Hopefully you have started a grazing plan for your ranch by developing your goals and begun getting a ranch inventory put together. We will discuss how to balance the forage inventory with the animal inventory.
To begin with balancing your forage inventory to your animal inventory, we are going to have to convert your forage production into animal unit months (AUMs). When you did your forage inventory, you should have come up with an average figure for pounds per acre for each pasture. We then determine harvest efficiency, or the amount of the available forage that the livestock are going to consume during the grazing period. A good rule of thumb that most grazers go by is take half leave half for conservative grazing. This means of the forage available, 50 percent of it is going to disappear through what is taken in by the animals, trampling, insects, and decay. Remember, harvest efficiency is just the amount that is going into the animal. In a take half leave half system, most people figure that half of what disappears is consumed by the animal, or in other words, 25 percent of the total forage production is being consumed by the animal. So a harvest efficiency of 25 percent is a good starting place. Now, to determine AUMs, you take the amount of forage that is consumed by the animals and divide it by 912 pounds, which is how much one 1,000-pound cow with a 6 month-old calf will consume in 1 month. For example, let’s say pasture 1 has an average production of 2,000 pounds/acre. We take our forage production times our harvest efficiency (2,000 pounds x 25 percent = 500 pounds available for the animals to consume). Now, we divide the 500 pounds available by 912 (pounds consumed by 1 animal unit or AU), which equals .55 AUMs/acre. If Pasture 1 is 160 acres, then that pasture will produce 88 AUMs. Do this for each pasture and total them up all up. Let’s say pasture 2 is 200 acres and produces 3,000 pounds/acre. Then 3,000 x 25 percent = 750 pounds available /912 pounds = .82 AUM’s/acre x 200 acres = 164 AUMs for pasture 2. When you add pasture 1 and pasture 2 (88 + 164 = 252) you get 252 total AUMs on the ranch.
You should have your animals converted to animal units but let’s run through an example on how to do that. Let’s say this ranch run 30 head of 1,200 pounds mother cows and 1 mature bull. The animal unit equivalent for a 1,200 cow with a calf is 1.2 and for a mature bull it is 1.4. To determine your total animal units, you multiply the number of head of each by the animal unit equivalent. For the cows it is 30 x 1.2 = 36 AUs and for the bulls it 1 x 1.4 = 1.4 AUs. When you total these two you get 37.4 AUs. To determine the AUMs required, you multiply the total AUs by the number of months you plan on grazing. So if you are going to be grazing this herd for 6 months, you multiply the total AUs by the number of months (37.4 x 6 = 224.4 AUMs required).
To balance forage inventory with your animal inventory, you simply compare these two numbers. The ranch produces a total of 252 AUMs and you need 224.4 AUMs in order to feed the number of livestock. This means you have an additional 27.6 AUM surplus. This can be saved for winter grazing or for wildlife habitat or you could also increase the herd size by about three head of cows. Knowing your available forage and forage demand is essential to developing your grazing plan. For additional information please visit www.iGrow.org.
Source: Kyle Schell
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