Drought-stressed corn does not necessarily represent a complete loss of feed value. As discussed in the companion article on utilizing drought-stressed corn for forage, timely harvest and proper ensiling practices can preserve much of the crop's remaining nutritional value and provide an economical feed resource during dry growing seasons.
However, successfully harvesting drought-stressed corn is only the first step. Environmental stress can also alter plant chemistry, increasing the potential for nitrate accumulation and mycotoxin contamination while creating greater variability in nutrient composition and forage quality. These changes can influence both animal performance and health if the forage is not properly evaluated before feeding.
This article focuses on the feeding management considerations that follow harvest, including how drought affects feed quality, strategies for managing nitrate and aflatoxin risks, and the importance of forage testing when incorporating drought-stressed corn into livestock rations. Understanding these factors allows producers to safely maximize the value of drought-damaged corn while minimizing risks to animal health and productivity.
Nitrate Concerns
Drought-stressed corn may accumulate nitrates, particularly in the lower portion of the stalk. The risk is often greatest when drought conditions are followed by rainfall or when excess nitrogen remains available in the soil. Management practices to reduce nitrate risk include:
- Raising the cutter bar and leaving approximately twelve inches of stalk in the field
- Testing forage when drought stress or high nitrogen fertility conditions are present
- Avoid feeding high-nitrate forage without proper management
- Avoiding non-protein nitrogen supplementation when nitrate concerns exist
Because the fermentation process can reduce nitrate concentrations, testing silage after ensiling provides the most accurate assessment of feeding risk.
Aflatoxin Risk
Hot, dry conditions during pollination increase the risk of Aspergillus flavus infection and subsequent aflatoxin contamination in corn grain. Key considerations for aflatoxin risk include:
- Increased infection pressure during drought and heat stress
- Greater susceptibility of poorly developed or insect-damaged ears
- Limited reduction of aflatoxin concentrations through ensiling
Aflatoxin is highly toxic and can be transferred from feed into milk as aflatoxin M1. Regulatory limits include 20 ppb in dairy cattle feed and 0.5 ppb in milk. Fields with suspected contamination should be tested before feeding.
Feed Value Considerations
Nutrient composition of drought-stressed corn silage is highly dependent on grain development. General trends include:
- Greater grain development results in higher energy concentration.
- Poor pollination reduces starch content and overall energy value.
- Fiber digestibility may vary due to changes in plant maturity and structure.
According to an Iowa State University Beef Center report, drought-stressed corn may retain approximately 70–90% of the energy value of normal corn silage, although considerable variation can occur among fields (Loy, 2012). As a result, visual appraisal alone is insufficient for determining feeding value or market price.
Table 1 presents nutrient composition data from eight fresh corn silage samples collected in South Dakota during the 2012 drought. Energy values ranged from 0.61 to 0.72 Mcal/lb and generally increased with starch concentration.
| Samples | ||||||||
|---|---|---|---|---|---|---|---|---|
| Nutrient* | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Dry Matter (%) | 24.3 | 26.9 | 24.3 | 25.4 | 25 | 25.5 | 26.5 | 26.9 |
| Protein (%DM) | 9.34 | 9.11 | 8.86 | 8.91 | 10.2 | 9.1 | 7.83 | 8.34 |
| ADF (%DM) | 34.1 | 29.7 | 28.4 | 28.9 | 24.8 | 25.3 | 23.7 | 22.8 |
| NDF (%DM) | 55.7 | 50.7 | 48.3 | 47.5 | 43.7 | 46 | 40.2 | 40.6 |
| Lignin (%DM) | 4.43 | 3.28 | 3.34 | 4.05 | 3.24 | 2.6 | 2.72 | 2.6 |
| Starch (%DM) | 4.99 | 8.33 | 9.52 | 13.7 | 14.1 | 20.1 | 28 | 29.6 |
| Sugar (%DM) | 8.67 | 14 | 12.4 | 9.48 | 13.3 | 9.15 | 6.76 | 5.75 |
| Ash (%DM) | 6.5 | 6.18 | 5.71 | 8.85 | 5.98 | 5.83 | 4.72 | 4.76 |
| Nitrates (ppm) | <300 | 1700 | <300 | <300 | 640 | 736 | <300 | <300 |
| NEl (Mcal/lb) | 0.61 | 0.65 | 0.65 | 0.62 | 0.67 | 0.69 | 0.71 | 0.72 |
*Abbreviations: DM (Dry Matter), NDF (Neutral Detergent Fiber), ADF (Acid Detergent Fiber), NEl (Net Energy for lactation).
Conclusion
Drought-stressed corn can remain a valuable forage resource when harvested and stored appropriately. Although yield and grain development are often reduced, drought-damaged silage frequently retains a substantial portion of the energy value found in normal corn silage, particularly when some ear development is present. However, forage quality can vary widely depending on the timing and severity of drought stress.
Successful utilization depends on careful management, including harvesting at the proper moisture content, achieving adequate packing density, and excluding oxygen during storage. Producers should also manage potential risks such as nitrate accumulation and aflatoxin contamination through appropriate testing and harvest practices. Because field conditions can strongly influence both feed quality and safety, drought-stressed corn should be evaluated on a field-by-field basis, with laboratory analyses used to guide ration formulation and pricing decisions. Proper management can help producers maximize feed value while minimizing risk during drought years.
Sources
Loy, D. 2012. Feeding Value of Drought-Damaged Corn Silage for Beef Cattle. Iowa State Beef Center.
