Increasing lamb weaning weights linked to emissions efficiency and improved profitability

The research, led by PhD candidate Joseph Adjabui at Te Kunenga ki Pūrehuroa Massey University, examined how higher lamb weaning weights affect productivity, profitability and predicted enteric methane emissions (methane produced during digestion). While previous studies have focused on the production and financial benefits, this research also considers greenhouse gas outcomes, an increasingly important factor in farm systems decision-making.

Using a system dynamics bioeconomic model, the study analysed a North Island hill country sheep and beef farm under three scenarios: a base system, a 10 per cent increase in weaning weight and a 20 per cent increase.

The modelling assumed a fixed feed supply, reflecting typical New Zealand pasture-based systems with limited supplementary feeding.

The results showed consistent improvements in farm performance as weaning weight increased.

Lamb carcass weight sold per hectare increased by approximately two per cent under the 10 per cent scenario, and 14 per cent under the 20 per cent scenario, relative to the base system. Cash operating surplus also improved, increasing by around six per cent and 51 per cent respectively.

Mr Adjabui says the gains were driven by improved system efficiency rather than increased inputs.

“Heavier lambs at weaning meant more kilograms of lamb could be produced and sold earlier, improving both total production and farm income.”

The proportion of lambs meeting prime specifications soon after weaning also increased, reaching 84 per cent under the 20 per cent scenario compared with 60 per cent in the base system.

Because total feed supply was fixed, ewe numbers were adjusted slightly downward to balance demand, helping keep total emissions broadly stable. Predicted enteric methane emissions declined marginally from the base scenario as weaning weights increased.

While total emissions remained similar, emissions per kilogram of product improved, decreasing by approximately 1.8 per cent under the 10 per cent scenario and 3.6 per cent under the 20 per cent scenario. Economic emissions efficiency also increased.

“These results show there is no trade-off between profitability and emissions efficiency under this system,” Mr Adjabui says.

One of the key drivers of improved performance is earlier finishing. Increasing weaning weight allows lambs to reach slaughter weight sooner, reducing time on farm, improving feed use efficiency and lifting overall system output.

PhD supervisor Emeritus Professor Steve Morris says the efficiency gains from earlier-finished lambs are clear when viewed at a whole-farm level.

“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,” he explains.

“That feed is then available for other stock classes, improving overall farm performance. It is also often sold when prices are strongest, before peak seasonal supply.”

However, Head of School of Agriculture and Environment Professor Paul Kenyon notes there is a wider industry consideration.

“While earlier finishing improves profitability at farm level, the industry also relies on a steady year-round supply of lamb to meet export demand, which is a conflict.”

Mr Adjabui’s research was supervised by Emeritus Professor Steve Morris, Professor Patrick Morel, Professor Peter Tozer, Associate Professor Ramilan Thiagarajah and Professor Paul Kenyon at Massey University.