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Herbage Mass - Assessing pastures in NSW

What is herbage mass?

  In NSW, herbage mass is used to describe the quantity of pasture available to a grazing animal. Herbage mass refers to the total amount of pasture present and includes both green and dead material. It is measured in kilograms of dry matter per hectare (kg DM/ha) and can be visually assessed by considering three key factors:

·         pasture height
·         pasture density
·         water content (i.e. dry matter).

What is the difference between herbage mass (HM) and feed on offer (FOO)?

FOO is used in some other Australian states to estimate pasture availability. The primary difference between HM and FOO is the harvesting method used to cut the pasture and calibrate visual estimates. To measure HM mass, pastures are harvested using a shearing handpiece held as close to the soil surface as possible, while the standard procedure for FOO measurement uses a scalpel to harvest available plant material at ground level. Not surprisingly, the physical differences between the shearing handpiece and scalpel result in different amounts of herbage being harvested - the handpiece will typically leave about 4 mm of plant material at ground level.

The amount of residual pasture left by the shearing handpiece and hence the difference between HM and FOO measurement of available pasture will differ primarily depending on the density of the pasture being measured. The denser the pasture, the greater the amount of residual material left in situ by the shearing handpiece.

A comparison of the difference between HM and FOO by CSIRO and the Victorian DPI in the early1990s found that the difference between the two measures varied between 2 and 600 kg DM/ha dependent on pasture density. This work identified 300 kg DM/ha as a reasonable average difference between FOO and HM. Therefore the following equation should be used to covert FOO to HM:

                HM = FOO - 300 .

What are the HM benchmarks for sheep production?

The critical range of herbage mass for sheep production varies between 400-1700 kg DM/ha. The minimum HM requirement to maintain satisfactory production levels for sheep will vary depending on the class of sheep (i.e. growing, dry, pregnant or lactating) and the digestibility of the pasture. Target HM benchmarks for sheep in NSW are described in terms of minimum HM to maintain satisfactory production levels (Table 1)

Table 1 : Minimum herbage mass (kg green DM/ha) to maintain satisfactory production levels. (Source Prograze®)

 

Pasture digestibility

Sheep class

75%

68%

60%

Dry

400

600

1200

Pregnant

 

 

 

   - mid

500

700

1700

   - late

700

1200

ns

Lactating

 

 

 

   - single

1000

1700

ns

   - twins

1500

ns

ns

ns = not suitable. At these digestibilities, regardless of HM sheep are unlikely to maintain their weight and some type of supplementation is required.  

As pasture density declines pasture height becomes the critical factor (eg lucerne paddocks)

NSWDPI pasture assessment resources

Assessment of pastures is a vital skill to allow sheep producers match pasture availability with animal production and make timely management decisions regarding feed budgeting and manipulation of pasture production and composition. It is equally important that sheep producers become familiar with attributes of pasture which most critically affect animal production and to be able to accurately interpret objective descriptions of pastures in relation to animal performance. Prograze® courses, run by NSWDPI Livestock Officers, provide skills for participants to assess pasture characteristics influencing pasture and animal production and to develop pasture and livestock management plans. In addition NSW DPI has produced a series of Primefacts related to sheep production from pastures and supplementary feeding:

Pasture assessment and livestock production (Primefact 323)
http://www.dpi.nsw.gov.au/aboutus/resources/factsheets/primefacts/pasture-assessment-livestock-production

Measuring herbage mass - the median quadrat technique (Primefact 324) http://www.dpi.nsw.gov.au/aboutus/resources/factsheets/primefacts/herbage-mass-median-quadrat-technique

Supplementary feeding of sheep in southern NSW (Primefact 331) http://www.dpi.nsw.gov.au/aboutus/resources/factsheets/primefacts/supplementary-feed-sheep-sthn-nsw

Full hand feeding of sheep - management (Primefact 345) http://www.dpi.nsw.gov.au/aboutus/resources/factsheets/primefacts/full-handfeeding-sheep-management

Full hand feeding of sheep - feeding management (Primefact 346) http://www.dpi.nsw.gov.au/aboutus/resources/factsheets/primefacts/full-handfeeding-sheep-feeding-management

Full handfeeding of sheep - quantities (Primefact 347) http://www.dpi.nsw.gov.au/aboutus/resources/factsheets/primefacts/full-handfeeding-sheep-quantities

How pasture characteristics influence sheep production (Primefact 530) http://www.dpi.nsw.gov.au/agriculture/livestock/sheep/sheep/pasture-sheep

Supplementation guide for sheep: Central and southern NSW (Primefact 532) http://www.dpi.nsw.gov.au/aboutus/resources/factsheets/primefacts/supplementation-guide-sheep

For more information on pasture assessment and sheep production or Prograze® courses , contact your local NSW DPI Livestock officer (Sheep & Wool).

   
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Last Updated
March 17, 2011