What is forage supply?
Meat & Livestock Australia April 15, 2024
Forage supply is the amount of pasture biomass available for grazing in a particular area (paddock/property). It includes all pasture components down to a couple of centimetres above ground level. Only a portion of this will be available for grazing (see section below).
It is measured in kilograms of Dry Matter per hectare (kg DM/Ha). The term TSDM stands for Total Standing Dry Matter.
Pasture biomass is described in terms of dry matter due to the considerable variation in water content of differing pasture species and seasonal variations. The water component of pastures has no nutritional value to livestock so is removed when calculating biomass.
How do we measure the pasture available for grazing?
In order to measure the pasture available for grazing, we must first get a handle on pasture biomass!
This can be done by understanding the different components that influence the pasture biomass available for grazing, as well as getting out into the paddock to physically measure the pasture biomass through cutting pasture from quadrats (a small defined area).
Not all pasture biomass is available for grazing. We must account for:
- Residual = how much do we need to leave behind after grazing to ensure we are not degrading the land and compromising ground cover?
- Unpalatable (%) = what proportion of the TSDM is unpalatable species (e.g. burr, weeds)?
- Unpalatable 3Ps component (%) = 3P grasses are those that are productive, palatable, perennial. Sometimes there will be a portion of the 3P pasture species that has become rank and unpalatable to stock. These need to be accounted for as ‘unpalatable 3Ps’.
- Detachment/Wastage = what proportion of the TSDM is wasted/trampled? This is usually set at 15% but in intensively grazed systems it can be higher.
Your final number for forage supply should include the palatable feed only!
Accurately determining pasture biomass in kg DM/Ha is a fundamental skill for any grazing manager. The most common way to measure forage supply is through the quadrat method (pasture cuts and estimations). There are other methods available such as satellite technology (this will be discussed in Other tools, technologies & resources).