Corn Residue Grazing Helps Cows, Farms
Stocking Rate and Proper Grazing Length of Corn Residue Helps Cows and Crop Ground
REDFIELD, Iowa (DTN) -- With harvest in full swing, cattle producers are anxiously awaiting turning out their livestock on cornfields for residue grazing to help extend the time needed before needing to use stored winter feedstuffs.
Mary Drewnoski, a University of Nebraska beef systems specialist, said the amount of time cattle can graze on cornstalks depends on the yield in the field. She said this during a webinar hosted by the Iowa Beef Center recently. "We like to look at it as one cow can graze for one month for every 100 bushels of corn grain taken off the field," she explained. "And we target 50% use of the leaf and husk, which is about 40% of the residue, but a lot of that is unsuitable for the cow to utilize."
For example, if the field is 160 acres and makes 250 bushels per acre and the producer has 150 cows, the math is 250 bpa per 100 bushels of corn equals 2.5 cow months per acre. "If you have 160 acres times 2.5 cow months per acre that equals 400 cow months. Then divide that by 150 cows and you would have 2.7 months of grazing or 81 days of grazing on average for a 1,300-pound cow," she explained.
KNOW WHAT IS AVAILABLE
Drewnoski said the amount of corn stover doesn't necessarily always increase based on yield and if the yield is extremely high, there can be a decrease in residue, but the general rule usually will apply. Having a conservative estimate of available grazing time based on yield is a good place to start when it comes to determining stocking rates in a field.
"Forty pounds of residue is the average amount of residue that we'd expect per bushel of corn grain produced. Corn grain is 56 pounds per bushel, but there is a lot of residue per bushel that's being produced and about 40% of that, or 16 pounds, is husk and leaf," she said.
The husk is the most digestible component, but only makes up about 8% to 10% of the residue and the leaf makes up about 30%, with the cob and stem making up the other 60%. Cows will usually eat the husk and leaf first. The residue can meet a dry cow's needs without added supplementation other than vitamins and minerals.
As the cows are on the field longer, they select the best and most nutritious part of the residue first, and over time the energy content of the diet declines as does the intake because the cows are spending more time searching for the desired material.
"If we leave the cows on the field too long, or we graze too far and try to use more of the leaf and husk, we run into a problem of the cow not getting enough into her body," Drewnoski explained. "So, it's a combination of the diet quality is changing, and her intake is changing. We want to leave them on the field only as long as they are receiving what they need nutritionally."
NUTRITION QUALITY NEEDS WATCHED
Corn residue is sometimes thought of as low quality, but she said it is actually good in terms of energy content. It's low in terms of protein content, but in other situations where the forage quality is lower, it can also be lower in digestibility or energy and protein. In this case, she recommended feeding supplemental protein to ensure the calf in utero is receiving the needed nutrients. If cows are lactating and raising a calf while on cornstalk residue, they likely will have different requirements and supplementation will be needed.
RESIDUE GRAZING AND COMPACTION
"We are also conducting studies on if cattle are causing compaction issues in fields that are grazed," she said. "When we talk about compaction, I think a lot of people think about penetration resistance and how much force it takes for those plants to actually go through the soil."
Drewnoski said if a farmer has a piece of ground that is drier versus a piece of ground that's wetter, the drier ground will always have an increase in penetration resistance. Since soil moisture is a big factor in compaction, the variabilities are so vast in each field, that it is hard to compare properly.
"We see no negative effect on organic matter with grazing and no significant effects on soil," she said. "We can see some positive effects of grazing in a high-yielding no-till situation. We actually saw an increase in the soil microbial community, so the total microbes in the soil increased with grazing compared to not grazing."
Fall grazing of cornstalk residue shows very little effect on the crop ground and yields when it is at a normal stocking rate. Relative to not grazing, there might be a slight increase, but not enough to affect the crops. Drewnoski did say there may need to be more down pressure when planting on fields that weren't grazed versus those that were grazed, but as long as stocking rates and length of grazing time are monitored, it will be beneficial to the cows and to the farm ground.
"I think fall grazing really is very low risk in terms of negative impacts on the farm ground and even spring grazing is doable as long as you don't do high stocking density in the wettest part of the spring," she concluded. The benefits to the cow are worth having cornstalk available for grazing.
Jennifer Carrico can be reached at jennifer.carrico@dtn.com
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