Livestock Production/Industries, alternative housing systems, animal welfare, economic optimisation, farrowing systems, pig,

Baxter, Emma

Edwards, Sandra

Lawrence, Alistair

Stott, Alistair W.

Vosough Ahmadi, Bouda

English

Research Papers in Economics

LAND ECONOMY WORKING PAPER SERIES
___________________________________________________________________
Number 36: Animal welfare and economic optimisation of 
farrowing systems
Corresponding Author:
Bouda Vosough Ahmadi
Land Economy Research Group
SAC Research Division
SAC Edinburgh
EH9 3JG
Tel: 0131-535-4216
Email: bouda.v.ahmadi@sac.ac.uk2
ANIMAL WELFARE AND ECONOMIC OPTIMISATION OF FARROWING SYSTEMS
Bouda Vosough Ahmadi
a, Emma Baxter
b, Alistair Stott
a, Alistair Lawrence
b and Sandra Edwards
c.
ABSTRACT 
Currently, farrowing crates dominate indoor pig farrowing in the UK (~ 60% of herds). Such systems raise 
welfare problems due to close confinement of the sow. Although, many alternative housing systems have been 
developed in different countries, no commercially viable/feasible option has emerged for large-scale units. 
We have reviewed current scientific and practical knowledge of farrowing systems to identify alternative 
systems, their welfare and production potential. Our aim is to establish acceptable trade-offs between profit 
and welfare within alternative farrowing systems using linear programming, hence designing high welfare 
but commercially viable alternatives to the farrowing crate. System-specific results of interactions between 
welfare components and financial performances have been analysed and presented in this paper.
. 
KEY WORDS: alternative housing systems, animal welfare, economic optimisation, farrowing systems, pig
                                                
