Two factors influence whether or not there is benefit to feeding cows a protein supplement when grazing cornstalks. Consider the following when determining whether or not the feeding of a protein supplement is needed.
Quality and quantity of forage available
The first factor is the quality and quantity of forage available. The amount of corn, leaves and husks will vary with growing and harvest conditions.
Cattle will select the grain and best quality forage first when initially turned into a field. As cattle continue to graze diet quality will decrease. Once cattle have eaten the available husks and leaves and begin eating more of the stalk, diet quality will go down significantly.
Weathering will deteriorate forage quality. Cool, dry weather conditions in the fall and winter will maintain quality for a longer period of time; while wet, warm, muddy conditions will result in a faster deterioration of leaves and husk.
Cow body condition score at the initiation of grazing
The second factor is cow body condition score at the initiation of grazing. Recent research at the University of Nebraska indicates that mature, spring calving cows in a body condition score 5 or better do not need supplemental protein or energy when grazing targets removal of half of the leaves and husk based on corn yield. See the 2012 Nebraska Beef Report Supplementing Gestating Beef Cows Grazing Cornstalk Residue (PDF 148KB) for more information.
Plan to supplement cows with salt and mineral. Bred two-year-old heifers in their third trimester as well as lactating cows will have higher nutrient requirements. These will need both protein and energy supplementation to meet their nutrient requirements. Spring calving cows in a body condition score less than 5 would likely benefit from protein supplementation.