How Many Days Can A Beef Cow Graze An Acre of Corn Stalk Residue?
Residue (leaf and husk) yield is related to grain yield, but 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.
I usually estimate 50% utilization of the leaf and husk by the grazing animal. Therefore, 150 bu 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 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 1200lb 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 AUM's (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 AUM's) per acre for a 1200lb cow or 44 days of grazing (30 days per month x 1.5 AUM's = 44 days of grazing). If one acre would feed a 1200lb cow for 44 days then it would feed a 600lb calf for 88 days.
Higher grain yields provide more AUM and lower yields less. One acre of irrigated corn stalks or grain sorghum stubble will provide approximately 1.5 to 2 AUM of grazing.
Dr. Rick Rasby, Professor of Animal Science
Animal Science, University of Nebraska - Lincoln, Lincoln, NE