Grassland systems of red meat production: integration between biodiversity, plant nutrient utilisation, greenhouse gas emissions and meat nutritional quality.

摘要

Government policies relating to red meat production take account of the carbon footprint, environmental impact, and contributions to human health and nutrition, biodiversity and food security. This paper reviews the impact of grazing on these parameters and their interactions, identifying those practices that best meet governments' strategic goals. The recent focus of research on livestock grazing and biodiversity has been on reducing grazing intensity on hill and upland areas. Although this produces rapid increases in sward height and herbage mass, changes in structural diversity and plant species are slower, with no appreciable short-term increases in biodiversity so that environmental policies that simply involve reductions in numbers of livestock may not result in increased biodiversity. Furthermore, upland areas rely heavily on nutrient inputs to pastures so that withdrawal of these inputs can threaten food security. Differences in grazing patterns among breeds increase our ability to manage biodiversity if they are matched appropriately to different conservation grazing goals. Lowland grassland systems differ from upland pastures in that additional nutrients in the form of organic and inorganic fertilisers are more frequently applied to lowland pastures. Appropriate management of these nutrient applications is required, to reduce the associated environmental impact. New slurry-spreading techniques and technologies (e.g. the trailing shoe) help reduce nutrient losses but high nitrogen losses from urine deposition remain a key issue for lowland grassland systems. Nitrification inhibitors have the greatest potential to successfully tackle this problem. Greenhouse gas (GHG) emissions are lower from indoor-based systems that use concentrates to shorten finishing periods. The challenge is to achieve the same level of performance from grass-based systems. Research has shown potential solutions through the use of forages containing condensed tannins or establishing swards with a high proportion of clover and high-sugar grasses. Relative to feeding conserved forage or concentrates, grazing fresh grass not only reduces GHG emissions but also enhances the fatty acid composition of meat in terms of consumer health. It is possible to influence biodiversity, nutrient utilisation, GHG emissions and the nutritional quality of meat in grass-based systems, but each of these parameters is intrinsically linked and should not be considered in isolation. Interactions between these parameters must be considered carefully when policies are being developed, in order to ensure that strategies designed to achieve positive gains in one category do not lead to a negative impact in another. Some win-win outcomes are identified.