Interactive Tools

Some Notes On Using This Calculator:

Stocking rate (AUM/acre) has been the most widely used value graziers have relied on for decades. It is the value that is derived from taking the forage yield of a pasture, the target utilization rate, and dividing the resulting value by the estimated forage intake from an “Animal Unit.”

• One Animal Unit is one 1,000 lb cow with or without a calf. That cow is estimated to consume 800 lb of forage in one month (AUM), or 25 lb of forage in one day (AUD).

Stocking rates have been used in continuous grazing systems or loose “rotational” grazing systems where animals were generally allowed to graze a large pasture for at least one or two months at a time. Continuous grazing systems set a [small] number of animals on a large pasture base for a whole grazing season (in Western Canada, generally from May 1 to October 1).

It has been mostly useful in minimizing overgrazing, to an extent. Unlike management-intensive grazing systems that utilize paddocks and far more frequent moves, however, it doesn’t wholly eliminate overgrazing, as animals in continuous grazing systems are still free to return to their favourite areas they’ve previously grazed.

Stocking rate calculations are still valuable in rotational grazing or management-intensive grazing systems, though, so we’d be stupid to completely eliminate them. They now serve as a general indication of our pasture capacity. In order to get that general idea, we need to know three primary details:

1. What is the forage yield in your pasture? Ideally, this is best done by taking several random quadrat samples (1-ft x 1-ft squares), weighing them, then drying them in the microwave or oven and weighing them again. Wet-weight samples, when compared to dry-weight samples, can give you an idea of moisture content. Dry-weight samples provide a forage yield when compiled and averaged, then converted to pounds per acre. The other way is to estimate using Tables 1, 2, and 4 on the Pasture Management Workbook page, then adjust the forage yield and utilization rate values to get the stocking rate you are looking for.
2. What is your ideal utilization rate? This is the estimated percent value of forage that is eaten, trampled, and manured on, as well as plant matter left behind to remain as “soil armour” to protect the soil. In tame pastures, the rate is generally around 50%, with some leeway allowed of +/- 10%. The rule of thumb is to never exceed 75% to avoid overgrazing. The higher the utilization rate, the longer the pasture needs to rest. On native grasslands or modified native pasture, the utilization rate tends to be lower, at around 25 to 30%, so that sensitive vegetation is less likely to be affected, or to ensure that they have plenty of time to recover if they are eaten.
3. What is the average weight of your animals? The standard animal unit, as mentioned above, so animal weights need to be adjusted to account for the heavier average weight of modern-day cows. Larger cows tend to eat more, so an Animal Unit Equivalent (AUE) needs to be used to adjust the number of animals a pasture can hold at a time.

The calculator can be used for individual paddocks, only if you have an idea of how long animals are going to stay. Simply change the time to 1, 3, or 5 days, and you can see the required paddock size you need or the number of animals needed. Generally, however, this calculator is best for larger areas that are going to be grazed over longer periods of time.

You will notice, however, when changing your values to larger areas (100+ acres), and for longer periods (3+ months), that the number of animals you can stock on that area will be significantly smaller compared with stocking animals in smaller areas for shorter periods of time (e.g., 17 acres for 3 days). This is because, somehow in the calculations, there is an inherent recognition of more even forage utilization and better use of the forage resource when using smaller paddocks as opposed to keeping animals out on a quarter section (160 acres) or a section (640 acres) of land for 3 to 6 months. Keep this in mind when considering the options of rotational grazing versus the “easier” means of continuous grazing!