Research showing less value in grazing corn residue
November 7, 2013
Rising pasture rent levels and shrinking pasture acres are giving beef producers greater reason to graze corn stalks. However, today's typical corn residue feed value level isn't testing as high as it used to, and beef producers should take steps to validate the nutritional level of grazed residue.
Pike County Ohio State University Extension Education Agriculture and Natural Resources Educator, Jeff Fisher indicates that older publications referring to crude protein and TDN (total digestible nutrient) levels of corn residue are likely to rate those levels higher than what's actually found in most of today's harvested corn fields.
"In the past, analyses of corn residue for grain value showed protein levels as high as 8 to 8.5 percent," Fisher says. "Newer corn hybrids, designed to accelerate yield, are showing average protein levels at 5.5 to 6 percent. In developing a corn residue grazing plan, it's also important to recognize that today's combines are more efficient at capturing corn ears than they used to be and there's probably less grain in today's corn field for cattle to glean."
The proportion of corn plants is an average of 8.2 percent cob, 46 percent grain, 7 percent husk, 11.6 percent leaf and 27.5 percent stalk. Corn residue consists of the stalk, leaf, husk and cob as well as any grain left behind by the combine.
On a dry matter basis, corn leaves typically consist of 76 percent, husks are 55 percent, cobs 58 percent and stalks 31 percent. In past years, crude protein in leaves has tested on average 6.2-7.5 percent. Husks tested an average of 2.6-3.8 percent, cobs at 2.1-3.8 percent and stalks at 3.0-5.1 percent.
Cobs are relatively digestible but very low in protein. Stalks are low in both protein and digestibility. Cattle, selective grazers by nature, choose the most palatable and nutritious plant parts first.
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More recent testing is showing crude protein at 5 percent, TDN 49, and ADF (acid detergent fiber) 42.4. The greatest nutrition in corn stover is found in leaves and husks. The longer cows graze a field, overall nutrition continues to decline because the percentage of husks and leaves declines. Rain, snow and excessive trampling also detract from overall nutrition because it reduces the volume of available leaves and husks.
"Many variables affect nutritional levels of corn stalks, including soil types, moisture content, etcetera," Fisher says. "That's true within each field as well as from field to field."
Corn farmers and/or beef producers can obtain a residue analysis from a lab by submitting 20 to 30 small residue samples taken from a field. Fisher recommends gathering samples from across the field so the resulting analysis is as comprehensive as possible.
"A good representation of samples will about fill a gallon bag," Fisher says. "Don't close that bag up till you're ready to mail it. And be sure to send it early in the week so the bag doesn't sit somewhere two or three days before it arrives at its destination. If it sits too long it will ferment and the samples spoil. Most labs will turn analysis of samples around in a week to 10 days."
An additional reason beef producers may want to validate nutritional levels of corn residue is recent bovine research showing that cow nutrition during gestation impacts calf health and performance throughout their life.
"Beef producers used to believe cows in mid-gestation could lose some body weight without any adverse consequences," Fisher says. "New research is verifying there is no period during which it's safe or economically feasible to allow gestating cows to lose weight."
In addition to analyzing protein levels of residue, beef producers should ensure that cattle are obtaining adequate energy from corn stalks and stover.
"Corn grain provides TDN energy levels of about 90. In comparison, corn stover would typically be 40 or 50,"Fisher says. That gives beef producers an idea of what kind of energy supplement they need to provide to cattle on corn stalks."
Cover crops can add nutrition to crop residue if moisture levels and seasonal temperatures permit.
"Many farmers interseed foxtail millet in wheat stubble and brassicas with corn and soybean residue," Fisher says. "Cover crops can provide a high-quality supplement to crop residue."
Fisher also cautioned that beef producers reconsider the length of time they graze crop residue.
"When I was growing up, it was common to graze residue for 60 days," Fisher says. "With today's combines, there's not as much corn left behind. If cows are left on today's corn stover more than 30 days, they probably need a significant protein and energy supplement."
In calculating the economic benefit of grazing stalks, beef producers should consider the cost of fencing and water, possible compaction issues and the possibility of early snow or exceptionally cold temperatures.
"With the trend toward farming larger fields, many fence rows have been taken out and wet fall weather could bring some compaction issues," Fisher says. "Still, grazing corn stalks is a good value. We sometimes forget what our grandparents did and why. With current land prices and input costs, grazing stalks can still be cost effective."