Discovering the Link Between Lamb Weaning Weights and Farm Success

New Zealand's sheep and beef sector stands as a cornerstone of the nation's agriculture, contributing significantly to exports and rural economies. Recent research from Massey University sheds light on a straightforward yet powerful strategy for farmers: targeting higher lamb weaning weights. This approach not only elevates farm profitability but also enhances emissions efficiency, offering a win-win in an era where sustainability is paramount.

The study, conducted by PhD candidate Joseph Adjabui and a team of esteemed supervisors including Emeritus Professor Steve Morris, Professor Patrick Morel, Professor Peter Tozer, Associate Professor Ramilan Thiagarajah, and Professor Paul Kenyon, models real-world scenarios on a typical North Island hill country farm. By simulating increases in lamb weaning weights under fixed feed supplies—mirroring New Zealand's pasture-based systems—the researchers reveal compelling outcomes for productivity and environmental impact.

Understanding Lamb Weaning in New Zealand Sheep Farming

Lamb weaning refers to the process of separating lambs from their mothers, typically around three to four months of age when lambs reach 20 to 25 kilograms liveweight. In New Zealand, where sheep farming dominates hill country landscapes, weaning timing and weight directly influence growth trajectories, ewe recovery, and overall flock performance.

Traditional practices prioritize high lambing percentages, but emerging evidence suggests focusing on heavier individual lambs yields superior results. Beef + Lamb New Zealand recommends a minimum weaning weight of 16 kilograms for early weaning, provided high-quality legume-based pastures are available. Factors like ewe nutrition during lactation, pasture quality, genetics, and parasite control play crucial roles in achieving these targets.

The Methodology Behind Massey's Groundbreaking Model

Researchers employed a system dynamics bioeconomic model to evaluate three scenarios on a representative North Island sheep and beef farm: a base system, a 10% increase in weaning weight, and a 20% increase. Fixed feed availability was assumed, reflecting limited supplementary feeding common in pasture-reliant operations. Ewe numbers were adjusted slightly downward in higher weaning scenarios to balance feed demand.

The model incorporated productivity metrics such as lamb carcass weight per hectare, cash operating surplus, and predicted enteric methane emissions—the primary greenhouse gas from ruminant digestion. This holistic approach integrates biological, economic, and environmental factors, providing actionable insights for farmers.

Productivity Gains from Heavier Weaning Weights

One of the most striking results was the boost in lamb carcass weight sold per hectare. In the 10% weaning weight increase scenario, this metric rose by approximately 2%, escalating to 14% in the 20% scenario compared to the base. Heavier lambs finish faster, reaching slaughter weight sooner and allowing more efficient land use.

Additionally, the proportion of lambs meeting prime specifications post-weaning jumped from 60% in the base to 84% in the 20% scenario. This shift means more lambs qualify for premium markets, enhancing revenue streams without expanding flock sizes or inputs.

Boosting Profitability Without Added Costs

Financial outcomes were equally promising. Cash operating surplus—the key profitability indicator—improved by 6% with a 10% weaning weight lift and soared 51% in the 20% scenario. These gains stem from system efficiencies: shorter time on farm reduces feed consumption, animal health interventions, labor, and shearing costs.

Emeritus Professor Steve Morris explains, "The most efficient lamb is the one sold directly to slaughter at weaning. It has been alive for fewer days, eaten less feed and required fewer animal health treatments, less labour and no shearing." Redirected feed supports other stock classes, amplifying overall farm performance. For more on the study, see the Massey University announcement.

Photo by Muhammad Faiz Zulkeflee on Unsplash

Emissions Efficiency: A Path to Sustainability

Total greenhouse gas emissions remained stable across scenarios due to balanced ewe numbers and fixed feed. However, predicted enteric methane emissions per kilogram of product declined by 1.8% (10% scenario) and 3.6% (20% scenario). Economic emissions efficiency also rose, decoupling production growth from environmental impact.

Joseph Adjabui notes, "These results show there is no trade-off between profitability and emissions efficiency under this system." New Zealand's sheep sector already boasts one of the world's lowest carbon footprints—around 15 kg CO2e per kg lamb—but these strategies align with national goals to reduce agricultural methane by 24-47% by 2050. Detailed findings appear in the Journal of the Australian Grassland Association.

Practical Steps for Farmers to Achieve Higher Weaning Weights

• Optimize ewe lactation: Ensure ewes enter lambing in body condition score 3.0-3.5 with high-quality pasture (11+ MJ ME/kg DM).
• Monitor pasture cover: Maintain rotation lengths for 1500-1800 kg DM/ha pre-grazing.
• Select genetics: Choose rams with high weaning weight estimated breeding values (EBVs).
• Control parasites: Implement targeted drenching based on fecal egg counts.
• Consider supplements: Use legume mixes or limited maize grain if pasture growth lags.

Early weaning at 16+ kg LW on herb-clover pastures can accelerate ewe recovery while sustaining lamb growth.

Challenges and Considerations in Implementation

While promising, hurdles exist. Professor Paul Kenyon cautions that earlier finishing conflicts with the industry's need for year-round lamb supply to meet export demands. Pasture variability, especially in hill country, demands vigilant management. Genetic shifts toward heavier weaning weights may take generations, requiring long-term ram selection.

Financial risks include initial investments in genetics or supplements, though models show rapid returns. Climate variability exacerbates feed shortages, underscoring the need for resilient systems. For real-world application, see coverage in Rural News Group.

Massey's Legacy in Sheep Research

Massey University's School of Agriculture and Environment, led by Professor Paul Kenyon, has long pioneered sheep husbandry innovations. The International Sheep Research Centre has delivered breakthroughs in early weaning, herb mixes, and reproductive efficiency, benefiting farmers nationwide. Supervisors like Emeritus Professor Steve Morris bring decades of expertise in pastoral systems.

This study builds on prior work, such as bioeconomic modeling of lambing percentages versus growth rates, reinforcing Massey's role in sustainable agriculture.

Broader Implications for New Zealand's Agri-Emissions Landscape

Sheep and beef farming accounts for about 44% of NZ's agricultural emissions, predominantly methane. With production stable since 1990 despite 30% emissions drop, efficiency gains like these are vital for He Waka Eke Noa—the partnership pricing framework. Globally competitive footprints position NZ lamb favorably amid consumer sustainability demands.

Photo by Aditya Chinchure on Unsplash

Future Directions and Industry Outlook

Upcoming research may explore genetics, precision feeding, and climate-resilient pastures to amplify these benefits. Collaborative trials with Beef + Lamb NZ could validate models on commercial farms. Policymakers might incentivize weaning weight targets via emissions trading.

For farmers, integrating these insights promises resilient operations amid volatile markets and climate pressures. Massey's work exemplifies how university research drives practical, profitable sustainability.