Quick answer: A Grazing Unit Month (GUM) is the amount of forage that provides 10 megacalories of net energy a day for one-twelfth of a year, about 304 Mcal in total. One GUM is roughly equal to one Animal Unit Month (AUM), but a GUM is measured in net energy rather than dry matter, so it adjusts for each animal's weight, class, species and stage of production instead of assuming every cow weighs 1,000 pounds.
An animal unit month (AUM) is the classic unit of measurement used to measure the forage needs of livestock as well as the forage availability of a given grazing environment.
In developing the Ranch Vision software, however, I decided to create a new, more precise unit to measure these aspects of a ranch business. It is called a grazing unit month (GUM).
In this article, I'm going to explain what a grazing unit month is and how it differs from an animal unit month.
Both AUMs and GUMs are ways to measure the forage needs of livestock as well as the forage availability of a given grazing environment.
A single AUM is roughly equivalent to a single GUM.
However, AUMs and GUMs are defined quite differently.
An AUM is defined as the amount of forage dry matter required to maintain a 1,000 pound cow and her unweaned calf for one month.
A GUM, on the other hand, is defined as the amount of forage required to provide 10 megacalories of net energy for one-twelfth of the year.
While AUMs are a somewhat crude system that has been in use for nearly a century as a measure of grazing for both federal and private lands, GUMs have been developed only recently by Ranch Vision as a superior means of measuring both livestock needs and the forage availability of grazing lands. This more precise definition provides many advantages.
GUM is a more precise unit of measurement that accounts for the realities of ranching.
The AUM was developed at a time when average cow weights were much closer to 1,000 pounds than they are today. The AUM system does not take into account how differences in cow weights would impact forage needs.
In addition, the AUM system does not differentiate between the dramatically different weights of the various animals in your herd. For example, unweaned calves. Why should one expect a 500-pound unweaned calf to have the same forage requirements as a 100 or 200-pound unweaned calf?
How do we account for bulls of varying weights? Growing steers? Heifers?
There are many other factors that impact forage demands for cattle, such as frame size, milking ability, and stage of pregnancy. The GUM measurement accounts for all of these variables.
The GUM is also more precise with the actual month unit. Why should a 28-day month be equated with a 31-day month? When planning out your ranch's finances, all of these nuances matter.
Ranch Vision is a program for cattle, sheep, and/or goat grazing operations. AUM uses a standardized cattle weight to measure forage needs. GUM accounts for alternative grazing species such as sheep and goats in their various sizes and production classes. This allows you to make accurate comparisons in light of all the factors that impact the forage requirements of different livestock herds.
The maintenance and production requirements of grazing animals are satisfied by consuming sufficient nutrients, primarily energy, not dry matter.
Net energy, which GUM measures rather than dry matter, is a much better way of assessing both livestock needs as well as the benefit provided by grazing lands.
The GUM system takes into consideration all the factors impacting net energy requirements within and between the various grazing livestock species on your ranch to create an accurate measure of both the needs of grazing livestock and the forage availability of grazing environments.
Ranch Vision uses GUM so that you can have confidence in your projections and manage toward greater ranch profit.
Designing Ranch Vision, our goal was to create a forecasting program ranchers can have complete confidence in, and that means making our projections as accurate as possible. That's why simply utilizing the AUM wasn't good enough. We developed the GUM to give ranchers better numbers and reports so that you can forecast your profits and find ways to manage your unique ranch situation to better success.
You can't make the most of your grass resources without understanding what they are and what your herd's forage demands are! Ranch Vision helps you see the future, and plan for profit.
One GUM is 10 megacalories of net energy a day for one-twelfth of a year (30.4375 days), or about 304 Mcal of net energy.
For a rough comparison, yes: one AUM is approximately one GUM. The difference shows up in the detail. GUMs scale with each animal's actual energy needs, so a herd of heavy cows or a mix of species will use more or fewer GUMs than a flat AUM count suggests.
Yes. Because a GUM is based on net energy, it measures forage demand for ewes, does, lambs, kids and cattle on the same scale, so you can compare enterprises fairly.
Grass is the raw material of a grazing ranch. Measuring it precisely lets you calculate what each enterprise earns per unit of grass consumed, which is how Ranch Vision's Enterprise Efficiency reports show where your grass makes the most money.
See your herd's grazing demand in GUMs and what each enterprise earns from your grass. Start a free 14-day trial (no credit card required), or join Dr. Brazil for a live walkthrough.