Budgeting and Measuring Pasture Production
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:
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:
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.
Sample & Weigh
A more accurate method is to harvest 2 or 3 square feet of grass, weigh the amount harvested and dry a representative sample to determine the amount of DM. (Note - 2 sq ft is 1'-5" × 1'-5".) You should sample several areas of the pasture to get a representative value. The sample can be dried in a microwave oven. Weigh a sample of approximately 100 grams and microwave for a couple of minutes. Re-weigh, microwave again for a minute and weigh again. Repeat this procedure until the weight does not change. Put a cup of water in the corner of the microwave to avoid damaging the microwave. Percent DM is determined by dividing the dry weight by the wet weight multiplied by 100.
For example, with a wet weight of 100 grams, and dry weight 20 grams, the DM will be 20% (20/100 × 100). If the weight from two square feet is 200 grams and the DM is 20%, then there is 20 grams of dry matter per square foot (200 × 0.2 ÷ 2). An acre (43,560 square feet) would have 871 kg of forage available for grazing (0.02 kg/square foot × 43,560 square feet). If we multiply this number by 2.2, the 871 kg is converted to 1,916 lbs.
Calculating Head / Acre / Day
If the grass you measured indicated that there was 1,916 lbs of DM available for grazing, then this would support 63,873 lbs of animal per acre (1,916 ÷ 0.03). For every 63,873 lbs of animal you need to offer one acre of pasture for each day that they are going to be in the pasture. Ideally this will be one day, and should not be more than 5 days because intake will drop. The best grass is eaten the first day, and by the fourth or fifth day the pasture is pretty well picked over. This is very important for stocker cattle where you are looking for good gains, because you want to have them eating the maximum amount of forage each day. Stocker cattle that are moved to fresh pasture every one or two days throughout the grazing season should gain 300 lbs in a 5 month grazing season.
Knowing how much forage and dry matter that you are offering to
your pasture animals will allow you to get maximum performance from
both the livestock and the pastures.
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