Livestock are an integral component of Mallee farming systems. However, the integration of cropping and grazing remains a major management challenge, as paddock sizes tend to be large to benefit efficient cropping practices. Furthermore, Mallee paddocks are also characterised by extreme soil variability and these variable soil types support different levels of feed availability and have different susceptibilities to soil erosion.
As a result, farmers report that they are not able to utilise all of the feed on offer within a paddock without reducing groundcover below critical levels. In situations in which farmers are forced to extract maximum productivity, soil erosion often results on the most vulnerable soil types such as sand dunes.
Advances in technology such as portable fencing systems and virtual fencing potentially offer a solution to the issue of grazing large Mallee paddocks with high soil variability. However, to effectively design and deploy these innovative grazing techniques, the grazing behaviour of livestock in these paddocks needs to be understood and quantified.
This project has begun to address this knowledge gap by quantifying livestock (sheep) grazing habits in a large Mallee paddock with variable soil types.
TAKE Â HOME MESSAGES
- In 2015, for the first time in the Mallee, sheep grazing behaviour was monitored and mapped
using GPS tracking collars. - Sheep grazing stubble utilised the paddock evenly as they sought out spilt grain during the
summer fallow, but they preferred to graze sandy soil types first. - While grazing a vetch pasture in the same paddock, livestock spent 50 per cent of the time
grazing only 25 per cent of the paddock and remaining 25 per cent was not utilised.
AIM
To quantify livestock (sheep) paddock utilisation during summer and winter grazing in a large Mallee paddock; to identify factors that may influence livestock grazing behaviour such as feed quantity, feed quality and landscape topography; and to understand the impact of stocking pressure on spatial ground cover levels within the paddock.
METHOD
A flock of two-year-old merino ewes (approximately 200) was monitored over a summer and winter grazing period during 2015 using Global Positioning System (GPS) tracking collars.
Prior to the commencement of grazing, 25 animals within the flock were fitted with UNE Tracker II GPS collars. Livestock monitoring data was supported with on-ground monitoring of vegetative soil cover and feed quantity and quality over both grazing periods.
The project was undertaken in a 107ha paddock near Nandaly which had a range of soils (deep sands to clay loams) commonly associated with Mallee paddocks (Figure 1). The summer grazing period commenced on 14 January 2015 and concluded on 24 February. The paddock was sown to barley in 2014, providing livestock with barley stubble and grain from lodged heads and grain spilt during harvest. No green plants (volunteer barley or summer weeds) were present when the livestock were introduced into the paddock.
The paddock was sown to a vetch pasture in autumn and the flock was re-introduced into the paddock on 28 July. The sheep grazed the paddock until 17 September.
At the conclusion of each grazing period, the collars were removed and the data downloaded from the GPS devices. Data was then analysed for the purpose of quantifying variable grazing pressure. Speed thresholds from behavioural modelling techniques were developed to identify when the sheep were grazing, travelling or camping.
RESULTS AND INTERPRETATION
SUMMER GRAZING
The time spent grazing a stubble paddock during 10 day intervals is shown in Figure 2. Spatial variability in grazing intensity was to be seen between the 10 day intervals, with sheep spending most time in paddock zones with lighter soil types before moving on to other areas of the paddock. This may suggest preferences for certain zone or soil types before feed became limiting and utilisation of other areas became necessary. By the end of the summer period, paddock utilisation was relatively even.
There was a very slight decline in groundcover over the summer grazing period, but, on average, groundcover levels remained well above critical levels of 50 per cent. There were already some parts of the paddock at 50 per cent when the sheep were introduced and in an ideal system, grazing would have been avoided in these zones to reduce the risk of erosion.
During summer, grazing speeds and distance travelled were very high as the sheep were constantly searching for spilt grain. The amount of spilt grain declined from around 80kg/ha when the sheep were introduced to approximately 20kg/ha when they were removed (Figure 3).
Very little green pick was available during the grazing period and as a result they lost condition over this time. There also appeared to be a change in animal behaviour, with an approximate five per cent decrease in daily time spent grazing when spilt grain levels dropped to around 40kg/ha. There may be some value in using this type of data (assuming it could be delivered in real-time) for managing livestock in stubbles where the feed value of spilt grain is difficult to determine.
WINTER GRAZING
Grazing intensity was much more spatially variable on the sown vetch pasture in winter than on the cereal stubble in summer. Figure 4 shows that the sheep concentrated grazing on the western end of the paddock during the first 10 days after which paddock utilisation by the livestock slowly increased over time. However, during any 10-day period, livestock spent 50 per cent of the time grazing only 25 per cent of the paddock. The remaining 25 per cent was not grazed.
Spatially variable grazing led to under-utilisation of pasture on the eastern end of the paddock. Figure 5 shows vetch dry matter accumulation at two of the 29 monitoring locations. On the western edge (site 12), dry matter did not accumulate between the first four monitoring dates, probably because grazing intensity matched pasture growth rate. However, on the eastern end of the paddock (site 16) dry matter accumulated at a consistent rate and when the sheep were removed, approximately 2.5t/ha vetch still remained. This represents a significant under-utilisation of the feed base with a subsequent loss of potential income from either increased stocking rates or harvest of the excess feed for fodder.
COMMERCIAL PRACTICE
Farmers already recognise that livestock graze large Mallee paddocks unevenly, but this project began to put some hard numbers on the extent of the variability in spatial paddock utilisation. During summer, when feed was limiting, the paddock was fully utilised, but sheep spent about 40 per cent of their time grazing just 25 per cent of the paddock. This means that large areas were very lightly grazed, with animals travelling long distances across the field.
This contrasted with the winter grazing period in which sheep concentrated 50 per cent of grazing on 25 per cent of the paddock. A further 25 per cent of the paddock was left unutilised.
Currently there is no easy solution to overcoming this problem. Management actions such as moving water points, increasing mob sizes and rotating sheep in and out of paddocks regularly are likely to improve paddock utilisation but are not likely to fully resolve the issue. Rapid fencing systems such as portable electric fencing have been used effectively by some Mallee farmers, but require resources to erect and dismantle. The development of such new technologies as virtual fencing could drastically improve the utilisation of large Mallee paddocks and the data from this project can start making an economic case for investing in more flexible fencing technologies.
ON-FARM PROFITABILITY
During the winter grazing phase, livestock were removed from the paddock due to low groundcover on its western end, while a considerable amount of feed was left under-utilised on a quarter of the paddock. Two hundred ewes with lambs at foot were grazing the paddock, or 5.6 Dry Sheep Equivalent (DSE) per hectare. However, as grazing occurred on only 75 per cent of the paddock, the stocking pressure on the utilised part of the paddock was 7.3DSE/ha.
It is logical that, with improved grazing management (such as with portable electric fencing), an additional 65 ewes with lambs could have been fed.
Alternatively, a quarter of the paddock could have been cut for hay. If 1.5t/ha of vetch hay were cut from 25 per cent of the paddock, an additional $153/ha of profit would have been made on a quarter of the paddock or the equivalent of approximately $4000 additional profit.
ACKNOWLEDGEMENTS
This project is supported by Mallee Catchment Management Authority, Mallee Sustainable Farming, University of New England and BCG through funding from the Australian Government’s National Landcare Programme. The GRDC-funded Grain & Graze 3 initiative provided additional support.
