Grazing grain sorghum stalks
By Robin Slattery
River Valley District Extension Agent
The drought this year has created a real need to utilize any available forage sources, with a good opportunity being grain sorghum stalks. On a nutrient basis, early grazed sorghum stalks are better than corn stalks, providing 7.5 percent crude protein and 52 percent TDN. For a non-lactating cow in early to mid-gestation, this is enough nutrients to maintain and even gain weight. For fall calving cows and growing calves, protein and energy supplementation may be needed, and all cattle should have access to salt and mineral.
Cows will consume anywhere from 25 to 50 percent of the residue material depending on how long they are kept in the field. It is recommend to move cattle to a fresh field every 45 to 50 days (30 to 45 days if lactating), to keep higher quality forage available. Cows will eat the grain and leaves first, leaving the poorer quality stalks until last. Strip grazing sorghum residue will best utilize the forage while providing the most consistent nutrition, but requires much more labor. Many studies have looked at if grazing of residues will hurt subsequent crop harvests and the agreed upon conclusion is not. Cattle will cycle nutrients through their body but return them to the soil through their waste. If minerals and/or supplements are fed, cattle may even be contributing more nutrients to the soil then if the field hadn't been grazed. Cattle can also reduce the need for shredding stalks, remove excess residue, and help prevent volunteer re-growth from coming up.
On average, sorghum stalks will provide for 1.5 to 2 animal unit months of grazing. An animal unit is equivalent to a 1,000-pound cow, estimated to need 680 pounds of dry matter per month. To use a more common cow size, let's look at a 1,250-pound (non-lactating) cow. She would be equivalent to 1.25 animal units and require around 850 pounds of dry matter forage. If an acre of sorghum stalks provides 1.5 AUMs this would be 1,020 pounds of forage (1.5 AUM x 680 pounds per AU). So a 1,250-pound cow could be supported on one acre of sorghum stalks for 37.3 days (1,020/850 multiplied by 30 days in a month).
It's difficult to assign a "going rate" for grazing sorghum stalks, but here is something to consider. Nutrient values of early grazed corn stalks are comparable to good quality prairie hay, currently trading around $135 per ton. Assuming 92 percent dry matter, this value increases to $146.74 per DM ton. If an acre of sorghum stalks provides 1,020 pounds grazed dry matter forage, this could be worth $74.84. Keep in mind there will be costs to fence the field, transport cattle, and haul water, salt, mineral, etc. so what a producer can economically pay will be much less than this. However, there is great opportunity for farmers to rent out sorghum residue and for cattle producers to reduce feed costs.
No "non-traditional" forage comes without risks, so there are a couple disclaimers to throw out there as well. If the combine is not efficient in capturing the sorghum grain heads and over 10 bushels per acre are left in the field, cows can founder from eating too much grain heads. Of more concern with the drought this year however, are nitrate levels in the residue. It is best to collect a representative sample and contact your local extension office to send it in for testing. Nitrates will be present in the residue, but laboratory testing will reveal concentration levels so you know if the nitrates will be a concern or not. The test is very cheap compared to the risk of losing a cow or aborting a calf.
For more information contact your local extension office. Information above can be found in and Kansas State University Research and Extension's S115 "Forage Facts Notebook" (http://www.ksre.ksu.edu/library/crpsl2/s115.pdf) and UNL's EC278 "Grazing Crop Residues with Beef Cattle" (http://www.ianrpubs.unl.edu/live/ec278/build/ec278.pdf).