Effects of Drought Conditions on Commonly Fed Forages

W. P. Weiss, Department of Dairy Science, Ohio Agricultural Research and Development Center, Wooster, and W. L. Shockey, Center for Agriculture, Natural Resources, and Community Development, WVU Extension Service, Preston County

8/1999

Corn Plants

  1. Ensiled drought-stressed corn silage is a good feed if supplemented properly.
  2. Dry matter yield and energy yield per acre will be lower than that of normal corn silage.
  3. Drought-stressed corn is usually higher in crude protein and lower in energy.
  4. Type of crude protein is also different. Normal corn silage has about 5% true protein and 3% nonprotein nitrogen on a dry matter basis (DMB). Drought-stressed corn silage may have about 5% true protein and 7% nonprotein nitrogen, DMB. This may limit the amount of added nonprotein nitrogen (NPN) the cow can use efficiently.
  5. The biggest concern is energy. You must feed more grain with drought-stressed corn silage because of its low energy value. A general rule--12 parts wet drought-stressed silage plus 1 part corn grain is equal to normal corn silage. Energy content of drought-stressed corn may vary tremendously so first have it analyzed and then determine how much grain is needed.

Example:

A test shows that drought-stressed corn silage has an energy value of 60% total digestible nutrients (TDN). Normal corn silage has an energy value of 70% TDN. Corn grain has an energy value of 87% TDN. If your ration had 50 pounds of non-drought-stressed corn silage and the corn silage was 40% dry matter, you would be supplying 14 pounds of TDN. Drought-stressed corn silage would provide only 12 pounds of TDN. To make up the additional 2 pounds of TDN, you would need to feed 46.5 pounds of corn silage and 3.5 pounds of corn grain.

  1. Because drought-stress conditions can vary from farm to farm, it is recommended that you test all drought-stressed corn silage so that feed is used most efficiently.

Alfalfa

  1. Drought-stressed alfalfa yields are lower, but quality is higher compared to non-drought-stressed alfalfa harvested at the same stage of maturity.
  2. Let alfalfa stand until mid- to full-bloom stage to gain maximum dry matter yields. Once the plant has reached full bloom, dry matter yield will not increase, even if rain occurs. Harvest no later than full-bloom stage of growth.

Grasses

  1. Like drought-stressed alfalfa, yields are lower.
  2. Drought-stressed grasses contain higher levels of fiber and lower levels of protein and energy. To maximize dry matter yields, drought-stressed grasses should be harvested at the head stage of growth. Little dry matter increase is observed after the heading stage, but quality begins to decrease rapidly.
  3. As with all drought-stressed forages, analyze grasses before feeding.

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