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Cracking the code on grazing management technology


April 25, 2024
Business tools

By means of
Beef Cattle Research Council

This article was originally posted on the Beef Cattle Research Council website on April 4, 2022.

Does it feel like general management information is shrouded in acronyms and terms that at first glance boggle the mind? Do you have trouble deciphering terms like equivalents of animal units? And how do you calculate the AUMs and then apply those numbers? Rest assured, you are not alone! There’s a lot involved in figuring out the intricacies of grazing management and figuring out how to handle the many calculations.

A good starting point is to define a grazing animal in terms of how much forage it needs to meet its nutritional needs. We know that the forage needs of grazing animals vary depending on class, weight, age and stage of production. And to account for these differences, it is useful to create a baseline to quantify forage demand.

calculating the feed requirement for animal unit equivalents

An animal unit (AU) is defined as a 1,000-pound beef cow, with or without a suckling calf, with a daily dry matter requirement of 26 pounds. By standardizing grazing animals at 1,000 pounds as one animal unit (AU), we can use that as a basis for calculating the relative grazing impact of different species and classes of livestock. We can start from one AU to adapt to other species.

Use the Calculating the roughage requirement chart to find the Animal Unit Equivalent (AUE) that best defines your grazing animals.

For example, yearlings weighing 800 to 900 pounds are considered equivalent to 0.85 animal units (AUs), while a 1,400-pound cow, with calf on the side, is considered equivalent to 1.3 AUs. Essentially, the larger the animal and the greater its nutritional needs, the higher the equivalent value per animal unit.

With a clear picture of an animal unit and its equivalents in mind, the leap to quantifying forage demand with measurements such as animal unit days (AUDs) or animal unit months (AUMs) is not difficult. If one AU requires 26 kilos of dry matter per day, we can easily extrapolate this to calculate the needs of any animal for a longer period of time.

An animal unit month (AUM) is the amount of feed required to meet the metabolic needs of one animal unit for one month (30 days). Therefore, one AUM is equal to 780 pounds of dry matter feed (26 pounds/day x 30 days).

Think of an AUM as the amount of roughage you need to feed an animal to sustain it for a month. But remember, that animal only weighs 1,000 pounds. Anything more or less must be taken into account using animal unit equivalents (AUEs).

Once you become familiar with these standardized units, they become very useful tools in determining strategy and planning different grazing options. Consider the following scenarios as examples of how you can use animal unit equivalents to lay the foundation for grazing management strategies on paper before applying them in real time.

  • A herd of 150 cow-calf pairs averaging 1,400 pounds (equivalent to 1.3 animal units; see chart above), equates to 195 animal units (150 pairs x 1.3 AUE = 195 AUs)
  • A group of 150 yearlings, weighing an average of 850 pounds (equivalent to 0.85 animal units; see graph above), amounts to 128 animal units (150 yearlings x 0.85 AUE = 128 AUs)
  • If you want to graze those 150 pairs of cowherds (195 AUs) for 6 months, there must be pastures available that can yield a total of 1170 AUMs (195 AUs x 6 months = 1170 AUMs)
  • If you graze 150 yearlings (128 AUs) for 6 months, the total forage demand is 768 AUMs (128 AUs x 6 months = 768 AUMs)

By calculating and understanding the roughage requirement, we can match that demand to the available roughage supply. The BCRC Carrying Capacity Calculator helps with that. It guides users through estimating available feed to determine the number and length of time animals can graze on a specific pasture or paddock.

Please note that these values ​​are all approximations and averages; We use numbers to estimate and standardize what’s actually happening so you can make informed decisions for your business. It is important to note that many factors are involved in managing and balancing grazing demand and available forage supply. The real world always takes precedence over what calculations try to predict, but they can provide a starting point for planning and forecasting.

You have now mastered some basic principles to understand the foundations of the art and science of grazing management. It is this crucial information that will help you navigate real-world situations, such as developing targeted grazing plans, implementing rest periods or dealing with drought and recovery.

Visit these resources to take the next steps in applying this information or to expand your knowledge: