Feed Value
Although some parts of Nebraska have recieved adequate moisture recently, the extremely hot weather experienced this summer will still affect yields of most dryland and some irrigated corn. Silage is often a good way to salvage cattle feed from a corn field that is cut short by drought. Silage made from drought-stricken corn has been shown to be nearly equal in feed value to well-eared corn. The extent of the drought damage determines how this silage will compare with "good" corn silage, however.

In a series of studies conducted at the Northest Research and Extension Center, Concord, the value of drought silage ranged between 70 and 104% of the value of normal silage depending on whether supplemental corn was fed with the silages and type of protein provided. Feeding supplemental corn with drought corn silage in a growing ration increased the feed value (based on feed efficiencies) form 99 to 104% of normal. In other studies conducted at the same center,the value of drought silage was found to be 70 to 79% of normal silage when urea and soybean meal were fed as the source of supplemental protein, respectively. When no protein was provided, drought silage was found to be 98% the value of normal silage in the same study. In this study, the higher protein content most likely offset the lower energy content of the drought silage allowing steers of both groups to perform similarly. In these studies, yields of corn averaged around 10 bu/acre on fields drought silage was harvested from.

In two South Dakota trials conducted in the 70's drought damaged corn silage, containing four to eight bushel of corn/acre and yielding up to 3.5 ton dry matter forage/acre, was found to have feed value similiar to normal corn silage. In the first trial, silage was harvested in mid-August at 70% moisture. In the second trial, silage was harvested at 66% moisture and was full fed with 2 lb of a 32% protein supplement to feedlot steers for nearly 300 days. Daily gains averaged 1.94 lb/day. On the basis of this and other research conducted in Iowa and Missouri, the feed value of drought-silage will most likely average from 75 to 95% the value of normal corn silage, depending upon extent of drought damage. Drought silage gernerally has 10 to 11% crude protein (DM) compared to 8.0% crude protein (DM) for normal corn silage. Much of the extra protein value is in the form of non-protein nitrogen compounds, particularly in growing rations.

Dollar Value
One method of determining the value of drought silage is based upon the price of hay. This method of pricing best fits those operations in which the forage shortage is critical, substitute forage is needed and feed type and nutrient composition is a lesser concern. This pricing method assumes the value of one lb. of alfalfa hay is equivalent to one lb. of corn silage after moisture is corrected for and adjustments in storage and harvesting costs are taken into account.

In operations in which feed type and relative nutrient composition (ie: protein and energy) are of a greater consideration, an alternative pricing system for drought silage should be used and is based upoon the price of normal corn silage. With this method the price of normal corn silage is first determined (Table 1).

For corn standing in the field, the price would be $20.00/ton minus $4.00/ton harvesting charge ($20-$4 = $16.00/ton). To determine drought corn forage price either as green chop or standing in the field, multiply the normal forage price times the relative value of drought silage when compared to the normal silage.

The above formulas are rules of thumb that can be used for pricing normal and drought silage. In NebGuide G74-99 a more detailed pricing method is described, which takes into account the price of harvesting and storing costs, crop residue value and bunker filling and removal costs. The above described pricing method does give fairly close estimates of the silage prices found in the NebGuide, however.

A third method of pricing drought silage is by taking into account the relative value of the protein (based upon the price of soybean meal) and energy or TDN (based upon the price of corn). At respective corn and soybean meal prices of $2.50/bu and $250/ton, the relative values of normal and drought corn silage are $28 and $31/ton. In this case, the value of the drought silage is greater than the value of normal silage, due to its greater protein content. Since the extra protein in drought silage is in the form of non-protein-nitrogen, which may not be as effectively utilized as protein in soybean meal, and since the relative price of corn and soybean meal can vary greatly, this pricing method is generally not used. However, this method does provide an upper limit for pricing drought silage since it will usually give greater value to drought silage than the other methods. Because proper protein and energy values for soybean meal and corn, respectively, are needed, this method also requires considerably more mathematical computation than other methods.

Nitrate Content
Corn plants that have had their growth arrested by drought are more apt to have a high nitrate content than normal corn forage. The heaviest concentration of nitrates is in the stalk of plants. Cutting the stalk at least 12 inches or so above the ground will reduce the nitrate content of the forage in comparison to closer cuttings. Research conducted in 1968 at the Northeast Nebraska Research and Extension Center, found that nitrate levels in corn silage cut about 4 inches above the ground were 1500 ppm, while silage cut at 12 inches above the ground contained nitrate levels of 600 ppm (Table 2).

Conversion of nitrates to nitrites by bacteria during fermentation and heating increases the danger of high-nitrate feeds. Nitrite is much more toxic to cattle than nitrate-nitrogen and usually the cause of death in "nitrate" poisioning. Nitrite content of silage is apt to be higher during the initial fermentation phase, therefore, silage should not be fed until fermentation has stopped, which occurs about 28 days after storage. Ensiling can be a way, however, to make high-nitrate forage a safer feed, since silage often loses 1/3 to 1/2 of its nitrate content once fermentation is complete.

Young animals are much more sensitive to nitrite as compared to mature animals of the same species. However, pregnant animals may lose fetuses because of anoxia (lack of oxygen in the blood) without any apparent long range damage to themselves in nitrite/nitrate poisoning.

Many cattlemen will feed drought-stricken corn as green-chop. If the damaged corn is high in nitrate, certain precautions should be taken with green chop to reduce the risk of livetock losses. If a nitrate analysis is not conducted on the silage or green-chop, then feeding it to a few animals for a couple of days for observance of toxic problems, before offering it to the whole herd, is advisable. Turning a few tester animals in first to screen for nitrates is a good idea if you are going to graze a drought stricken field.

A delay in feeding the corn forage after it is chopped will increase the conversion of nitrates to nitrites by bacterial action. Don't hold green-chop overnight of let it heat or spoil. Chop and feed twice a day, using a relatively coarse cut. Do not feed more than the cattle will eat in a few hours.

The addition of high energy palatable feedstuffs to the ration will offset nitrate toxicity to some extent. The feed should be fed in conjuction with the nitrate feed. If hay is fed instead of grain, cattle may not always eat it if they receive an appreciable amount of green-chopped corn fodder, but consumption of even a pound of good legume hay per head daily is helpful. In regard to supplements, plant proteins would be preferred to urea when high-nitrate rations are fed. Check against the use of water high in nitrate for livestock that are fed high-nitrate feeds. The nitrate in feed and water is additive.

It is best to start cattle on green chop slowly. Toxic troubles are most likely to occur in the first four days. Have the cattle full of other feed when they are first offered high nitrate green-chop. Hay or other feeds will be needed to meet daily feed requirements while the greenchop is being limited. Provide adequated mineral and vitamin A (20,000 to 30,000 IU/head/day) at all times. Nitrate levels above 2,000 ppm (.2%) are considered to be toxic, however, nitrate levels in a ration up to 5,000 ppm have generally been adequately handled by most cattle, when properly adapted.