Cattle per Acre Calculator

If you want to know how many cows per acre can graze, this cattle per acre calculator will help you find the answer! Keep on reading to learn about Animal Unit and Animal Unit Month measures and see how the different pasture conditions influence how many cattle per acre may fit.

Do you want to ask the question another way around — How much space does a cow need? If so, you are at the right place to get the answer!

The Animal Unit (AU) is a universal measure that helps you estimate how many cattle per acre you can graze. One AU is a 1000 lb cow with a calf of up to six months old.

Typically, a cow eats forage at a rate of around 75%-80% of its mass per month. Although a calf doesn't need grass for grazing, it still consumes cow's milk, resulting in higher forage consumption by the mother.

Another standard measure is Animal Unit Month (AUM), which is the monthly forage demand for 1 AU. According to Natural Resources Conservation Service, NRCS. 1 AUM equals 915 lb.

We need to estimate the pasture forage yield to know how many acres a cow needs. The numbers may lie in a vast range from 0.25 up to 7.5 AUM/ac. Many factors influence these values:

• Pasture condition;
• Precipitation zone;
• Forage type; and
• Grazing strategy (e.g., rotational grazing).

In our cattle per acre calculator, we focus mainly on the first two factors. Check the table (from Alberta Forage Manual) to see the estimated values of forage production:

A typical 1000 lb cow with a calf (1 Animal Unit) needs around 0.27 ac (0.11 ha) of pasture in excellent condition and applied irrigation, up to 8 ac (3.2 ha) of pasture in poor condition and low precipitation level. Similarly, a 1300 lb cow with a calf (1.3 AU) requires between 0.34 and 10.3 ac or 0.14 and 4.2 ha land.

Let's go together through the step list to understand how our cattle per acre calculator works:

1. Choose a cattle type you want to graze. If you know the average animal unit of the herd, you can select the Custom option and input your own value.

2. Enter the total area of the pasture. Check our acreage calculator if you know only the field's dimensions.

3. If you don't know the forage yield, choose the annual precipitation and pasture condition. If you do know the number, you can enter the value yourself.

4. That's all! You can see pasture's cumulative forage production, the total number of cattle, and how many cows per acre can graze on the field in the result section.

5. You can also play with other parameters (e.g., the utilization rate) according to your needs. You can edit the forage yield if you know the forage yield and like to modify the lb-to-AUM conversion ratio — by default, it's 915 lb/AUM.

Now that you know how much land a cow needs and how to use this cattle per acre calculator, let's proceed to an example.

Suppose we want to know the total number of cows that can fit an 800 ac pasture in good condition. We want to keep a herd with an average weight of 1300 lb for the cows with calves. The field's location is relatively wet, which assures the average annual precipitation of 550 to 650 mm. The utilization rate is 50%.

1. Good pasture condition and precipitation zone provide the average forage yield of 2.2 AUM/ac or 2000 lb/ac.

2. The total monthly production of the field is 2000 lb/ac × 50% = 1000 lb/ac.

3. Out of 800 ac pasture, you can collect: 1000 lb/ac × 800 ac = 800,000 lb of forage. We can also write it as: 800,000 lb / 915 lb/AUM = 874 AUM.

4. An animal equivalent of our cows is 1.3, so the total number of cattle is 874 / 1.3 = 673.

5. Additionally, we can estimate how many cattle per acre it is (we assume a pair of cow and calf as a single unit): 673 / 800 = 0.84 cattle/ac.

6. We can also ask the question the other way around — how many acres do you need per cow? Simply find the multiplicative inverse of the previous number: 1 / 0.84 = 1.19 ac per cow.

If you want to learn more about different pasture condition classes, check the definitions by Alberta Forage Manual:

Keep in mind that the values in the table and the results from our cattle per acre calculator are only rough estimations, as the actual yield of a pasture varies for different legumes and grass types. Also, forage production changes throughout the year.