Long-Term Grazing Intensity Research in the Missouri Coteau of North Dakota - 2011 Annual Report
Stocking Rate
There are two ways we can express stocking rate, either on a land area or a forage basis. If we express it on a land area basis, we are stating how many animals are on a given amount of land for a given length of time. If we express it on a forage basis we are stating how many animals are grazing a given amount of forage over a given length of time. The drawback of the land area basis is that forage production varies from year to year and place to place, so if we get a year with half the normal forage production we will need to cut the normal stocking rate in half, either by cutting animal numbers in half, cutting the time they graze in half or doubling the amount of land area on which they graze. If we express stocking rate on a forage basis we are keeping the ratio of forage demand to forage supply constant. If we get a year with half of normal forage production, we would still have to cut animals numbers in half, cut the length of time they graze in half or double the amount of land area on which they graze, but the stocking rate would remain the same because we are keeping the ratio of animals to available forage the same.
The unit we use for animal demand is the animal unit month (AUM). An AUM is defined as the forage required for sustaining a 1,000-lb. cow and her calf for one month and assumes they require 26 lbs. of forage a day on a dry matter basis. The animal unit is based on the metabolic weight of the animal, so a 1200-lb. cow would be 1.147 animal units and a 700-lb. steer or open heifer would be 0.765 animal units. For a stocking rate of 1 AUM/acre then we are allowing the equivalent of one mature cow and calf to graze on an acre for one month and for a stocking rate of 3 AUM/acre we are holding the equivalent of three mature cows with calves on one acre for one month, but this is saying nothing about how much forage they will have to graze. For a stocking rate of 1 AUM/ton of forage we are allowing the equivalent of one mature cow and calf to graze on one ton of available forage for one month or 66.6 lbs. per day and for a stocking rate of 3 AUM/ton of forage we are holding the equivalent of three mature cows with calves on one ton of available forage for one month or 22.2 lbs. per day. Table 3 gives examples of stocking rates in AUM/ton of available forage and their equivalent in AUM/acre assuming that the area produces 2,740 lbs./acre, the average of the loamy ecological site in our study.
Table 3. Examples of stocking rates in AUM/ton of available forage and the acres of land required to provide that much forage for one month assuming an average year’s forage production on a loamy ecological site (2,740 lbs./acre in an average year). Stocking rate in AUM/acre is the inverse of the number of acres provided. |
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AUM/ton of available forage | Acres required | Stocking rate in AUM/acre |
0.36 (average stocking rate on the light treatment) | 2.03 | 0.49 |
0.69 (average stocking rate on the moderate treatment) | 1.06 | 0.95 |
0.73 | 1.00 | 1.00 |
1.00 | 0.73 | 1.37 |
1.35 (average stocking rate on the heavy treatment) | 0.54 | 1.85 |
1.91 (stocking rate with the highest average return) | 0.38 | 2.62 |
2.43 (average stocking rate on the extreme treatment) | 0.30 | 3.33 |
2.49 (stocking rate with the highest average gain) | 0.29 | 3.41 |
3.00 | 0.24 | 4.11 |
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