How many head of cattle can you keep on your pasture? It is a question that we often need to solve if you have a limited amount of land or want to use your land in the best way possible. As cattle producers we want to understand how to raise the maximum number of animals on the acreage we have. Additionally, if you are looking to purchase or expand your herd, it's important to understand the minimum amount of land you need to support the grazing and growth requirements of those animals.
Finding the right balance between your herd size and available forage is a critical part of developing and managing good grazing practices, no matter if you are using rotational or continuous grazing practices.
This article, and the included cows per acre calculator at the end of the post, will walk you through how to calculate the number cows that can be supported based on your pasture size -and health- and how much land is needed for each head of cattle based on the cattle type.
Why Calculate Cows per Acre?
In order to maintain the quality of your soil you can’t run too many cows per acre. If you do you can run in overgrazing issues that will impact the health of your soil and in-turn negatively effect the health and productivity of your herd.
Overgrazing is a common mistake that new ranchers make. Overgrazing can reduce soil health, quality and lead to a reduction in the biodiversity of your pasture. A pasture in poor health is more likely to allow the expansion of invasive plants and grasses to take over, which will reduce the quality and amount of forage available. Overgrazing also causes soil degradation can can cause desertification of your land.
Rotational grazing and multi-species grazing are two types of grazing you should coniser for your farm. In addition to supporting healthy pastures, rotational grazing and multi-species grazing practices can also produce healthier animals.
Before we dive into the calculator, it's important to understand the key factors that go into determining how many grazing animals the land can support. The key factors come down to the weight of the animals grazing, measured as animal units (AU), and the health and productivity of the pasture. Let's start by understanding animal units.
Cattle Animal units
The Animal Unit (AU) is a standard measure of weight that can be used to estimate how many cattle per acre you can graze. One AU is equivalent to a 1,000 lbs (453.6 kg) of body weight.
Another important metric to understand is Stocking Rate, which is expressed as Animal Unit Month (AUM). A cow typically eats about 75-80% of their body weight in forage per month. Understanding the forage rate for cows helps us to determine the Animal Unit Month (AUM). AUM is the monthly forage demand for 1 AU or roughly 915 lbs for a cow according to Natural Resources Conservation Service, NRCS.
Estimating Pasture Forage
To accurately estimate how many acres a cow needs it's important to understand the pasture conditions, precipitation, and more specifically, the estimate of the forage yield that the pasture will produce. The amount of forage that can be produced by a pasture can vary widely and can be severely effected by:
Precipitation zone
Types of forage grown
Grazing system used (e.g., rotational grazing)
Pasture condition scoring takes into consideration many factors when evaluating the overall health and productivity of a pasture and its pasture forage yield. The NRCS and Alberta Forage Manual provide extensive details about this.
Using pasture scoring to determine the pasture condition class will help you to develop an estimate for the Animal Unit Months per acre. For example, an irrigated seeded pasture in excellent condition might provide 7+ AUM/acre while the same irrigated pasture in poor condition may only yield 2.5 AUM/acre. A poor quality field in a dry year might have as little at 0.25 AMU/acre.
How much land does a cow need?
You've probably heard that you need about 1 acre per cow or about 1.5 to 2 acres to feed a cow/calf pair for 12 months. But the story really that simple. A typical 1 AU, 1,000 lb, cow might require as much as 8 acres (3.2 ha) on poor quality pasture with low precipitation or as little as about 0.27 acres (0.11 ha) on an irrigated pasture in excellent condition. As you can see the health and quality of the pasture and forage yield makes a huge difference in how many head of cattle can be supported per acre.
Now that you have a sense of how much land a cow needs to support their grazing needs, let's walk through an example to understand how to calculate the number of cows per acre that could be supported by a certain size pasture.
Let's assume that you've estimated your pasture forage yield rate on a good quality pasture with decent precipitation and determined an average forage yield of 2.2 AUM/acres or 2000 lb/acres.
Assuming that we are allowing the pasture to rest 1/2 the time by using a rotational grazing system, we can assume a 50% utilization rate.
To determine the total monthly production of the field we multiply the AUM x the utilization rate. Or 2,000 lb/acre x 50% = 1,000 lb/acre or 915 lb/AUM.
Next, we determine the total AUM for our pasture. Let's assume a 500 acre pasture. We do this by multiplying the monthly production of the field, 1,000 lb/acre) x the size of our pasture (500 acres) to get a total of 500,000 lb of forage or 546 AUM.
Assuming we want to graze an average weight of 1,200 lb (1.2 AU) - cow with calves. We can determine the total number of animals by dividing the number AUM (546 AUM from step 4) by the average animal units (1.2 AU) and then dividing by the total acres - or (546 AUM/1.2 AU) / 500 acres = 0.91 head of cattle per acre.
Ok, there's a lot of parts to that calculation. The good news is that you can just select a few options and plug in some information in the calculator below and let it handle the math for you.
Cow per Acre Calculator
Here's the basics instruction for using the cattle per acre calculator.
Choose a cattle type you plan to graze. Tip: If you know the average animal unit (AU) of the herd, select the Custom option and enter your value.
Enter the pasture area.
Adjust the utilization rate, according to your grazing practices.
If you know the forage yield, enter it, otherwise choose the annual precipitation and pasture condition option to determine the forage yield estimate.
And, that's it! Once you've supplied that information you'll see the estimated pasture's forage production, total number of cattle, and how many cows per acre can be grazed on the field.
Additional Cattle Resources
Cattle Body Conditioning Scoring
Cow Gestation Table and Cow Gestation Calculator
Estimating your Hay Needs
Beginners Guide to Keeping Livestock Records
Other Cattle Resources
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Conclusion
We hope that this article has taken some of the confusion out of calculating the number of acres you need to graze your cattle on. Best of luck and happy ranching!
