Putting beef cows out to tramp through the snow to graze standing corn has become more popular in the last few years. It’s relatively low-cost forage which can make up a sizeable portion of a pregnant cow’s overwinter diet because whole corn plants (with ears) can provide a significant amount of dietary energy and protein.
Since nutrient supplements may be required later on as beef cows approach calving, producers might conduct a midwinter review to assure herd nutrient requirements are met until calving.
As a beef nutritionist, I find it amazing that corn plants that literarily have dried up and turned brown right before my eyes in the late fall can be very nutritious for gestating beef cows. In any given year, the nutrient value of standing corn is high in dietary energy and similar in protein when compared to other common low-cost forages.
In my experience, corn residue (second column of table below) after grain corn harvest is very comparable to barley straw, so it makes sense that standing corn with a full ear of corn would be similar in nutrient value to an unharvested barley crop with whole kernels still in the head. I have recommended both to support the nutrient requirements of mid-gestation cows and to support an early-term fetus — 52-55 per cent TDN and eight to nine per cent crude protein fed on a daily basis for body maintenance.
In comparison, late-gestation cows (two to three months prior to calving) require a higher plane of energy and protein nutrition; 55-60 per cent TDN and 11-12 per cent crude protein, but now are responsible to support a late-term fetus and maintain an optimum body condition score of 2.75 (1 = emaciated, 5 = obese) by calving. While it is widely accepted that corn grazing will take care of these energy needs, the corn is still short on dietary protein, given that it contains only about seven to eight per cent protein.
There are many protein supplements available that help complement a beef-feeding program based on grazing corn. High-protein (28 per cent) distillers’ grains are widely available and can be used in total mixed rations (TMR). Many producers rely on commercial 18-30 per cent protein range cubes/pellets made from the same distillers’ grains and other byproducts such as wheat-mids or canola meal. If low-moisture molasses protein lick-tubs are used, I recommend producers supply one 30 per cent protein molasses cattle lick-tub for every 25 beef cows to enhance the modest protein diet of grazed corn.
I often visit a beef producer who uses about a dozen of these cattle lick-tubs as a supplement for 300 white-faced red and black cows grazing 150 acres of cornfields. He has the corn divided into five 30-acre paddocks for 100 days of winter grazing. He also limits his cow herd’s grazing activity by moving an electric fence throughout each paddock. He allows his 300 cows to graze about six to seven acres at a time for about seven to 10 days before he moves the fence onto new ground.
In this way, he prevents acidosis upsets, since palatable ears are eaten first (two to three days), then the leaves and stalks (next two to three days) and finally leftover stalks (final three days). At all times, a total mixed ration of corn silage, alfalfa hay and minerals are available outside the fenced-off cornfields and placed within access to automatic waterers.
My friend says that grazing corn is not an exact science. First, it has been his experience that after a few months, the feed quality of cornfields tends to degenerate. And second, as January/February weather becomes colder, the beef cows’ dietary energy requirement just to stay warm increases by two per cent for every 1 C drop in temperature below 0 C. To remedy both concerns, he often drops fair/good quality hay bales among the corn rows.
His story is a testament of reviewing his grazing corn program for overwintering his beef cows, namely:
1. Having a good estimate of the carrying capacity of cornfields at all times,
2. Supplementing the cornfield nutrition with extra dietary nutrients, and
3. Reviewing cow body condition. By embracing these points the program yields healthy newborn calves at calving time.