Traditional vs modern: Role of breed type in determining enteric methane emissions from cattle grazing as part of contrasting grassland-based systems

Ruminant livestock turn forages and poor-quality feeds in to human edible products, but enteric methane (CH4) emissions from ruminant livestock are a significant contributor to greenhouse gases (GHGs) and hence to climate change. Despite the predominance of pasture-based beef production systems in many parts of Europe there is little data available regarding enteric methane emissions from free-ranging cattle grazing. This study investigated the role of breed type in influencing CH4 emissions from growing beef steers managed on contrasting grasslands typical of intensive (lowland) and extensive (upland) production systems. Using the SF6 dilution technique CH4 emissions were estimated for a modern, fast-growing crossbred (Limousin cross) and a smaller and hardier traditional breed (Welsh Black) when grazing perennial ryegrass (high nutritional density, low sward heterogeneity) and semi-improved hill pasture (low/medium nutritional density, high sward heterogeneity). The live-weight gain of the two breed types was similar and there was no effect of breed type on the amount of CH4 emitted when grazing the ryegrass pasture. When grazing the hill sward the growth rates were substantially lower, and although breed type did not influence live-weight gain when grazing this pasture type, the modern breed emitted significantly more CH4 than the traditional breed. While emissions per unit feed intake were similar for the lowland and upland systems, CH4 emissions per unit of live-weight gain were substantially higher when the steers grazed the poorer quality pasture and the results indicate that breed type has the potential to influence CH4 emissions when cattle graze such swards. However, overall any effects of breed type were relatively small relative to the combined influence of pasture type and location.