Methane emissions in pasture-based systems with contrasting intensification strategies in Uruguay in two periods: operational simplicity vs maximised productivity

Abstract

Meeting the growing demand for high-quality animal protein while minimising environmental impact is a major challenge for dairy systems. In Uruguay, where livestock production accounts for roughly 73% of national greenhouse gas (GHG) emissions, mainly from enteric methane (CH₄), pasture-based dairy systems must adapt to align with sustainability goals. This study evaluated whether two pasture-based dairy systems with contrasting intensification strategies could maintain low CH₄ emissions while sustaining productive efficiency. A low-input, operationally simple system (OS) with a stocking rate of 1.8 livestock units per hectare (LU/ha) was compared with a higher-input, productivity-oriented system (HP) at 3.0 LU/ha. Both systems were based on perennial pastures of similar botanical composition and managed under structured rotational grazing. Enteric CH₄ emissions were measured during winter and spring 2023 in 24 Holstein and Holstein × Jersey cows (12 per system), using the sulphur hexafluoride (SF₆) gas-tracer technique. Milk yield and diet composition were also evaluated. Despite the higher stocking rate (SR) and greater annual milk yield in the HP system (10 106 vs 7 262 kg of milk per hectare), daily methane emissions per cow (280 g CH₄/cow per day) and CH₄ emission intensity corrected per kg of fat and protein corrected milk (FPCM) were similar between systems (11 g CH₄/kg FPCM, on average). However, CH₄ emissions per hectare were higher in the HP system (9.1 vs 6.8 kg CH₄/ha per day), reflecting the impact of the higher SR on total emissions. When compared with values commonly reported for pasture-based dairy systems (10 – 21 g CH₄/kg FPCM), both systems were at the lower end of this range for CH₄ intensity. These findings suggest that well-managed pasture-based dairy systems can sustain different intensification strategies without compromising environmental performance. However, continued efforts are needed to improve resource use efficiency and further reduce total greenhouse gas emissions.