Sustainability Metrics

By Research Officer, Charlotte Wheeler

Sarah Hall wrote an excellent primer on the value of more holistic methods of assessing sustainability on farms, using the Global Farm Metric as an example (see link here). In this post, I’m going to dig into the trade offs at play when we decide to favour one metric of sustainability over another, or indeed several. 

(Lynbreck Croft, Scottish Uplands)

At a work event a few weeks ago I overheard someone say that the reason they support a large-scale transition to plant-based diets is because of two concerns; methane, and land use. Leaving aside the intricacies of that particular debate for now, I was struck by this framing. I realised that I have the same tendency; I support (some forms) of livestock farming because of specific metrics, although mine are an interest in biodiversity and the development of low-fossil fuel food production. Depending on the evidence you look at, and your priorities, you can end up with vastly different recommendations in the pursuit of a sustainable food system.

All too often, the “sustainability” of a business or product is determined according to a single metric, such as greenhouse gas (ghg) emissions. But when farmers are incentivised to design their farm systems around one metric, it almost inevitably leads to perverse outcomes. An example of this can be seen in Sainsbury’s Low-Carbon Beef range, which reports a 25% reduction in carbon emissions over the life cycle of the animal (1). These savings are achieved as a result of Sainsbury’s “Game Changer” system, which they have developed in association with ABP (2), wherein farmers are incentivised and supported to finish cattle by 20 months of age, faster than industry average. By finishing cattle in a shorter amount of time, they emit fewer emissions over their lifetime for the same volume of meat. Sainsbury’s are proud of their system, and I’m sure their farmers are too; according to this metric they are exceeding industry standards and leading the way to Net Zero in the farming industry. However, if sustainability were evaluated according to a wider range of metrics, these farms might not measure up as highly. 

Intensive cattle finishing systems here in the UK tend to feed their stock on a range of products in addition to conserved forage such as hay or silage, and pasture (if they have access to grazing). Unless the animals are 100% grassfed, they will gain a significant proportion of their diet from feeds like straight cereal grains, concentrate feed, or by-products or waste products. These last two can include a huge range of things, including spent brewers grains, by-products from oilseed processing, crop residues, or food items that aren’t suitable for retail, such as bread or broken biscuits from factories (3)

Even within one metric, there are a range of ways to define and measure it, leading to different outcomes; for example, some calculations wouldn’t include the carbon emissions associated with waste products precisely because they are considered waste, whereas a dedicated livestock concentrate feed would be included in measurements. Although fattening cattle on food waste can seem like a neat solution to two issues, this belies the fact that more emissions would have been saved if wasted food wasn’t produced in the first place. We should be cautious of “valorising” food waste as a result of its various beneficial uses, at risk of building dependency into our system; a 2020 report from Feedback estimated that while utilising food waste as animal feed saves on average three times more emissions than sending it to anaerobic digestion, preventing the waste in the first place saves nine times more compared to anaerobic digestion (4).

Feed Conversion Ratio (FCR) is a metric commonly used to measure the efficiency, and hence sustainability, of an animal product such as meat. It refers to the ratio of feed required to produce a set amount of product; this is typically represented as the amount of protein fed required to produce a kilogram of protein as a food product, whether beef/milk/eggs etc. Typical calculations generally class farmed fish such as salmon having the lowest (i.e. best) FCR, with grass fed meat such as beef or lamb typically ranking as the least efficient, and therefore the least sustainable. 

However, determining the sustainability of a food product by a single metric does not reflect the complexity of our food system. A 100% grass fed steer, raised for 30 months in a conservation grazing system in the uplands would consume no human edible feed and likely be grazed on an area that could not be used to grow human edible food, require no inputs, and contribute to habitat creation and biodiversity value over the course of his life; but due to his relatively longer lifespan and the fact that he will have eaten more forage to get to killweight (and emitted more methane) than his intensive peers, this system is considered inefficient. 

