Pelletier N, Pirog R, Rasmussen R (2010). "Comparative life cycle environmental impacts of three beef production strategies in the Upper Midwestern United States", Agricultural Systems 103 (2010) 380–389  This paper compares three US beef rearing systems. Cattle are finished either in: feedlot systems (having received hormone implants); backgrounding systems (also with hormone implants); or on pasture (no implants).

In November 2009 the World Watch Institute released a report arguing that the FAO's estimate of livestock's total contribution to global GHG emissions (18%) is a serious underestimate and that the true footprint of livestock production is around 51% higher.