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Determining available forage

By Gary Sliworksy
Following is the first of a two part article on determining the amount of forage you have available on pasture for your livestock.
Pasture is a feeding system. Like any feeding system it is important to know the needs of your livestock and the amount of feed you are offering. Think of your pasture field as a feed bunk.
When feeding in a bunk or manger you offer your livestock the quantity of feed they need to get to the next feeding while maintaining feed quality at the highest possible level. Estimating the pounds of feed on a pasture may seem like a tall task, but it is important if you are going to achieve the potential of the pasture and livestock.
There are two steps to this process:
determine the nutritional needs of your livestock, and
determine how much forage is available for grazing each day.
Step 1 - Determine Livestock Requirements
The nutritional needs of livestock are generally calculated in terms of dry matter (DM). Dry matter intake of 3% of body weight is frequently used for growing and producing livestock. A 1,200 lb cow requires 36 lbs of DM per day (1,200 × 0.03), and a 1,500 lb cow requires 45 lbs of DM per day (1,500 × 0.03). This may be slightly more than their actual needs, but it allows for some feed refusal. If we take the total weight of the herd multiplied by 3% we get the feed required per day on pasture.
Step 2 - Determine Pasture Available
The second step is to determine how much grass or forage is available on a given area for the livestock to graze. This can be done by one of 3 methods:
Grazing Stick - A grazing stick enables you to measure the height and density of the grass by how visible the stick is on the ground. Using a table of height and density printed on the stick, you can estimate the forage DM available.
Rising Plate Meter - An 18 inch square plexiglass plate 1/8th inch thick is used to slightly compress the grass to a constant density. The height of the compressed grass is measured and a chart is used to estimate the DM available per acre.
When calculating the amount of forage in the field, remember that you want to leave 3-4 inches of residue to re-grow and start the development of the grass for the next grazing cycle. Subtract this 3 or 4 inch height from the total height to get the usable height.
Next week is another way to measure the amount of pasture and a method for calculating the head / acre /day