– Victor Shelton, Retired NRCS Agronomist/Grazing Specialist
Cows grazing corn stalks after harvest. Best the first 30 days
As I write this the last week of September, it is certainly drier than normal. This provides good conditions for grain harvesting, but slows growth on forages. I, personally, have not had any rain, only teasings for over a month. Stockpiled forage growth has really slowed down and regrowth on rotated pastures has come to a sudden halt.
I’m still banking on some rain in the near future and hopefully in time to provide sufficient moisture for fall growth. At this time, I would not recommend grazing everything down to the nubbins – nor would I ever. Maintaining enough leaf material and cover to slow further evaporation and collect dew while maintaining the solar panel, usually at least four inches of growth for most cool season forages, will help spur more regrowth once moisture is replenished. Without that reserve, plants will have to rely on root reserves for new growth and that will take more time and possibly slow future production.
What pastures really need under these conditions is rest. If we don’t get the rain needed, what forage is there is not going anywhere and it could possibly be grazed later this fall, ideally after going dormant with less detriment for future growth. It is under these circumstances that we need to strongly consider what else could be grazed to allow that needed rest for pastures.
If you have late-summer planted annuals such as oats and brassicas (such as turnips), then those could be grazed if there is enough growth on them. That growth is going to be dependent on when they were planted and the amount of moisture present. If I was low on pasture, I wouldn’t hesitate to start grazing them at even 10 to 12 inches, perhaps even shorter.
If you have any summer annuals that could be grazed, then I would graze those first, especially anything that could potentially have prussic acid poisoning issues after frosts. Those potential problem plants could include sudangrass, shorgum-sudan and even Johnsongrass. Those are best grazed prior to any frosts and may even be an issue in frost pockets. Those wilted plants, whether from stress or frost/freeze, should always be avoided by grazing livestock. However, once killed by freezing conditions, they are generally safe to graze again about two weeks later after drying down. Millets and certain genetically bred varities don’t have the prussic acid poisoning issue.
Most of the summer warm season annuals stockpile fairly well for late grazing especially when grown with a grazing turnip. The two complement each other and keep the rumen better balanced than individually.
We are well into fall harvest, specifically corn. Grazing stalks can be a valuable tool for producers trying to stretch out fall pasture and/or reduce early hay feeding. One of the first advantages achieved with grazing corn stalks in fields is nutrient retention. Most nutrients consumed are readily returned to the field and usually in a more available form than before. If stalks are “strip” grazed (allocated out in days or weekly intervals) nutrient distribution is very good and fodder quantity and quality being grazed will be a little more stable from day to day. If there is a lot of corn (grain) on the ground, then strip grazing is really important to greatly lower the risk of foundering. I don’t see this as too much a problem this year unless you have a lot of down corn or where spillage from loading areas occurs.
The nutritional value of corn stalks can vary from year to year. If you were to watch the cows graze it, you would find that they would graze or select what they are consuming in this order – any grain, then leaf, husk, and cob (somewhat dependent on variety) and lastly the stalk or stem. “Stalks” will start out in the 8% crude protein range with approximately 70% total digestible nutrients (TDN) and over a period of about 60 days will drop to 5% crude protein and 40% TDN. Spring calving cows will meet most of their energy needs during mid gestation. Growing animals such as calves and fall calving lactating cows may be lacking a little in energy and protein and most likely will need to be supplemented if they are run on stalks.
About one acre of typical corn residue will be needed per animal unit per grazing month. Weekly allocations seem to work very well so you need to figure how many acres of stalks will be needed for one week of grazing for your herd. Take number of cows times the average weight times 0.03 (average dry matter (DM) intake) times 7 days (e.g. – 50 cows X 1,100 pounds X .03 X 7 = 11,550 pounds DM needed). Now take corn yield times 0.4 (utilization) times 56 (e.g. – 180 bu. X 0.4 X 56 = 4,032 pounds per acre DM). Now divide needed pounds for one week (11,550) by pounds available per acre (4,032) and the answer is about three acres. This is a nice conservative estimate of acres needed.
With all of that said, this all is dependent on several other variables including drinking water availability, fencing, and soil and site conditions. For a field to be “usable,” it is going to have to have water available or a portable system utilized. It is also going to have to have an adequate fence to keep the cows where they are supposed to be; neighbors and passing cars seem to appreciate that. Temporary fencing (step-in posts and poly-wire on a reel) can then be utilized for those regular allocations.
At the time I am writing this, we are still quite dry in many parts of the state. Although not ideal for new forage growth or fall crops, drier conditions are ideal for grazing corn residue. Grazing stalks during wet soil conditions can increase the chances of compaction, especially on heavier soils. In Indiana. most compaction associated with grazing corn residue is in the upper layer and is normally fractured by spring by freezing and thawing.
Fields should ideally only be grazed under drier conditions as well as planted to a cover-crop such as wheat or cereal rye to help trap valuable nutrients and prevent erosion. If the field is considered highly erodible land (HEL), then you will want to ensure that adequate residue levels are being maintained according to your conservation cropping plan. Consult your local soil and water conservation office for questions regarding compliance.
Corn residue can be quite low in most minerals, especially calcium and phosphorus. A well-balanced vitamin and mineral mix should be provided, free choice, for the scavenging cows. Remember, it’s not about maximizing a grazing event, but maximizing a grazing season! Keep on grazing!