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Why is calculating forage demand important?

Forage budgeting doesn’t just improve pasture use; it also helps to prevent overgrazing.

As well as being able to calculate the amount of feed supply to complete a forage budget, we also need to be able to estimate how much our livestock eat (their intake) to estimate feed demand.

To do this, we need to know the numbers and classes of animals on hand.

Being able to reconcile your herd and accurately calculate your current stock numbers is critical to matching your feed supply with feed demand.

“The measure of who we are is what we do with what we have” – Vince Lombardi

How do we assess what our feed demand is?

It’s useful to have a standard benchmark when determining intake. For cattle, feed demand is assessed by calculating the number of Animal Equivalents (AE) on hand and then using a daily intake constant per AE to determine feed demand.

What is an AE (Animal Equivalent)?

An AE is a standard unit of measure for livestock. The measurement describes and quantifies, in commonly recognised units, the grazing pressure placed on pastures by foraging ruminants.

The AE rank assigned to an animal is determined as the ratio of its metabolisable energy (ME) requirements relative to that of a ‘standard animal’.

The ‘standard animal’, which is equivalent to 1 AE, is a 450 kg Bos taurus steer at maintenance (i.e. with zero weight gain) walking 7 km/day. The ME requirements of the standard animal are 73 MJ/day where a standard diet of 55% dry matter digestibility (DMD) is assumed.

How do I convert from a DSE to AE?

For reference, a DSE (Dry Sheep Equivalent) is a 50 kg wether at maintenance (zero weight gain) walking 7 km/day. One DSE eats around 0.95 kg of DM/day.

1 AE = 8.4 DSE

How much will an animal eat?

The ME or intake requirements of animals depend on:

  • size of the animal
  • stage of growth, pregnancy and lactation
  • quality of the feed
  • stocking rate (higher stocking rates result in poorer quality feed components being consumed by livestock).

Other factors that influence intake

The amount that animals eat can varies considerably depending on:

  • time of year, stage of pasture growth or senescence
  • type of pasture
  • pasture availability
  • digestibility of pasture
  • stocking rate
  • land type. 

It is important to note that feed intake is limited by the pasture digestibility.

To learn more about nutrition and supplementation, the MLA Nutrition Edge workshop covers these topics in great detail

Increase in intake due to supplementation

The other factor that influences the intake of stock is whether a supplement is used or not.

Protein supplements (e.g. lick) stimulate the activity of the rumen microbes which break down the feed.  This improves the animal’s ability to utilise poor quality feed. Generally, the lower the quality of the feed, the greater the effect on intake.

Any supplement which provides a source of nitrogen or protein will increase intake by  ~10 to 30%.

Urea based supplements increase intake because they increase the speed that the pasture flows through the rumen. Intake increases the most when pasture is more digestible.

To learn more about nutrition and supplementation, the MLA Nutrition EDGE workshop covers these topics in great detail.