to lactating cows are also fed to dry cows and heifers, those amounts need to be added. Expected DM intake for a dry Holstein cow is 30 lb/day and 22 lb/day for a dry Jersey cow. The amount of lactating cow forage needed by dry cows = DM intake x the expected concentration of lactating cow forage in the dry cow diet x the average number of days cows are dry x average number of dry cows. For example, if the dry cow diet is expected to be 25% corn silage (same silage as fed to lactating cows), the dry period averages 60 days, and on average you have 15 dry cows, the corn silage needed by dry cows (Holstein herd) would be 30 x 0.25 x 60 x 15 = 6750 lb (3.4 tons). That value should be adjusted for shrink (10%) and added to the number obtained for the lactating cows. On average, DM intake will be 2.2 to 2.3% of body weight for a growing heifer that is gaining at an appropriate rate. Therefore, on average (assuming a normal distribution of ages), a herd of growing Holstein heifers will consume about 16 lb/day of DM (11 lb/day for a Jersey heifer herd). Multiplying the appropriate number by the concentration of lactating cow forage in the diet and by the number of heifers and 365 will equal the amount of lactating cow forage fed to growing heifers. For example, a Holstein herd averages 100 heifers and the diet is 20% corn silage (same silage as fed to lactating cows), the corn silage needed for heifers will be 16 x 0.20 x 100 x 365 = 58.4 tons of DM. After adjusting for shrink (10%), the amount needed is 64.2 tons/year.
In summary, the amount of a specific forage needed for lactating cows is calculated using numbers in Table 1. The amount (if any) of that forage fed to dry cows and growing heifers is calculated and added to the lactating cow number. The sum equals the amount of a specific forage needed by the farm for a year. The actual forage needed by specific farms could be as much as 10% higher.
Getting that Last Cutting of Alfalf
Dr. Mark Sulc, Forage Specialist, Ohio State University
Early September is ideal for taking that last yearly cutting of alfalfa. The timing of this cutting can be very important to the long-term health of the stand. Let's review what is known about fall cutting management of alfalfa.
It is best for alfalfa to not be cut during the 5 to 6 week period before a killing frost. During this critical period, cold resistance and energy reserves for winter survival are built up. A killing frost for alfalfa occurs when temperatures drop to 25oF or less for several hours. So the period from mid-September through October is the critical fall rest period in our region. Harvesting during this period disrupts accumulation of energy reserves and development of cold hardiness.
Producers often harvest alfalfa during the critical fall period despite the increased risk of winter injury. Research shows that often the tonnage gained by cutting during the critical fall period is lost in the first cutting the following year. Plus, there is the increased risk of winter injury and ultimately shorter stand life by stressing alfalfa in this way.
This year, rainy weather has delayed cutting schedules throughout the growing season, pushing back the time when the crop will be ready for a last harvest. The tonnage expected from a fall cutting and the need for the forage should be high before considering a cutting during the critical fall period.
When harvesting alfalfa during the critical fall period, several factors can moderate the risk of winter injury:
- Young, healthy stands are less susceptible to winter injury from fall harvesting than older stands. On the other hand, more future production potential is lost if a younger stand is injured from fall cutting.
- Forages in well-drained soils will be at lower risk of injury than those with marginal drainage. Fall cutting should not be attempted on soils prone to heaving! Removal of the topgrowth cover increases the potential for heaving injury.
- Length of harvest interval during the growing season is often more important than the actual date of fall cutting. Making a 3rd cutting during the fall is less risky than making a 4th cutting in the fall, because a 3-cut schedule allows longer intervals for plant recovery between cuttings compared with a 4-cut schedule. Likewise, a growth interval of 45 days BEFORE a fall harvest will reduce the risk of injury compared with a pre-harvest growth interval of 30 days. The longer growth period allows more energy buildup before the fall harvest, lessening the amount of energy reserves needing to be built up after harvest.
- Fields with optimal soil fertility levels (pH, P, and K) are at less risk than where fertility levels are lower.
- Disease resistant and winter hardy varieties lessen the risk of injury from fall cutting.
- Alfalfa that was not under stress during the summer will be at lower risk. Any stress (wet soils, potato leafhopper injury, etc.) that weakened the crop during the year can increase the risk of damage from fall cutting. This is the case in many of our alfalfa fields this year.
Cutting AFTER a killing frost (25oF for several hours) in late October or early November can be an option for well-drained soils. Leave a 6-inch stubble after late fall cutting. Cutting this late in the year prevents regrowth that burns up energy reserves; however, late removal of plant cover increases the risk of frost heaving! Fall cutting should not be practiced on soils prone to heaving.