Improving lamb survival by optimising lambing density (ON-00347 /4500007573)

Summary

The National Sheep Reproduction Strategy estimated that improving the survival of single lambs by 5% and twin lambs by 20% would improve farm profit across the industry by $100M and $350M per annum. However, there is a major gap in knowledge surrounding the effects of mob size and stocking rate on lamb survival.

A limited number of studies conducted on a small, experimental scale have suggested that higher stocking rates or lambing densities increase the risk of mismothering, ewe-lamb separations and lamb mortality. Lambing density is expected to have a greater effect on the survival of multiple-born lambs because more lambs are born per day which presents a greater risk for mismothering.
 
This project aimed to quantify the effects of mob size and stocking rate on the survival of Merino and non-Merino lambs born across southern Australia to deliver improved recommendations for sheep producers regarding the allocation of ewes to mobs and paddocks at lambing. This project also aimed to assist producers to make more informed decisions about the cost-benefit of investing funds in paddock subdivision through permanent or temporary fencing to improve reproductive performance and farm profitability.

The research involved three components which were completed across southern Australia;

1. on-farm research at 70 commercial farms to test a 2x2 factorial combination of mob size (high or low) and stocking rate (high or low) on the survival of twin-born lambs of Merino or non-Merino breed;
2. on-farm research at 15 commercial farms to test the effect of mob size (high or low) on the survival of twin-born Merino lambs at low stocking rates; and
3. a network of 194 sheep producers who contributed data for 2174 lambing mobs from their own farms to investigate the impacts of mob size and stocking rate on the survival of single- and twin-born lambs of Merino and non-Merino breed across a broad range of management and environmental conditions.
    

Lamb survival was found to be poorer at higher mob sizes but not stocking rates. Analysis of the data collected from producers across southern Australia showed that the survival of single- and twin-born lambs decreased by 0.3% and 1.1% per additional 100 ewes in the mob at lambing, regardless of Merino or non-Merino breed. Economic modelling showed that reducing mob size at lambing is justified even if paddock subdivision is required. The economic return from reducing mob and paddock size at lambing is greater for twin- compared to single-bearing ewes, with the optimum mob size for twin-bearing ewes being 40% to 50% that for single-bearing ewes.
 
This project was co-funded by AWI and MLA.