School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe feasibility of adopting 1-year-old lambing systems in commercial Merino flocks of south eastern Australia( 2013)This study tested the hypothesis that under ‘best-practice’ management, lambing Merino ewes as 1-year-olds can be more profitable than maiden lambing as 2-year-olds. The study comprised 3 major research components: 1. The use of production system modelling to investigate additional inputs required in 1-year-old lambing systems; 2. An economic analysis of 1-year-old lambing system adoption and risk analysis based on modelled outputs; and 3. Commercial trials of 1-year-old lambing systems to assess reproductive performance as 1-year-olds and impacts on performance at subsequent joining. The modelling tool GrassGro® was used to predict additional supplementary feeding requirements of 1-year-old lambing systems when managed according to ‘best-practice’ live weight profiles. Model simulations included 3 production locations in south eastern Australia and additional simulation variables at each location including: 2 pastures types (Typical and Lucerne-based); and 3 stocking rates (‘low’, ‘moderate’ and ‘high’). All production systems were modelled over 40 years based on historical climatic records at each location. Across the 18 equivalent production systems modelled, mean supplementary feed requirements were between 24 and 116 kg greater per replacement ewe in 1-year-old lambing systems compared with conventional 2-year-old lambing systems. The greater supplement requirements were also associated with larger variation in annual quantities indicating higher production risk in 1-year-old lambing systems. Annual Marginal Rates of Return (MRR) were calculated for 1-year-old lambing system adoption based on the simulated outputs of modelled systems. A broad range of production/price scenarios were investigated including: supplementary feed price ($150, $250 and $350/t as-fed); weaner lamb value ($40, $60 and $80/head net); and 1-year-old ewe weaning rates (0.3, 0.5 and 0.7 lambs per ewe joined). Across equivalent production systems, annual MRR from 1-year-old lambing system adoption ranged from -80 to >1000% for the various production/price scenarios tested. To assess the risk of system adoption, the proportion of years that investment in 1-year-old lambing exceeded Target Rates of Return (TRR) of 16% and 50% was determined. Probability of achieving 16 and 50% TRR was highly sensitive to altered production/price scenarios, although between production systems there were large differences in their capacity to maintain high levels of probability. Probability of achieving TRR in Hamilton production systems were generally more resilient to increases in supplementary feed price and reductions in weaner lamb value and weaning rate. Low stocking rate Lucerne pastures had consistently higher probability of achieving TRR, while high stocking rate Lucerne pastures generally generated the lowest probabilities compared with other production systems at each location. Commercial trials of 1-year-old Merino lambing systems were undertaken to evaluate ewe reproductive capacity at first and subsequent joining when managed to ‘best-practice’ guidelines. Reproductive performance of commercial Merino ewes at first joining (8-9 months of age) included lamb marking rates of 72 and 75%. Pregnancy scanning rates following subsequent joining (19-20 months of age) were 131 and 132%. At one trial site pregnancy scanning results were higher in previously pregnant ewes compared with previously non-pregnant ewes (138 v. 118%), while at the other site they were lower (129 v 144%). Interviews with trial site producers were also conducted to gain first-hand insight into management issues with 1-year-old lambing systems, perceived benefits, costs and business risks. Modelling of 1 and 2-year-old lambing systems in this study suggests that given the right combinations of lamb value, supplementary feed price and reproductive performance, adoption of 1-year-old lambing systems has a high probability of generating increased annual profits across a range of production locations in south eastern Australia. The analysis also suggests that pasture type and stocking rate prior to 1-year-old lambing system adoption will have a strong bearing on the likelihood of improved profits. Commercial trials of 1-year-old lambing systems provide evidence that weaning rates in excess of 70% are possible in Merino ewes joined at 8-months-of-age in natural breeding programs. There were conflicting results on the effects of pregnancy on reproductive performance at subsequent mating which may be attributable to live weight differences between ewe groups at each site. On the balance this study supports the view that lifetime productivity of ewes should not be compromised by lambing as 1-year-olds provided ewes achieve appropriate body weights by subsequent joining.