I created this calculator for the OP community way back in 2013. The calculator is really an Xcel spreadsheet. You plug numbers into the yellow boxes and the answers you need show up in the dark green boxes. There are several different part to the calculator, depending on the questions you’re asking.
The first section (shown below) was designed to help you figure out how much forage you have during the spring/summer grazing season. The “Total Forage Available” answer it gives you assumes that you’ll be leaving at least 50% behind to prevent overgrazing. If you use this answer as you consider how much winter stockpile you have, note that once the grass is dormant, you can graze shorter because the plant is not actively growing.
The next section of the calculator helps you figure out how much forage your animals eat. The first thing you’ll notice is that it uses a measurement called “AUMs.” This stands for Animal Unit month. This is a measurement that is more often used in the west where government agencies lease rangeland. One AUM is the amount of forage required for one cow/calf pair, because that was what was most common on rangelands. All you have to do is enter the number of animals you have in each category. You’ll get answers for how much that group eats, and then estimates for daily and monthly rates for the whole herd.
I also included a tool to help you estimate your carrying capacity. First you enter your rotation length. This is the amount of time you anticipate it will take for the forage to completely recover. If you’re using this to plan your fall and winter grazing, you won’t have any regrowth until Spring, so your rotation will be the amount of time animals spend in each pasture. The calculator divides your rotation length by the total forage you have available from the first section. You can also use the chart of daily forage requirements in the section you just filled out to enter the amount of food one animal eats. Doing that will let the calculator tell you how many animals you can feed.
Winter Forage Needs
Now, how much forage do your animals need over the winter? Well, it depends. In this spreadsheet we’ve given you two options based on how different people prefer to manage their animals.
Option 1 includes feeding 50% of your livestock’s Dry Matter requirements. Some folks do this because they want to leave more behind to speed up spring green up.
You can use Option 2 if you don’t have stockpile and will only be feeding hay, or if you don’t feed hay with your stockpiled pasture. For either option you’ll need to fill in the number of days you’ll feed livestock, how many of those days will be covered by stockpile, daily forage requirements, and how many animals you anticipate overwintering.
Keep in mind that this calculator is somewhat generic because we wanted it to work for as many people as possible. All the numbers you get from it are estimates. You’ll have to use your experience and that of the extension specialists and Natural Resources Conservation or Conservation District professionals in your area if you have questions.
Think you can get help from Facebook? No! True, you can type in that message quick and easy, but you don’t know them, and those folks aren’t likely to know your situation. It’s always better to build a relationship with a real live person than to rely on a random commenter. Not only will you get a good answer, you’ll find other ways to work together too!. So, sit back from the computer, pick up the phone, and make a call. You’ll be glad you did!