A large component of the productivity of extensive grazing systems is determined by plant herbage production (both quantity grown and time of production) and the feeding value of this herbage.
Feeding value is defined as ‘the animal production response to grazing a forage under unrestricted conditions’ and is a function of voluntary feed intake and nutritive value. Grazing ruminants require a high feed intake because:
- the gross energy of herbage is generally low
- 15-60% of ingested energy is lost via faeces
- up to 18% of the energy released through ruminal fermentation is lost through heat and gas production
- the process of grazing and ruminating can incur a high energy cost.
To achieve maximum profitability from extensive grazing systems, livestock production (value of meat, wool or milk) must be considered in relation to efficiency of production per unit of feed versus a number of costs. Direct costs include livestock health and processing, pasture establishment and maintenance and feed conservation costs.
Indirect costs are environmental outcomes and opportunity costs. This section discusses the factors influencing the productivity of ruminants from extensive grazing systems including the time of feed availability, quantity of herbage production, voluntary feed intake and nutritive value of herbage.
It concludes with a discussion about some of the opportunities perennial pastures offer to livestock production systems.
Factors influencing the value and productivity of pastures:
Time of feed availability
The cost of carrying stock through periods of feed shortage is a major limitation to the profitability of mixed farming systems in southern Australia. In Mediterranean-type environments this scarcity occurs during the late summer/autumn/early winter period.
Figure 1 shows the herbage available from a subterranean clover-based annual pasture set-stocked at 10 DSE/ha from September until March. At the start of September only 1 t DM/ha of herbage had been produced.
Two months later the pasture contained over 5 t DM/ha despite continuous grazing by 10 sheep/ha. By March only 1 t/ha of dry, low quality pasture remained.
As a result of this autumn/ winter feed gap, producers must conserve excess spring herbage, reduce stock numbers, feed costly supplements or fail to fully use the spring biomass production.
Pasture available in autumn or early winter therefore has a higher marginal value than herbage produced in the spring, i.e. a small change in pasture availability in autumn has a higher impact on whole farm economics.
Economic modelling indicates that an additional kilogram of pasture produced in the wheat belt in May has 10 times the value of a kilogram of equivalent quality feed in October.
Therefore, perennial pasture species that provide a relatively small quantity of biomass when the marginal value of pasture is high could be more profitable than annual species that provide a larger number of total grazing days but with most of the production in spring when there is a surplus of feed.
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