[by Jason Hastie]
Good grazing management will play out as a profitable balance between animal and pasture production. No matter the grazing system, its sustainability is based on the manipulation of stock numbers and stocking density in the context of feed availability and plant recovery. Lots of different grazing systems have been developed but they are all variants of the following systems:
Continuous grazing (set stocking or open range grazing) – Under continuous grazing, all paddocks are grazed without spelling for long periods of time.
Deferred grazing – Under deferred grazing, paddocks are regularly spelled (rested). The spelling of paddocks is usually done for management reasons such as to encourage the regeneration of perennial plants. At any one time, more of the property will be subject to grazing than spelling.
Rotational grazing – Under rotational grazing systems, herds systematically graze one paddock at a time at relatively high stocking densities. Stock movements are based on feed availability and a specified plant recovery period for the grazed paddock. At any one time, more of the property will be subject to spelling than grazing.
There is a trade-off in the intensification of grazing management. As stock density increases from continuous grazing to the more intense forms of rotational grazing, the requirement for more active management, labour and infrastructure (fences and watering systems) increases. Whether this is worth the effort and investment, or not, depends on the manager but it needs to be noted that several studies have shown that less intensive management can be just as profitable as the more intensive forms.
Investigating Intensive Grazing Systems in Northern Australia Project
For those interested in quantified outcomes of different management Meat & Livestock Australia (MLA) has provided some information in their report Investigating Intensive Grazing Systems in Northern Australia October 2011.
The project found that the intensity of the grazing system had no consistent effect on soil condition, pastures, carrying capacity or production when compared to less intensive systems. Rather, the report confirmed other studies that have consistently shown that stocking rate management, rather than grazing system, is the major driver of pasture and animal productivity.
The Wambiana grazing trial has be running since 1997 and has been continuously evaluating several different grazing strategies.
The project outcomes so far suggest that an optimal grazing strategy includes moderate stocking at or about long-term carrying capacity, some flexibility in stocking rates in response to seasonal conditions, wet season spelling and control or amelioration of area selective grazing. One of the advantages of the moderate stocking rate was a reduced requirement for management decisions and thus management risk.
Your pasture utilisation rate will determine the outcome of your grazing management. A high utilisation rate will kill productive perennial grasses. MLA recommends a utilisation rate of between 15 per cent and 40 per cent, dependant on where you are. Lower utilisation is recommended for dryer areas.
The utilisation rate we are interested in is calculated by weight. Most of the weight of a grass plant is near the base of the grass tussock, thus 30 percent utilisation of a grass plant by weight is different to 30 per cent by height.
The Pigeon Hole Project, undertaken in the Victoria River District of the Northern Territory, found that 20 per cent utilisation was the optimal level for land condition, pasture diversity and individual animal production in their environment.
At Pigeon Hole, utilisation above 21 per cent led to unsustainable increases in bare ground, palatable plant species declined, individual animal weight gain was reduced by 10kg, breeders took 1.5 months longer to re-conceive and weaning rate was nearly 10 per cent lower.
Dependant on the size of your grass tussocks, a utilisation rate of 20 per cent probably means leaving at least the lower 20cm of grass tussocks in place. Whatever your sustainable level of pasture utilisation is, once achieved, you will be correctly matching stocking rate with carrying capacity.
We started discussing grazing management but, as stated above, stocking rate – to achieve a sustainable utilisation rate – as opposed to grazing management per se, has been shown to be the major driver of pasture and animal productivity.
This project is supported by funding from the Western Australian Government’s State NRM Program, supported by Royalties for Regions – Capacity Grant – CCGS 15756 – Upper Gascoyne Natural Resource Management Information Exchange.