Trade-offs in the externalities of pig production are not inevitable

Farming externalities are believed to co-vary negatively, yet trade-offs have rarely been quantified systematically. Here we present data from UK and Brazilian pig production systems representative of most commercial systems across the world ranging from ‘intensive’ indoor systems through to extensive free range, Organic and woodland systems to explore co-variation among four major externality costs. We found that no specific farming type was consistently associated with good performance across all domains. Generally, systems with low land use have low greenhouse gas emissions but high antimicrobial use and poor animal welfare, and vice versa. Some individual systems performed well in all domains but were not exclusive to any particular type of farming system. Our findings suggest that trade-offs may be avoidable if mitigation focuses on lowering impacts within system types rather than simply changing types of farming.


Tradeoffs in the externalities of pork production are not inevitable: Supplementary Materials
Figure 1 Land-use cost and GHG cost of 74 breed-to-finish UK pig systems.GHG costs here included animal source emissions, those associated with feed production, transport, energy use, slaughter and processing, but excluded foregone sequestration.rs and p values are from two-sided Spearman rank correlations on a subset of our data (n=43) with one datapoint selected randomly from those that shared breeding and/or rearing herds (see Methods).(n=8) with one datapoint selected randomly from those that shared breeding and/or rearing herds.Our sample was too small to identify significant differences among husbandry types.

RSPCA assured
Farrowing can be indoors, but sows must be allowed to turn around at all times.
Pigs must have access to unperforated floors and sufficient bedding.
12 (of which 10 are also Red tractor) unknown 222,000 (unknown)

Free range
Always outdoors.

Woodland
Pigs are kept at least with partial tree cover, but farms could also include some indoor housing.
3 (of which 2 are also free range) unknown 13,000 (unknown)

Organic
Always outdoors.

(of which 5 are also
Red tractor, RSPCA assured and all 6 are free range) 0.6 31,000 (47%) Table 3 Description of the 17 breed-to-finish pig systems studied in Brazil, by husbandry type as there are no established labels.

Hybrid indoor-outdoor
Typically indoors.Fully slatted floors are permitted.GHG cost (x axis) included emissions from animals, energy, fuel, transport, feed production, manure management and foregone sequestration (see Methods).GHG cost: half sequestration rates (y axis) assumed that the forgone sequestration rates were half those in GHG cost.rs and p values are from two-sided Spearman rank correlations on a subset of our data (n=43) with one datapoint selected randomly from those that shared breeding and/or rearing herds (see Methods).

Supplementary Methods
The following sections outline the equations used to calculate externality costs, which were all calculated over the most recent year of available data.

Land-use cost
Land-use cost was calculated using Equation 1: where u refers to each farm making up a system; La refers to the annual m 2 required to rear the pigs, which is the area paddocked and/or housed, excluding any land under tree cover.
Lf and refers to the land required to grow feed, calculated using farm-and production stagespecific feed formulations, and quantities used of each.DW refers to the kg of DW produced and includes DW from finishing pigs and sows sent to slaughter, equated using economic allocation.See Methods for further explanation of method choices and data sources.
where i refers to the WQ principles of Good health, Good feeding, Appropriate behaviour and Good housing; p is the WQ principle score, with 0 being the worst possible score and 100 being the best; w is the weighting applied to each principle score; y is the quantity of life years needed to produce 1kg of DW, SP refers to sows and piglets and FP to fattening pigs.T is the WQ principle score at which a welfare cost transitions to be being a welfare benefitwhere quality of life is high enough that more life-years experiencing it is deemed a benefit to animal welfare.Both w and T are challenging to quantify, but the ranking of farms and farm types was found to be largely insensitive to the choice of both 3 .Therefore, we took intermediate approaches to both: w was 0.35, 0.25, 0.25 and 0.15 for Good health, Good feeding, Appropriate behaviour and Good housing respectively; and T was 80.

Figure 2
Figure 2 Land-use cost and GHG cost excluding foregone sequestration for 17 Brazilian pig systems.rsand p values are from two-sided Spearman rank correlations on a subset of our data (n=8) with one datapoint selected randomly from those that shared breeding and/or rearing herds (see Methods).

Figure 3
Figure 3 Externality costs of 17 Brazilian pig systems, with two systems with poorer quality data removed.rs and p values are from two-sided Spearman rank correlations on a subset of our data

Figure 4
Figure4Sensitivity of GHG cost to accounting for avoided emissions due to manure replacing fertiliser on our 74 UK datapoints.GHG cost (x axis) included emissions from animals, energy, fuel, transport, feed production and manure management.This assumed that nitrogen remaining in manure was spread on fields and displaces fertiliser use as in ref.1 .GHG cost excluding avoided emissions (y axis) assumed manure did not displace any fertiliser use.rs and p values are from twosided Spearman rank correlations on a subset of our data (n=43) with one datapoint selected randomly from those that shared breeding and/or rearing herds (see Methods).

Figure 5
Figure 5 Sensitivity of GHG cost to accounting for forgone sequestration, for our 74 UK datapoints.

Table 1
UK breed-to-finish pig systems in the top performing 50% for three externality costs

Table 2
Description of the 74 breed-to-finish pig systems studied in the UK.The label categories are approximately ordered by the degree of standards required by each, with more demanding categories exceeding the standards of lower categories.From least to most demanding the categories are no assurance or labelling ("None"), Red tractor (including Quality Meat Scotland; QMS), RSPCA assured, free range, woodland and Organic.If systems met the requirements for multiple labels, they were included in the most demanding label typefor example, free range systems that are also RSPCA assured are included in the free range category.Relevant label standards or guidelines can be found at the following websites: Red tractor (www.redtractorassurance.org.uk),QMS (https://qmscotland.co.uk),RSPCA assured (https://science.rspca.org.uk/sciencegroup/farmanimals/standards/pigs) and Organic (www.soilassociation.org/organicstandardsand www.orgfoodfed.com).The fifth column shows the percentage of the total slaughtered fattening pigs in the UK in 2021 (from www.gov.uk/government/statistics/cattle-sheep-and-pig-slaughter) that is accounted for by each label type (according to www.pig-world.co.uk/news/highlighting-the-differences-how-uk-welfare-standardscompare-with-our-competitors).These sum to more than 100% as systems often have multiple label types.The final column shows the annual slaughtered fattening pigs from our 74 systems, summed by label type and rounded to the nearest 1,000, and our estimate of the % of all slaughtered pigs belonging to that label type which they represent.In total, our study covers ~5% of UK slaughtered fattening pigs.