Stretching Corn Silage Supplies

Dr. Bill Weiss, Dairy Specialist, Ohio State University 

In many areas of Ohio, corn silage yields were much lower than average last year because of the drought. Forage supplies are tight and hay prices are extremely high, but on the bright side, first cutting of alfalfa is approaching rapidly. Diets with less than typical concentrations of corn silage can be fed safely. The following steps should be followed if forage supply is limited.

1. Determine current corn silage inventory.

Example. 1000 tons of corn silage was harvested last September. The silage is fed to 150 lactating cows at the rate of 40 lbs/day. Since harvest, 660 tons have been fed (150 cows x 40 lbs x 220 days) leaving 340 tons.

2. Determine maximum amount of corn silage that can be fed based on available inventory.

Example (continued). As of May 1, 340 tons of corn silage is available. At the current feeding rate (40 lb X 150 cows = 3 tons/day), the remaining corn silage will last about 113 days (340 tons remaining divided by 3 tons fed/day). New crop corn silage will be available on October 1 (150 days). The maximum amount of corn silage that can be fed is 340 tons divided by 150 days = 2.3 tons/day or about 30 lb/head/day. To ensure adequate supply, reduce that value by 10%. The maximum amount of corn silage that should be fed is 27 lb/day per cow.

3. If inventory is not adequate based on current feeding rate, immediately reduce the amount fed to that value calculated in step 2. Changing now, rather than later, will reduce the magnitude of the change.

4. If the amount of corn silage fed must be reduced, replace it with logical alternatives.

Alternative feeds

In typical diets, forage is the major source of dietary fiber (expressed as neutral detergent fiber, NDF) and effective fiber (fiber that stimulates chewing and rumination). Several byproduct feeds have concentrations of NDF equal to or greater than that found in typical forages (Table 1) and can be used to provide NDF. Byproducts, with the exception of whole cottonseed, however, are not good sources of effective NDF.

Feeding diets with inadequate concentrations of NDF and effective NDF is a substantial risk factor for ruminal acidosis. Diets with low concentrations of NDF typically have high concentrations of nonfiber carbohydrates (NFC). In the rumen, NDF usually ferments slower and less extensively than NFC, resulting in less acid production and a higher rumen pH. Effective NDF is important because it stimulates chewing and salivation. Saliva is an excellent buffer and helps maintain rumen pH. When low forage diets are fed, dietary concentrations of NDF, effective NDF, and NFC must be adjusted properly to maintain rumen health.

Table 1. Average concentrations of NDF and crude protein (CP) in common byproducts.

Options when corn silage is limited

1. Replace corn silage with hay crop forages. New crop grass and legumes will be available in Ohio in mid to late May. If these forages will be available, increase their concentrations in the diet and reduce the amount of corn silage. The diet must be reformulated (especially with respect to protein and minerals) when hay crops replace corn silage. If increased feeding of hay crops during the summer will mean that the inventory of hay crops will not be adequate for winter feeding, more acres of corn silage should be planted and chopped.

2. Replace corn silage with byproducts. When low forage diets are fed, dietary concentrations of NDF must be increased and concentrations of NFC must be reduced. Typical diets in Ohio have NDF concentrations in the 27 to 30% range and NFC concentrations in the 38 to 41% range. Low forage diets should contain at least 32% NDF and no more than 38% NFC. Several experiments have shown that diets with 17 to 18% of the dry matter (DM) as forage NDF can be fed to cows without problems as long as the concentration of total NDF in the diet is increased to dilute out NFC and reduce acid production in the rumen. As forage is removed from the diet, it must be replaced with high fiber byproducts, not by starchy feeds such as corn grain. A general rule is for every 1 percentage unit forage NDF is reduced below typical values (approximately 21% of diet DM), total diet NDF should be increased by 2 percentage units. For example, if the amount of forage in a diet is reduced by 2.5 lb/day of DM, the amount of forage NDF fed will be reduced by 1.1 lb (assuming the forage has 45% NDF). To account for a loss in effective NDF, total NDF intake should be increased by 1.1 x 2 = 2.2 lb/day. Soyhulls have about 60% NDF; therefore, 3.7 lb of soyhull DM would be needed to provide 2.2 lb of NDF (i.e., 2.2/0.6 = 3.7). In this example, 2.5 lb of forage and 1.2 lb of corn grain would be replaced with 3.7 lb of soyhulls (all amounts are on a DM basis). Depending on the protein content of the forage, some changes in soybean meal might also be needed. For moderately low forage diets, replacing a portion of the forage and corn grain with a high fiber byproduct may be all that is necessary. The choice of which byproduct to use should be based on cost of the nutrients provided by the feed (see Cost of Nutrients article by Normand St. Pierre) and the need for supplemental crude protein.

If forage supply is severely limited (< 17% of diet DM as forage NDF), the approach outlined above may not be adequate. Dietary NDF concentrations must be increased to dilute NFC as described above and additional sources of effective NDF might also be needed. The only byproduct commonly available in Ohio that is a good source of effective NDF is whole linted cottonseed. Diets with 10 to 15% (DM basis) whole cottonseed can be fed without problems. The minimum amount of cottonseed that should be fed is based on the amount of forage NDF provided in the diet. A general guideline is that forage NDF plus the NDF from cottonseed should equal or exceed 17% of diet DM. For example, if forage NDF is 14%, at least 3 percentage units of dietary NDF should come from whole cottonseed. The minimum amount of cottonseed in the diet equals 3 divided by 0.47 (NDF concentration of cottonseed) = 6.4% of diet DM. Total dietary NDF should be increased from 27% (minimum concentration for adequate forage diets) to about 35% (i.e., 21% forage NDF (requirement with adequate forage diets) minus 17 (amount of NDF from forage and cottonseed in this example) times 2). For this example, the diet would consist of 35% forage (assuming the forage is 40% NDF), 6.4% whole cottonseed, and 58.6% concentrate mix that contains 30% NDF.