AS the 2019 lambing season approaches, research has proven it is worth re-examining ewe mob size in order to improve lamb survival rates.
Murdoch University researcher Amy Lockwood has been investigating the relationship between lambing density and lamb survival, finding smaller mob sizes improve marking percentages.
Data was collected between 2016 and 2018 from Merino and non-Merino breeds across southern Australia to investigate the survival of both single and twin born lambs.
Three experiments were conducted as part of a national study funded by Australian Wool Innovation (AWI) and Meat and Livestock Australia (MLA), with research sites at 85 properties across WA, South Australia, Victoria and New South Wales, bolstered by survey data also provided by 194 sheep producers.
When the research project commenced, it was expected that smaller mob sizes and stocking rates would increase lamb survival based on findings from survey data collected in South-East Australia.
The national project found reducing mob size improved lamb survival rates, but reducing stocking rates did not, showing that it is the number of ewes lambing per day which drives the impact of lambing density on lamb survival.
On average, the research demonstrated that reducing mob size at lambing by 100 ewes will increase the survival of single-born lambs by 0.8 per cent and twin-born lambs by 2.2pc, regardless of breed and stocking rate when ranging from 0.5 to 12 ewes per hectare.
"We expect that greater lamb survival in smaller mobs is associated with a reduced risk of mismothering, particularly in twin mobs where twice as many lambs are born" Dr Lockwood said.
The impact of mob size on lamb survival was not found to be influenced by ewe condition score (average 3.1) or feed-on-offer (FOO) at lambing across the national project.
However, findings from additional work completed as part of Dr Lockwood's PhD research suggested potential effects of FOO and supplementary feeding.
"This requires more work but the findings from my PhD suggested that the impact of mob size on lamb survival may be greater when FOO is limited and ewes are supplementary fed during lambing," Dr Lockwood said.
"This indicates that there could be greater benefits of reducing mob size when lambing in autumn or under tight seasonal conditions."
The project also highlighted additional long-term benefits of improved pasture utilisation if paddocks were permanently subdivided in order to split larger lambing mobs.
"There is a complementary benefit of reduced mob and paddock size on increased pasture utilisation," she said.
"Smaller paddocks limit selective grazing which means there is the opportunity to increase stocking rates and improve the utilisation of available FOO."
Beyond looking at survival rates, the project also included economic modelling to determine the pay-off associated with splitting mobs by subdividing paddocks or reallocating mobs within the lambing paddocks currently available on the farm.
"It is important to note that numerous factors influence the optimum mob size for lambing, including stocking rate, ewe pregnancy status, whether paddocks are temporarily or permanently subdivided, the desired return on investment, breed and lamb price.
"Optimum mob sizes will therefore vary between enterprises and this is why there is no generic mob size recommendation for lambing."
However, the economic modelling demonstrated that the optimum mob sizes for most enterprises are lower than those which are currently recommended to industry for adult ewes, being 400-500 single-bearing ewes and 100-250 twin-bearing ewes.
The project found that there is greater economic return from reducing mob and paddock size at lambing for twin-bearing ewes compared to single-bearing ewes, therefore smaller paddocks should be prioritised for twins.
Looking at fencing costs within the economic modelling work, Dr Lockwood said the research found temporary fencing was a cost-effective way to reduce mob size but the long-term benefits of improved pasture utilisation and subsequently higher stocking rates will only be capitalised when paddocks are subdivided permanently.
Dr Lockwood said the response to the project from sheep producers across the country was great.
"I have had feedback from a number of producers who have begun subdividing paddocks and lambing ewes in smaller mobs to continue to improve marking rates" she said.
Lamb mortalities represent a major source of reproductive wastage and are estimated to cost the Australian sheep industry more than $1 billion each year, based on current lamb prices so looking to the future, Dr Lockwood said research related to lamb survival will continue to be important.
"Improving lamb survival is complex because there are so many factors influencing lamb survival," she said.
"Ongoing work is aimed at adding to the current 'tool package' by providing additional guidelines to help farmers increase marking rates."
This research was funded by AWI and MLA and involved collaborators from Murdoch University, Agriculture Victoria, Landmark, Elders, University of Adelaide, the New South Wales Department of Primary Industries and Shearwell Australia.
