How Many Days Can A Beef Cow Graze An Acre of Corn Stalk Residue?
NoNoel Mues, Extension Educator
University of Nebraska-Lincoln Extension
Previously we have discussed the many benefits that corn stalks have as winter feed and how you manage grazing of stalks can have a big effect on its success.
It may be of interest to you to know how to calculate the number of days that a beef cow can graze an acre of corn stalk residue. Then you must make sure you have enough acres so your stocking level can be light enough so cattle can select just the higher quality plant parts to eat. And whenever the grain and husks are gone you can move your cows to a fresh field.
Residue (leaf and husk) yield is related to grain yield, but corn hybrids obviously vary in this relationship. With high producing corn (irrigated or with ample rainfall) there will be about 16 lb dry leaf and husk per bushel corn yield.
Some residue disappears by trampling and other factors. We usually estimate 50% utilization of the leaf and husk by the grazing animal. Therefore, 150 bu of corn produces 2400 lb leaf and husk per acre on a dry matter basis and 1200 lb (50% of the total 2,400 lb) of husk and leaf on a dry matter basis are available for the animal to consume. This is equivalent to about 1.76 AUM (1200 lb of husk and leaf per acre at 50% use/680 lb of feed per AUM).
One Animal Unit Month (AUM) is the amount of forage required to sustain a 1,000 pound cow or equivalent for one month and it has been determined that a 1,000 pound cow will consume 680 pounds of dry matter monthly.
A 1200 lb cow is 1.2 AU and would consume 816 (680 lb x 1.2AU) pounds of forage dry matter per month. If the corn yield was 150 bu per acre and that yield produces 2400 lb of husk and leaf per acre on a dry matter basis and 50% of the husk and leaf are consumed, then this residue field would provide 1.5 AUMís (1200 lb of husk and leaf on a dry matter basis per acre/816 lb of forage per month for a 1200 lb cow = 1.47 AUMís) per acre for a 1200 lb cow or 44 days of grazing (30 days per month x 1.5 AUMís = 44 days of grazing).
If one acre would feed a 1200 lb cow for 44 days then it would feed a 600 lb calf for 88 days. Higher grain yields provide more AUMís and lower grain yields less AUMís. One acre of irrigated corn stalks or grain sorghum stubble will provide approximately 1.5 to 2 AUM of grazing.
Rick Rasby, UNL Professor of Animal Science
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