Pasture, like any asset must be managed to achieve optimum performance. However, before you can manage a pasture you will need to know just how many animals of a particular type your pasture might support.

In order for you to calculate the stocking rate for your pasture for cattle, horses, bison, or sheep and goats or other grazing livestock then you are going to have to get to grips with the concept of animal units (AUs), animal unit equivalents (AUEs) and animal unit months (AUM) An AU can be:

• One 1,000lb cow with or without an unweaned calf
• One 1,000lb horse
• One 1,000lb bison cow with or without an unweaned calf
• Five 100lb ewes or nannies with or without an unweaned lamb or kid

The basic rule of thumb is that, with slight species and gender variations, 1,000lbs is an AU, except for ewes and nannies, which are approximately five to the AU. Rams and bucks are heavier and are around 0.26AUs each. It is also important to bear in mind that today's cattle are often more towards the 1,200lb mark than 1,000lb. Therefore, larger animals that are over 1,000lbs in weight must be assigned an acceptable AU figure of more than one AU by working along the lines that 100lbs of additional weight equates to an additional 0.1AU. For example, a 1,500lb horse would be a 1.5AU.

An AU will consume approximately 780lbs to 1,000lbs of dry forage per month, this is called an AUM. If it is in pristine condition, an acre of pasture could support one AUM. However, it is more realistic to work on a premise that an acre of pasture will support 0.75AUM and perhaps less if the pasture is poor.

Grazing leases will often have a capacity expressed in a number of AUMs. To calculate how many AUEs that you should be able stock this pasture with you must first:

• Calculate the average animal weight of your herd, for example, we will use 1,200lbs for this exercise
• Add 0.1 per 100lbs to arrive at a figure for an AUE, which in this case would be 1.2AUE
• Look at the lease grazing capacity, we will use 75AUMs for this exercise
• To arrive at an adjusted stocking rate for the pasture divide the grazing capacity by the number of AUEs, which is 75AUMs divided by 1.2AUE, which equals 62.5 animals for one month's grazing only
• Assuming you can effectively use the lease for grazing for five months you then divide 62.5 by five, which equals, rounded down that the pasture should support, again rounded down, 12 animals of an AUE of 1.2

Working the other way and assuming that you have a 50 acre pasture in reasonable condition then you need to:

• Multiply the number of acres by 0.75AUM, which equals 37.5AUMs
• Divide 37.5 by your AUE figure, in this case we will use 1.2AUE, which equals, rounded down, 31 animals for one month's grazing only
• Divide 31 animals by the number of months you intend to graze the pasture, in this case five, and you will see that the pasture should support, rounded down, six animals of an AUE of 1.2

In order for these calculations to work accurately your pasture must be managed and monitored. This will be covered in a future article.