In February 2008, DEFRA published a report online called 'The environmental impact of livestock production - review of research and literature'. The executive summary of the report says: '... The main domestic livestock sectors produce a wide range of products (food, leather, wool etc) and public services, such as employment, landscape and cultural heritage. However, livestock production impacts on the environment in a variety of ways, both positive and negative, but there are some systems where there is greater potential for the environment to be compromised in order to achieve efficient production. The key is to minimise negative impacts in the most cost-effective way ...' The review is divided into two parts, ie industry (five sectors: dairy, beef, sheep, pigs, poultry) and then environmental impact (four areas: soil, water, air, biodiversity).
The report is worth reading, if only to see how misguided DEFRA is.
You can read the review online at www.defra.gov.uk/farm/livestock/pdf/envimpacts-livestock.pdf