Did European pig-welfare legislation reduce pig welfare? Perhaps not, but experts confirm that common indestructible materials are not proper enrichment for pigs at all, except perhaps for an enhanced novel branched-chains design.


Published as:
Marc B.M. Bracke and Paul Koene, 2019. Expert opinion on metal chains and other indestructible objects as proper enrichment for intensively-farmed pigs. PLOS ONE. Available at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0212610.

EC Directive 2001/93 requires that all pigs have access to proper investigation and manipulation materials. Intensively farmed pigs in Europe are frequently provided with a short/bare metal chain with or without an indestructible object attached to the chain. To date authorities are regarding this as proper enrichment. However, it has become increasingly clear that the chains do not provide proper enrichment, and that adding an indestructible object such as a ball, pipe or hard wood to the end of the chain may even reduce pig welfare. To test this hypothesis an expert survey was conducted. In total 36 international experts, mostly pig-welfare scientists, responded to the survey.

The experts only marginally agreed with the hypothesis (agreement score 4.6 on average on a scale from 0-10). However, indestructible materials generally received very low scores for welfare, indicating they did not provide proper enrichment. Ranked from low to high average welfare score, the objects were grouped in 5 significance levels:

Level 5 (totally insufficient): Chain hanging too high (for most of the smallest pigs in the pen; average score 1.3 on a scale from 0 to 10 where 5.5 would be ‘acceptable’)

Level 4 (extremely insufficient): Short chain (3.1), Small ball (2.8) and Big ball (average 2.5)

Level 3: (very insufficient) Pipe (3.5) and Bare chain (3.3)

Level 2-3 (very/rather insufficient): Hard wood (3.7)

Level 2 (rather insufficient): Chain on the floor (average: 4.4)

Level 1 (almost sufficient): Branched chains (5.1)

Compared to the marginal enrichment provided before the EC Directive 2001/93 was implemented in 2007 (in the Netherlands generally a short/bare chain, scoring 3.1 and 3.3 respectively, i.e. Level 3-4), adding balls or pipe , as commonly done in The Netherlands and Germany, does not improve pig welfare. Hard wood, as practised esp. in the UK, is a most marginal improvement (only 0.4 higher on average than Bare chain). Chain on the floor scored a bit better (4.4), without being acceptable (set at 5.5). The ‘new’ Branched chains scored significantly better than all other indestructible materials and its welfare score (5.1 on average) was close to the pre-defined level of acceptability (5.5 on a scale from 0, worst, to 10, best). The welfare benefits of adding balls, pipes or hard wood to the metal chain were marginal, and well below what the experts considered acceptable enrichment. The branched-chains design, by contrast, appears to be the most viable alternative. It involves providing a longer chain, i.e. with the free end reaching to floor level, adding ‘branches’, i.e. several short chains ending at the nose height of the pigs, and providing more chains per pen (i.e. 1 branched chain per 5 pigs). Therefore, the implementation of current pig-enrichment legislation needs revision. Branched chains should be implemented widely (across the globe) and in the short term as a first step towards, and benchmark for, providing proper enrichment to intensively-farmed pigs.

The above summary of the publication is a personal version of the first author. See also the related publication and posts on the FareWellDock website:

Chains as enrichment for pigs (Book chapter with supplement)
Pig animation – Improved, branched chain design as proper enrichment for pigs
Branched chains as enrichment for pigs (technical description, pictures and video)
Proper enrichment for intensively-farmed pigs – From review to preview
A collection of pictures of other enrichment materials for pigs can be found here: Prize contest (Prijsvraag) 2011.
Do pigs play with chains? Science versus society

Original abstract of the PLOS ONE paper:

Marc B.M. Bracke and Paul Koene, 2019. Expert opinion on metal chains and other indestructible objects as proper enrichment for intensively-farmed pigs. PLOS ONE. Available at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0212610.

Abstract

EC Directive 2001/93 requires that all pigs have access to proper investigation and manipulation materials. Intensively farmed pigs in Europe are frequently provided with a short metal chain with or without an indestructible object attached to the chain. To date authorities are regarding this as proper enrichment, perhaps with (in)direct reference to the RICHPIG model as a justification. However, it has become increasingly clear that the chains do not provide proper enrichment, and that adding an indestructible object to the end of the chain may even reduce rather than improve pig welfare. To test this hypothesis an expert survey was conducted containing 26 more or less compound questions. On a scale from 0 to 10 experts specified their level of agreement with the hypothesis, the prevalence and welfare scores of nine indestructible enrichment materials. In total 36 experts, mostly pig-welfare scientists, responded (response rate: 39%). Indestructible objects are less prevalent in countries that provide straw (like Sweden and the UK) and outside the EU (US). They are more prevalent in the Netherlands, Belgium, France and Finland, while the prevalence seems to be low in Spain. Balls, wood and pipes were provided most frequently: hard wood especially in the UK (as specified in farm assurance); indestructible balls and pipes in Germany and the Netherlands. The experts’ score for agreement with the hypothesis was only 4.6 on average (scale 0-10; n=25). Enrichment materials, ranked from high to low welfare score, were grouped in 5 significance levels as indicated by different superscripts based on Wilcoxon signed rank tests: Branched chains (5.1a), Chain on the floor (4.4b), Hard wood (3.7bc), Pipe (3.5c), Bare chain (3.3c), Short chain (3.1d), Small ball (2.8d), Big ball (2.5d), and Chain hanging too high (1.3e). Branched chains scored significantly better than all other indestructible materials and its welfare score (5.1 on average) was close to the pre-defined level of acceptability (5.5 on a scale from 0, worst, to 10, best). The welfare benefits of adding balls, pipes or hard wood to the metal chain were marginal, and well below what the experts considered acceptable enrichment. The branched-chains design, by contrast, appears to be the most viable alternative. It involves providing a longer chain, i.e. with the free end reaching to floor level, adding ‘branches’, i.e. several short chains ending at the nose height of the pigs, and providing more chains per pen (i.e. 1 branched chain per 5 pigs). Branched chains should be implemented widely and in the short term as a first step towards, and benchmark for, providing proper enrichment to intensively-farmed pigs.


Branched chain
Two organic pigs interacting simultaneously with a branched chain in the snow. Despite access to a straw bed for rooting, even organic pigs may interact with such chains for long periods of time, esp. directed towards the floor. In fact they will root the chain on the floor more than twice as much as playing with it in a horizontal position. In intensive pig production chains are often (too) short, and when a hockey-type ball or ‘sustainable’ plastic pipe is attached to the end of such a chain the pigs’ interest, and their welfare, is often even reduced further.
Two pigs playing simultaneously with a preferred anchor-type branched chain design.



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