FEEDING DROUGHT-STRESSED CORN SILAGE TO BEEF CATTLE Dan B. Faulkner, UIUC Extension Beef Specialist as edited by Paul Walker, Animal Scientist, Illinois State University

DURING DROUGHT CONDITIONS many producers will seek ways to get some economic return from drought-damaged corn. Feeding corn to livestock may be the best alternative use for this material. If a producer does not have the facilities or livestock to use the drought-stressed corn, it may be possible to sell the corn to someone who can use the feed. HARVESTING Ensiling is the preferred method of harvesting drought silage. Proper ensiling will reduce the nitrate level by 40 to 60 percent. When ensiling corn, it is important to wait until the plant dries to the correct moisture level and is no longer green. The correct moisture content will vary with the type of storage structure. For example: Bunker or bag storage = 30 percent dry matter (DM) Conventional silo = 35 to 40 percent DM Oxygen-limiting structure = 40 to 50 percent DM Because the silage will be higher than normal in protein, it may not be beneficial to add nonprotein nitrogen (urea or anhydrous). However, it may be beneficial to add a bacterial additive due to the possibility of less than optimum fermentation conditions. It is important to wait 4 weeks for fermentation to be complete prior to feeding the silage. The cattle can be selffed out of bag storage if equipment and facilities are not available. Greenchopping is a less desirable option than silage, but it may be used in an emergency. Nitrate levels are a concern with greenchopping (see Nitrate Levels section). The risks can be minimized both by introducing the feed gradually so that the animal can adapt and by cutting the corn high (8-12 inches off of the ground) to avoid the nitrates concentrated in the lower part of the stalk. Pasturing the corn is also an option in an emergency. Again, a producer must be concerned with nitrates in the lower part of the plant. To minimize risk, the cattle should not be hungry when first introduced to the cornfield. Having hay available and not forcing the cattle to graze the lower part of the stalk could also reduce the risk. Limit the cattle to a small area with an electric fence to minimize waste.

Haying the corn plants is quite difficult because of drying problems. It is important to crush the stalk to assist drying. Nitrate levels can also be a problem because the level will not change after harvest. It may be beneficial to grind this hay to get the cows to consume the larger stalks. PRICING The weight and dry matter (DM) content of the corn will determine its value. Determine an exact value by weighing the corn and doing a DM analysis. When grazing corn or when it is not possible to weigh the corn, it may be necessary to estimate the amount of standing corn in a field. Drought corn with no ear will generally produce from 1 to 1.5 tons of 35 percent corn silage/A for every foot that is harvested. Short corn may produce 1 ton and tall corn may produce 1.5 tons/foot harvested/A. For stressed corn with grain, you can expect to harvest 1 ton of silage/A for each 5 bu corn grain/A. For example, if you expect a grain yield of 50 bu/A, you can expect 10 tons/A of 30 percent DM silage. A quick method of calculating the maximum value of drought corn silage is as follows: Step 1.

Calculate the value of normal corn silage using the equation (cost/bu of corn x 6) + harvesting costs = value/ton of 30 percent DM silage. The harvesting cost may vary from $6 to $10/ton depending on the yield and type of equipment used. The harvesting costs should not be included if the buyer harvests the corn. If corn is $3.50/bu and it costs $6/ton to harvest silage, the value of normal corn silage would be $27.

($3.50/bu x 6) + $6 = $27/ton silage Step 2.

Test the stressed silage to determine feed value or use an average value of 80 percent of normal silage. The value would be $21/ton for silage worth 80 percent that of normal corn silage.

$27/ton x 80 percent = $21/ton stressed silage Step 3.

Adjust the value of the corn for the DM content (if it is known) by multiplying the price/ton of 30 percent DM corn by the actual percent DM and dividing by 30 percent. This will work for both silage and corn hay. If the DM content of corn hay is 90 percent, then it is worth $63/ton. If the DM content of silage is 40 percent, then it is worth $28/ton.

($21/ton x 90 percent DM)/30 percent DM = $63/ton corn harvested as hay ($21/ton x 40 percent DM)/30 percent DM = $28/ton 40 percent DM corn silage

NITRATE LEVELS The nitrate levels that can be fed before you can expect problems are listed below. Higher levels have been successfully fed in some cases, but there is risk associated with this practice. Nitrate content percent (DM basis)

Comment

0.0 to 0.44

This level is considered safe to feed under all conditions.

0.44 to 0.66

This level is safe to feed to nonpregnant animals under all conditions. It may be best to limit its use for pregnant animals to 50 percent of the total ration on a dry basis.

0.66 to 0.88

Feeds can be safely fed if limited to 50 percent of the total DM in the ration

0.88 to 1.54

Limit feeds to about 35 to 40 percent of the total DM in the ration. Do not use feeds containing over 0.88 percent nitrate for pregnant animals.

1.54 to 1.76

Limit feeds to 25 percent of total DM in the ration. Do not use for pregnant animals.

over 1.76

These feeds are potentially toxic. Do not feed.

