Making More from Sheep Australian Wool Innovation Limited Meat & Livestock Australia
MODULE 12: Efficient Pastoral Production
Tool 12.11
Previous Index Next

Cutting, drying and weighing the estimated amount of feed available for livestock provides an estimate of what livestock can potentially consume at a point in time. This technique is most useful for uniform feed such as grass and legume pasture or blue bush or salt bush stands.

Plant cuts can also be used for semi-uniform grazing systems such as mixed bluebush and saltbush, where the amount of feed that animals will consume is estimated when making the vegetation cuts. However, this is an estimate of actual consumption and needs to be validated through observation of livestock body condition score and grazing impact on the shrubs.

A standard quadrat needs to be used when taking cuts from vegetation. This would ideally be 1 metre x 1 metre for ease of conversion. Taking a number of cuts will improve accuracy of the estimates. Alternatively, if you wish, you can take a smaller quadrat area. Common sizes include a quarter of a square metre, or half a square metre. Be sure to know the size of your quadrat, and remember to covert to one square metre before making further calculations.M

The ‘dry’ weight of harvested feed needs to be determined; this is achieved by air drying the ‘wet’ feed and then placing into a drying oven or microwave to obtain a dry weight.

For safety, the following process should be used for determining the dry weight:

  • Record the ‘wet’ weight of the sample after it has been cut
  • If you have a large sample, take a subsample of known weight (100g is a good amount, because it makes the sums easier later on
  • Place the sample in the microwave with a cup of water (empty the cup and replace with cold water after every sample is dried)
  • Start the microwave on the ‘High’ setting for 2 minutes. Continue to dry the plant material for 2 minute bursts and reweigh until no weight change occurs
  • Record the dry weight of the sample as grams
  • Divide the dry weight by the wet weight and convert to a percentage dry weight. This can be useful for field estimates for subsequent wet weight cuts
  • If you started with 100g subsample, then your dry weight is the % dry matter
  • Multiply the total initial sample by the % dry matter to get the mass of dry matter for the sample you took.

Convert the dry matter figure collected from a 1 metre square to kilograms of dry matter per hectare in the following way:

  • If more than one quadrat cut was taken, add up the total grams and divide by the number of quadrat cuts that were taken. This will give you average in grams per square metre
  • Convert the grams per square metre to kilograms per hectare by multiplying by 10
  • If required, kilograms per hectare can be converted to tonnes per hectare by dividing by 1,000
    For example: 200gms/square metre x 10 = 2,000kg/hectare
    2,000 kg/1,000 = 2t/hectare