(Photo: Global Farm Metric by the Sustainable Food Trust)

In a 2011 paper (5), Wilkinson suggested that FCR can be too broad a measure, and suggested that we differentiate based on the proportion of an animal’s diet that is made of human edible feed, versus that which is a by- or waste product. According to these metrics, grass finished spring-calving upland suckler beef and lowland lamb are the most efficient systems of meat production, as they consume no human-edible protein, unlike poultry and pig systems which require high-protein feeds (6). Given that over 50% of cereals grown in the UK are destined to become livestock feed, it’s important to consider the indirect land use and food security implications of more efficient/intensive systems; these arable areas could be used to grow crops for humans, or at least for monogastric animals such as pigs and poultry which cannot be reared on pasture alone, like ruminants (7)

This isn’t to suggest that Sainsbury’s perspective is inherently wrong, but we should consider what potential benefits we lose out on by viewing the only positive output from a livestock system as the food we directly eat. As an example, cattle and sheep can be grazed in arable and horticultural rotations to reduce pest and disease burden, while cycling fertility without the need for synthetic fertilisers, all while producing a high value food product, meat (8). In these cases, not only are you producing a secondary “crop” of livestock from an area, but their presence can increase the yield and reduce costs of the primary field crop as well. Grazed carefully, livestock can improve soil health making land more resilient to drought and flooding, which is crucial for food security in our rapidly warming climate. If we integrate trees into these systems, as in agroforestry, we see further benefits according to a whole range of metrics including carbon sequestration, animal welfare, biodiversity, indirect yield (through tree crops) and direct yield (by improving the microclimate for the crop in question and supporting beneficial insects and bird species). 

(Photo: PfL certified Court Farm, Kent)

This is simply in terms of pure production practices; other considerations could include water usage, cultural and heritage value, labour and exploitation, community benefits, biodiversity impact, nutritional value, resilience (whether to extreme weather, pest and disease, supply chain disruption etc) soil health, circularity, animal welfare, food access and equity, and more.

Single metrics are a useful tool in understanding the intricacies and impacts associated with a specific aspect of the food system; the risk lies when they are viewed instead as a silver-bullet by those looking for a solution. What happens in these cases is we lose sight of the complexity of the overall picture. Agriculture, and the food system more generally, is like a vast spider’s web, and tugging at one strand sets off a stream of consequences, both anticipated and not, beneficial or otherwise. 

Simply substituting our current paradigm which values productivity, for a “green” paradigm which values “efficiency” (or a specific interpretation of it) is not going to lead to the change required to make a truly sustainable and future-proof food system. The problems and challenges at the heart of our food system are complex, so our solutions, including how we measure them, must reflect that. 


1, Our reduced carbon beef: Beef that’s better for the planet.

2, “An Industry Leading Integrated Beef Supply Chain From.” ABP Gamechanger.

3, Julian Cottee, Caitlin McCormack, Ella Hearne, Richard Sheane. “The Future of Feed: How low opportunity cost livestock feed could support a more regenerative UK food system” WWF 2022

4, Feedback, “Bad Energy: Defining the true role of biogas in a net zero future”  (2020) London.

5, Wilkinson, J.M. “Re-Defining Efficiency of Feed Use by Livestock.” Animal 5, no. 7 (2011): 1014–22.

6, (It is worth noting that pigs could compare more favourably if they were allowed to be fed food waste, but current regulations in the UK prohibit this, and food waste itself is not without environmental impact; see Footnote 6.)

7,  Clearly there are various boundaries that would need to be enforced to avoid leading to perverse outcomes, such as further land use change as a result of extensifying intensive cattle systems (greater integration of ruminants into arable and horticultural systems can also reduce this risk), utilising land gains for non-food crops such as biofuels, and outsourcing our meat production to other countries.

8, “The Benefits of Sheep in Arable Rotations – National Sheep.” National Sheep Association

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