To convert other methods of reporting nitrate to nitrate, multiply potassium nitrate by 0.6 and nitrate nitrogen by 4.4. To convert parts per million (ppm) to percent, divide by 10,000 (i.e., 1,500 ppm is 0.15 percent). Cattle grazing corn or consuming green chopped corn can experience problems with nitrate toxicity. Testing these feeds is of limited value because the concentration will vary with time and environmental changes. Nitrate levels are lowest on the afternoons of sunny days. They are extremely high following a rain and should be avoided at that time. Obviously, there is some risk associated with feeding high nitrate feeds. With the shortage of other feeds and the availability of large quantities of drought-damaged corn, producers may need to accept this risk. Minimize the risk by following these guidelines.

FEEDING VALUE The nutrient content of the silage should also be analyzed. Drought silage will generally have 80 percent (65 to 95 percent) the energy value of normal corn silage. A laboratory test for acid detergent fiber (ADF) will reflect the altered energy content, the key nutrient variable. Total digestible nutrients (TDN) is a common measure of energy that can be calculated from ADF as follows: TDN = 87.84 - (0.7 x percent ADF) The protein level of drought silages is generally higher than normal silage. Unfortunately, much of this protein is in the form of nonprotein nitrogen (NPN). It can be used by cows and feedlot cattle, but it is of limited use for young cattle (under 600 lb.) and dairy cattle. The calcium and phosphorus levels of drought silage may be lower than normal silage. I recommend that you analyze for these minerals and supplement accordingly. General feeding recommendations for drought silage vary with the type of cattle. It is important to supplement all types of cattle with calcium, phosphorus, vitamin A, trace minerals, and salt. Drought silage is generally adequate in protein and energy for beef cows in all stages of production. Stocker cattle (including replacement heifers) can use drought silage. A summary of seven studies indicates that feeding drought silage results in slightly less performance with stocker cattle (Table 1). Two studies indicate that corn can be added to drought silage, but increases in performance may be less than expected due to negative associative effects (Table 2). The research also showed that soybean meal supplementation improved performance 0.3 lb/day on drought silage and 0.2 lb/day on normal silage (Table 3). This was observed despite the higher protein content of the drought silage. For this reason, supplement drought silage with natural protein and do not add urea or ammonia at harvest. Finishing cattle can use drought silage as a roughage source at 10 to 20 percent of the diet DM. Avoid intermediate mixtures of grain and drought-damaged silage once the cattle are adapted to the finishing diet. These mixtures will not give the expected performance due to negative associative effects. It may be cattle longer on a drought silage diet prior to the finishing phase if a producer wants to use more drought silage.

Table 1. Feeding Value of Drought-Damaged Silage (Seven Trial Summary)a Corn silage Control

Droughta

Standard error

Number of cattle 170 262 Average daily gain (lb/d) 2.17 1.97 Dry matter intake (lb/d) 16.13 15.51 Feed/gain 7.70 8.12 Metabolizable energy value (mcal/lb) 1.12 1.10 Net energy gain (mcal/lb) 0.46 0.45 a Michigan, 1988. b Corn yield in the drought-damaged silage was less than 20 bu/A in all seven trials.

0.20 1.16 0.72 0.06 0.044

Table 2. Comparison of Drought-Damaged and Normal Corn Silages

Item Number of steers 1968-1969a 1969b TOTAL Daily gain (lb) 1968-1969a 1969b Average

Drought silage No 6 lb corn corn/head daily 24 20 44

1.52 2.24 1.88

Feed/lb gain (DM) 1968-1969a 10.3 b 1969 7.8 Average 9.0 a Calves fed 91 days. b Light yearlings fed 63 days.

24 20 44

1.70 3.01 2.36

10.1 6.3 8.2

Normal silage No 6 lb corn corn/head daily 24 20 44

1.46 2.65 2.06

11.2 7.0 9.1

24 20 44

1.87 2.80 2.34

10.0 6.6 8.3

Table 3. Comparison of Drought-Damaged and Normal Corn Silagesa Drought silage No Item protein Number of steersb 28 Initial wt. (lb) 420 Daily gain (lb) 1.08 Feed intake (lb DM) 13.2 Feed/lb gain (lb DM) 12.4 a Nebraska, 1976. b Calves fed 190 days.

Urea 28 424 1.18 14.0 11.9

Normal silage Soybean meal 28 425 1.47 14.4 9.8

No protein 9 412 1.03 12.3 11.9

Urea 9 399 1.64 13.6 8.3

Soybean meal 9 400 1.81 13.9 7.7

Issued in furtherance of Cooperative Extension work, Acts of Congress of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, DONALD L. UCHTMANN, Acting Director, Cooperative Extension Service, University of Illinois at Urbana-Champaign. The Illinois Cooperative Extension Service provides equal opportunities in programs and employment. References to commercial products or trade names are for educational purposes only. No discrimination is intended and no endorsement by the Cooperative Extension Service is implied for specific products.