a Land Economy and Environment Research Group,Scottish Agricultural College
b Animal Behaviour and Welfare, Scottish Agricultural College
c School of Agriculture Food and Rural Development, Newcastle University3
INTRODUCTION
In 2006, around 73% of the 477,000 breeding sows in the UK farrowed in crates (Defra, 2007) raising welfare 
concerns. Development of an alternative, economical farrowing system that provides high sow and piglet 
welfare is regarded as beneficial for industry and the animals (Johnson and Marchant-Forde, 2009). Although, 
many alternative housing systems have been developed in different countries, no commercially viable/feasible 
indoor option has emerged for large-scale units. The main conflict, yet to be resolved, is between the sows’ 
reproductive performance (profit) and sow/piglet welfare. This conflict is largely an issue of how to provide 
the appropriate level of environmental enrichment to meet the biological requirements of the farrowing sow 
given management and business constraints. Therefore, a study was initiated to: i) identify and investigate 
alternative indoor free farrowing systems which are commercially viable, and ii) to develop and redesign the 
farrowing environment from biological first principles to maximise welfare and production performances of 
piglets  and  sows.  In  this  context,  animal  welfare  scientists,  engineers,  expert  stakeholder  groups  and 
economists  worked  together  to  synthesise  information  to  identify  a  system  prototype  including  potential 
innovations. A linear programming (LP) approach (Barnard and Nix, 1997) was used as a framework to test 
possible  trade-offs  between  profit  and  welfare  within  alternative  indoor  farrowing  systems.  We  studied 
conventional crates, simple pens and designed-pens (i.e. modified with separation of dunging and lying areas 
and addition of pen “furniture”), to explore the possibility of providing higher welfare within the context of 
commercially viable alternatives to farrowing crates. This paper outlines the LP framework used as part of the 
design process, highlighting the main issues arising at the biological/economic interface and first steps taken 
to address them.
MATERIALS AND METHODS
Optimisation model
LP uses technical coefficients to link key activities (e.g. farrowing and lactation) with resources they require 
such  as  feed,  labour,  space,  power  etc.  This  normally  provides  the  physical  input-output  relationships 
determining profitability. The LP then chooses the combination of activities that maximises the objective (net 
margin at age 28 days (i.e. sales of weaners minus attributed fixed and variable costs)) subject to the resource 
constraints applied.  However, in this case the welfare implications of the system chosen also needed to be 
incorporated. Biological needs of the sow and piglets during nest-building, parturition and lactation phases 
were therefore reviewed and three main “welfare components” (WC) namely space, substrate and temperature 
were identified. Baseline WC constraints and coefficients characteristic of each system were included in the 
LP. Activities were introduced (i.e. extra labour, space, power and substrate) to allow WC constraints to be 
relaxed (within limits of a given system) thus improving welfare and possibly productivity (reduced piglet 
mortality) at some additional expense. The LP would then enhance welfare within any system provided that 
the extra WC raised net margin. The cost of additional welfare beyond this point could be estimated using 
sensitivity  analysis.  SAC  (2008)  was  used  as  the  main  source  of  financial/performance  data  for  the 
conventional  crate  system.  Quantitative  values  from  145  items  of  the  reviewed  literature  were  used  to 
populate a database providing required data on the other studied farrowing systems.
LP details
The  LP  was  implemented in  Excel  (Microsoft  Corporation,  2002). As  a  first  attempt  at determining the 
relationships between WC coefficients and total piglet mortality, the related functions were assessed by the 
animal welfare scientists aiming at providing quantitative figures based on available scientific evidence rather 
than expert opinion. Assessing these relationships is, however, limited by the scarcity of relevant underlying 
data,  thus  introducing  a  degree  of  uncertainty  about them  and  the  model’s  outputs.  Besides  coefficients 
representing  WC  and  piglet  mortality  relationships,  input  and  output  variables  were  distinguished.  Input 
variables concern input on technical performance, such as litter size, piglet mortality and weaning rate (i.e. 
piglet to weaner flow). The average number of live piglets born per litter under the three systems studied was 
designated at 11.0. Initial corresponding total piglet mortality rates (including stillbirths), based on a summary 
of published surveys and experimental studies, were 19.8%, 20.6% and 16.54% for crate, pen and designed-
pen respectively. The LP calculated a farm net margin for each system based on the average physical and 
financial assumptions/input data for the relevant set of WC. In parallel to this optimisation practice, a welfare 
score for each system is under development. The preliminary results are presented here.
RESULTS
LP  derived total  space per  pen was  3.6,  11.1 and  7.0m
2 for crates,  pens and  designed-pens respectively 
(Figure 1). The LP utilised a higher amount of substrate in designed-pens than pens and crates. Crates with 4
6.9 and pens with 12.7 hours per sow per year had the lowest and highest labour requirements. Also the crates 
obtained the highest annual net margin (at weaners’ age 28 days) per sow (£418) and the designed-pens and 
the pens with the net margins of £365 and £333 were in the second and third place (Figure 2). Taking account 
of both sow and piglet needs, the designed-pens obtained the highest welfare score of 2.39 whereas crates 
achieved a score of 1.25 which was slightly higher than the pens’ welfare score of 1.03.  These preliminary 
results suggest that, there is around 13% difference in net margin between crates and a designed-pen which 
provides higher welfare than farrowing crates. Further research is required to develop better WC coefficients 
and production performance relationships and to perform sensitivity analysis.
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Figure 1. Total amount of inputs (per sow per year) used by the LP for the three farrowing systems.
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Figure 2. Graphical illustration of the optimised annual net margin/sow (at weaners’ age 28 days) of the three 
studied farrowing systems against their associated welfare scores. 
REFERENCES
Barnard, C. Nix, J., 1979. Farm Planning and Control, 2nd edition. Cambridge University Press, Cambridge.
Defra, 2007. Department for Environment, Food and Rural Affairs Agriculture in the United Kingdom 2007.
Johnson, A.K and Marchant-Forde, J.N., 2009. The welfare of pigs, Animal welfare 7, 141:188. Springer 5
Science + Business Media Publication.
Microsoft Corporation, 2002. Excel 2002 Spreadsheet. Microsoft Corporation, Washington.
SAC, 2008. Farm Management Handbook, vol. 2008/9. SAC, Edinburgh.

Excel

Farm Planning and Control, 2nd edition.

The welfare of pigs,

ANIMAL WELFARE AND ECONOMIC OPTIMISATION OF FARROWING SYSTEMS

ANIMAL WELFARE AND ECONOMIC OPTIMISATION OF FARROWING SYSTEMS

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