“The longer you wait, the poorer-quality it is. They’ll be in mid-gestation right after harvest and moving into late gestation, depending on what time they calve in March,” says Adele Harty, South Dakota State University Extension cow-calf field specialist at the Rapid City Regional Center.
“Mid-gestation is the lowest nutrient requirement, so that’s going to be the best time for them to be grazing crop residue because they’ll require the least amount of additional supplement.”
Harty says because cornstalks are a low-quality feed, a protein supplement is needed right away to keep the rumen functioning correctly. With corn stover valued at 5 percent protein, cows are going to need 3.5 pounds of a 20 percent protein supplement for proper rumen function.
“Because it is a low-quality feed, they will have to provide supplements. The cows aren’t actually going to eat many of the stalks themselves. They are going to be eating the husks and leaves and the little bit of corn on the ground,” Harty says.
As the cows stay out on cornstalks longer in the season, they will move into late gestation. Their nutrient requirements will go up, and producers will have to increase the amount of protein to meet the cow’s requirements for that growing fetus.
In addition to protein, producers will probably need to supplement for minerals. Most likely, that will mean supplementing phosphorus. That mineral tends to be fairly low in cornstalks.
Deciding how to deliver a protein supplement will depend on what the producer’s setup is and what they are willing to pay.
“It’s important when they’re looking at protein supplements to evaluate them on a cost-per-ton-of-nutrient basis,” she says.
For instance, a ton of protein from alfalfa will be a lot cheaper than a ton of protein from a lick barrel. However, producers also need to take into account the cost of delivery.
Distillers grains could be an option. Directly feeding them on the ground is OK depending on the type of ground it is being put on, but could create some waste.
Besides hay, lick barrels and distillers grains, producers could also use range cubes.
“Range cubes are a good option because they’re self-contained. You can put them right on the ground,” Harty says.
Numerous research data says producers can provide protein supplements as infrequently as once a week. Knowing that could help producers make their decision on what type of supplement to feed. For example, if a cow needs 3 pounds of supplement a day, producers could put out 21 pounds once a week.
“Those animals recycle the nitrogen through the rumen and the saliva. That’s what the microbes use. You could go out every third day and roll a bale of alfalfa out for them, and they’ll consume it and still utilize the protein for the entire period of time that they need it up to a week,” Harty says.
Once the snow has fallen, producers need to take into consideration how much leaves and husks were on the ground before it snowed and how much snow fell. If a little bit of snow has fallen, and there is still some corn residue out there, the cows can stay out there and graze.
“The biggest factor is how much is there to eat. That’s something producers are going to have to monitor. Once they start seeing mostly stalks, they need to be moving them – because they’re not going to have enough to eat, and you do not want to force them to eat the stalks themselves,” Harty says.
If a lot of snow has fallen, producers will need to either provide alternative feed in the field or move cattle to a different area where producers can more easily provide them alternate forage.
Harty reminds producers who are grazing cornstalks today to keep in mind that they are not the same cornstalks they grazed 10 to 15 years ago. With the advancements in plant breeding, there are a lot less corn and ears on the ground after harvest.
“The quality of the cornstalks, meaning the energy value, is a lot lower than it used to be because they don’t have the corn to consume that they did years ago,” Harty says.
“Be aware. Cow body condition score is going to be an indicator of how they’re doing and whether their requirements are being met. If they start slipping in body condition, something needs to change.” 
Wendy Sweeter is a freelance writer based in South Dakota.
PHOTO: Observe corn fields closely to make sure there is adequate aftermath when grazing cornstalks. If you’re seeing only stalks, it’s time to move the cattle. Photo courtesy of Wendy Sweeter.
