There has been a continued increase in the use of corn for forage (grazing and silage) production in Western Canada. The Census of Agriculture indicates corn used for silage production in Saskatchewan has increased from 4,353 acres in 2001 to 16,583 acres in 2006, and 26,786 acres in 2011. An increasing number of cattle producers are incorporating corn into their fall and winter grazing practices.
New forage varieties of corn have lower Corn Heat Unit (CHU) requirements, higher yields, lower fibre levels and increased levels of digestibility. The CHU indicates how many heat units are needed for the grain to reach maturity. Provincial CHU maps are available to help determine the average CHU ratings for various locations in Saskatchewan. Work done in Manitoba indicates that corn used for forage compared to grain production requires 200 less CHUs to reach 65 per cent moisture content (whole plant). This is the point where corn is usually cut for silage.
A review of several research papers indicates 60 per cent or more of the total dry matter contains the grain, cobs and husks. The balance of the dry matter comes from the leaves, stalks and tassels. When the moisture content in whole plant corn is about 65 per cent, the average Total Digestible Nutrient (TDN or energy) level is around 65 per cent. The Crude Protein content averages eight per cent to 8.5 per cent. These values are 100 per cent Dry Matter (DM) basis. There will be variability in the energy and protein levels, depending on the year and many other factors. A feed analysis is always recommended to obtain accurate values prior to feeding or grazing.
A 1,400 pound cow, six months pregnant with outside air temperature of -10 C, requires a diet containing 62 per cent TDN and eight per cent Crude Protein (100 per cent DM). In most situations, corn used for grazing meets or exceeds the energy and protein requirements for early and mid-winter conditions. Calcium levels tend to be low in whole plant corn. Use a 2:1 or 3:1 mineral containing salt to encourage ready intake.
When cut at 65 per cent moisture content, most of the cobs will have filled with grain. As cattle are turned out to graze the standing corn, many will focus their attention on consuming the cobs, ignoring the leaves and stalks. There have been reported cases of grain overload and free gas bloat.
To avoid those problems, producers have had good success using electric fencing to graze smaller areas of the field. Narrow alleys are created by pushing down corn plants with a front-end loader or a quad. A two-wire electric fence is placed in the middle of the open alley. The alleys have to be wide enough so that corn plants knocked over during grazing do not fall on the charged wires.
Ideally, the paddocks should be sized to provide three days of grazing. The bulk of the corn stalks should be eaten before moving the cows to the next paddock.
Long term trials have shown that one acre of corn would provide 250 cow days of grazing (1,400 pound cows), 150 cows grazing for 60 days require 150 X 60 = 9,000 cow grazing days ÷ 250 cow grazing days per acre equals 36 acres of corn for grazing.
For more information on this, or other forage related topics, contact Bryan Doig, Regional Forage Specialist at 306-446-7477 or the Agriculture Knowledge Centre at 1-866-457-2377.
