Access to Emission Control Blocks for improved productivity and mitigation of enteric methane in smallholder cattle in Cambodia

Context Livestock raising is important in Cambodia, with an estimated 3.4 million cattle located in 780,000 smallholder farming households. However, productivity is low, constrained by poor animal nutrition, health and management. Aims This study examined supplementation of cattle with 20 kg ‘Emission Control Blocks’ (ECB, AgCoTech Laos) to test for improved growth rates and reduced enteric methane production. Methods Smallholder farmers (n = 40) within two villages in Pursat Province each provided two age- and weight-matched local breed cattle (n = 80). One animal from each of the 40 farms was designated ‘treatment’ and accessed the ECB for a 10-week period, with ‘control’ animals denied access. To assess production impacts and estimate methane emissions, regular measurements included body weight by tape to calculate average daily gain (ADG), body condition score (BCS), and ECB consumption rates. Trial results were used to model methane emissions using the Intergovernmental Panel on Climate Change (IPCC) Tier 2 calculator. Additionally, at the end of the trial, breath methane concentration was measured by a handheld methane monitor in both groups, enabling a recording of breath methane abatement. Key results The average body weight of the ‘treatment’ cattle increased by 5.31 kg (ADG of 76 g/day) compared to 2.97 kg (ADG of 42 g/day) in ‘control’ animals that completed the trial, a significant difference (P < 0.05). A ‘dose-response’ effect of ECB consumption was observed, with increased body weight by 0.33 kg/kg ECB consumed in the first 5 weeks (P = 0.036), increasing to 1.33 kg/kg ECB consumed in the second 5-week period (P < 0.001). No differences in BCS between groups were observed. Modelling using IPCC inventory software indicated the block reduced carbon dioxide equivalent (CO2e) of emissions from a baseline of 1320 kg to 1100 kg per annum. The effect of ECBs (P = 0.0019) on enteric or breath methane concentration was confirmed, with ‘treatment’ producing an average estimated 88.0 g/day compared with 106.0 g/day for ‘control’, a 17.0% decrease in daily methane production, extrapolated to 184 kg CO2e per annum. Conclusions These findings occurred despite lower ECB consumption rates than expected, attributed to excessive hardness of this batch of blocks. ECBs offer both productivity gains and enteric methane abatement in cattle. Implications If widely available, use of ECBs may support Cambodia in meeting Nationally Determined Contributions and the Global Methane Pledge.