Feeding drought-stressed corn silage to the dairy herd

Faith Cullens, Michigan State University Extension - July 30, 2012

Harvesting and feeding drought stressed corn silage can be a challenge, but for many producers it is necessary to feed their cattle.

With most of Michigan in some state of drought (moderate, severe and extreme) or abnormally dry according to the July 24, 2012 Drought Monitor, both livestock and crop producers are beginning to wonder what will come of their corn crop.

Dairy producers need forage fiber for their herd’s diet. In most cases, harvesting corn silage from plants that produced little to no grain is still a cost effective way to feed the animals. For the crop producer, harvesting corn grain from severely drought stressed corn might not be profitable. This could be an opportunity for livestock producers to have a supply of low-starch corn silage to feed their animals. Be sure to check with the crop insurance agent to determine if and when the crop can be harvested as silage before harvesting.

In evaluating when to harvest drought stressed corn silage, moisture is the key. The whole plant moisture should be at 60-68 percent at harvest for ideal fermentation. Dann Bolinger, a Dairy Specialist with DuPont Pioneer says that what little harvest activity that has already occurred has often proven ill-advised as the plants were generally much wetter than thought. Dead leaves provide no good way for plants to dry down since evaporative transpiration via leaf stomates is no longer a functional mechanism. Stalks are retaining moisture extremely well. Mowing and wilting of plants that are too short to feed into a chopper has been implemented in some instances to facilitate functional harvest and enhanced drying of the leafless stalks to an appropriate dry matter content for ensiling, explains Bolinger. This practice introduces significant soil into the forage not only increasing ash content, but introducing Bacillus and Clostridia bacteria further increasing the risk of an undesirable fermentation - which is already at risk due to the drought condition itself.

Ensiling drought stressed corn silage is the best way to reduce potentially toxic nitrates that accumulate in the plant. Nitrate levels can be reduced 20-66 percent by ensiling. Additionally, harvesting corn 12 inches above the ground will reduce nitrates in the harvested feed, although this will reduce total forage yield (see Table 1 below). Nitrates accumulate in the plant if nitrogen fertilizers (or manure) were used and if there is an interference of normal plant growth, such as drought conditions. In addition, rain on drought stressed corn will cause the plant to quickly take up any nitrates that were left in the soil. When the plant is harvested and fed, ruminants such as dairy cattle, reduce the nitrates to nitrites which are absorbed and cause a decreased ability of the blood to carry oxygen. Symptoms of nitrate toxicity include increased pulse rate, labored breathing, staggered gate, trembling, weakness, blindness, and death.

**Table 1. Nitrate concentrations in drought stressed corn**
Plant part	ppm of NO₃-N
Leaves	64
Ears	17
Top 1/3 stalk	153
Mid 1/3 stalk	803
Bottom 1/3 stalk	5524

Walsh and Schulte. 1970. Soils Dept., Univ. of Wisconsin

It is essential to test corn silage nitrate levels before feeding. Most commercial laboratories offer nitrate testing for $15/sample or less. Laboratories may report nitrates a few different ways. The equations below can be used to convert to nitrate nitrogen:

Nitrate (NO₃) x 0.23 = nitrate nitrogen
Potassium Nitrate (KNO₃) x 0.14 = nitrate nitrogen
Sodium Nitrate (NaNO₃) x 0.16 = nitrate nitrogen

Feeding guidelines for dairy cattle is to keep nitrate levels below 0.4 percent of the total ration and to be extra cautious with pregnant animals. More specific feeding guides for nitrate nitrogen containing feeds are listed in Table 2.

**Table 2. Feeding guidelines of nitrate containing feeds.**
NO₃-N (percent DM)	NO₃-N ppm	NO₃(percent DM)	Guideline
0.0-0.1	0-1000	0.0-0.44	Safe
0.1-0.2	1000-2000	0.44-0.88	OK to gradually introduce, limit to 50 percent for pregnant animals
0.2-0.34	2000-3400	.88-1.5	Limit silage to 50 percent of total ration dry matter. Do not feed to pregnant animals
0.34-0.4	3400-4000	1.5-1.8	Limit silage to 25 percent of total ration dry matter. Do not feed to pregnant animals
>0.4	>4000	>1.8	Potentially toxic, not recommended to feed

If ensiling drought stressed corn silage in upright silos, be extra cautious about the nitrogen dioxide produced during fermentation. Nitrogen dioxide will be produced within 2 hours of ensiling the feed and can remain for 2-3 weeks. Concentrations as low as 25 ppm are invisible, odorless and toxic to humans. At higher concentrations, the gas is yellowish brown and smells like bleach. If it is necessary to enter a silo before 3 weeks of fermentation, run the blower fan for at least 30 minutes prior to entry and leave it running while inside. Using a self-contained breathing apparatus is highly recommended.

Harvesting and feeding drought stressed corn silage can be a challenge, but for many producers it is necessary to feed their cattle and can be done effectively if managed correctly.

Additional information:

MSU Extension’s Drought Resources

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