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).
The paper describes briefly what backgrounding is but for another explanation see attached below. In each case the cow-calf stage was the same (i.e. all calves that went on to become beef animals were born and reared, to the point of weaning, in the same way). The study compares the following:
- GHG emissions per herd and unit of beef produced
- ecological footprint/land take (this is weighted so arable scores differently from pasture land)
- industrial energy in (i.e. fossil fuels) vs edible energy out (meat)
- chemical energy in (biomass energy for consumption) vs edible energy out (meat)
- edible energy in (grains etc) vs edible energy out (meat)
It finds on a per kg meat basis that feedlot cattle score best in terms of: GHG emissions per herd and unit of beef produced; ecological footprint/land take (this is weighted so arable scores differently from pasture land); industrial energy in (i.e. fossil fuels) vs edible energy out (meat); and chemical energy in (biomass energy for consumption) vs edible energy out (meat). They score worst on the edible energy in vs edible energy out indicator. Pasture finished animals do worst, except on the edible energy in vs edible energy out when they do much better. The paper assumed no carbon sequestration occured in pasture-fed systems. However, it also carried out a sensitivity analysis and when it applied estimates of 0.12 tonnes C sequestered/ha/year for improved cow–calf pastures and 0.4 tonnes C sequestered/ha/year for previously unmanaged pastures subjected to management-intensive grazing for pasture finishing, it found that pasture raised beef have 15% lower emissions than the feedlot beef and better than the backgrounded ones too. In other words, assumptions about sequestration are key. Of course, as the paper notes, as soil carbon equilibrium is reached the benefits tail off. In terms of industrial (i.e. fossil energy) in vs fossil energy out, the paper points out that the pasture receives applications of fertiliser and is managed with use of tractors and so forth. It points out that ‘beef produced on unmanaged rangeland may, indeed, be considerably less energy intensive than the systems we modelled, although this would also result in tradeoffs in terms of animal performance and associated emissions'. In terms of chemical energy in, this is the description in the paper: ‘Since the chemical energy content of biological materials represents a crude but reasonable proxy for the limited net primary productivity underpinning almost every trophic web, gross energy return on investment provides a reasonable first-order approximation of the ecological efficiency with which our food systems supply food energy relative to the demands they place on ecological communities’. I think what the paper is comparing is essentially caloric energy from grains as opposed to those from byproducts. For a given byproduct emissions generated during the course of producing a product are allocated on the basis of the respective caloric energy content of the co-product streams. So for instance in the case of citrus if the orange flesh contains 50 calories and the pith/peel 10 (at a guess), and the pulp goes to animal feed, then one sixth of the emissions generated during the course of producing that orange is allocated to the pith/peal and hence to the animal. Since grains are more digestible than byproducts (and so less feed input is wasted in the form of methane), it does in fact stand to reason that it is more efficient to feed them these than byproducts. And one supposes that if it is inefficiently consumed by beef cattle there is relatively less available for other life forms. Of course, one might ask what else you would do with these byproducts if you didn’t feed them to animals (anaerobic digestion is one answer). You could also say that the pith and peel of an orange is not the driver of citrus production – the flesh is. But these are value judgements and the point here was to look at physical flows of materials and energy. On ecological footprinting/land take the study says: 'Although the footprint method weights pasture and cropland differently (because pasture provides a greater range of ecosystem services than does cultivated cropland), the large areas required ultimately contribute to a larger ecological footprint for grass-finished versus feedlot finished beef. Note that the ecological footprint includes not just the area used for the livestock but also the area needed to offset the emissions they produce. The paper shows that the cow–calf phase is the greater contributor to resource use and emissions in beef production. Averaged across impact categories, the cow–calf phase is responsible for approximately 63% of impacts per live-weight kg of beef produced in all three of the finishing scenarios. As the paper points out (and as others have too) this rearing of specialised beef animals and dairy mothers is very wasteful since the beef mother hangs around producing emissions and doing nothing else except produce a calf once a year. The dairy cow on the other hand, produces lots of milk but the male calves aren’t very good for beef and are often shot at birth. Dual breeds, when the mother also produces milk, means you get the impacts shared between the dairy and the beef sectors. It would be interesting to do the study in a UK context, where hormone use is not permitted. Finally, the paper concludes with the following points: “We would also stress that none of the systems analyzed can be described as ecologically efficient relative to most other food production strategies. Certainly, our measures of resource returns on investment provide strong indications to the contrary. Moreover, our work does not provide insights into the social and economic dimensions of these activities. For example, we do not consider costs and benefits related to variables like job creation or quality of life, nor do we address a spectrum of proximate ecological considerations, including biodiversity impacts, or concerns such as animal welfare. Our results should therefore not be taken as stand-alone metrics of the sustainability of feedlot versus pasture-finished beef production in the US Upper Midwest. Rather, they are intended to contribute to our necessarily evolving and increasingly nuanced understanding of beef production and food system sustainability issues generally, and offer insights into how the beef production systems considered here might best pursue improved environmental performance.”