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Research results on pig enrichment

The research project "New innovations for environmental enrichment on pig farms"
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Straw Fresh wood Sisal rope Plastic tube Metal chain Other materials

Research on enrichment

A research project called "New innovations for environmental enrichment on pig farms" was carried out in Finland on three commercial pig farms during the years 2012 and 2013. The number of animals in the research project totalled 1436 finishing pigs, 167 breeder pigs and 304 suckling piglets. The project was planned and implemented by the Faculty of Veterinary Medicine of the University of Helsinki. The leader of the project was Professor Anna Valros, and researcher Helena Telkänranta was in charge of planning and implementing the project. Additionally, the planning phase included input by foreign experts such as Marc Bracke of the Wageningen University in the Netherlands and Jeremy Marchant-Forde of the Agricultural Research Service of the United States Department of Agriculture. In the implementation phase, there also were students of animal husbandry and veterinary medicine doing their Masters and Licenciate theses in the project. The project was funded by the Ministry of Agriculture and Forestry in Finland and by the University of Helsinki. The project also collaborated with the Finnish pig producers' association Suomen Sikayrittäjät, which assisted in e.g. recruiting the farms on which the research was carried out.


Research continues


The new international research project FareWellDock is developing further ways to prevent tail biting.

Main results

In finishing pigs, the most successful enrichment objects were pieces of tree trunk with a diameter of 5 to 10 cm, felled rather recently, sawn to lengths of 40 to 100 cm, and suspended on chains in a horizontal position below snout level. Pens with this type of enrichment had a lower level of tail and ear biting as compared to pens with other tested enrichment materials or with the ordinary enrichment of that farm. Pens with fresh wood also had a lower frequency of chewing and biting directed at other pigs, as well as indications of a lower stress level.

Objects made of pipes of polyethene plastic were used as actively as wooden objects, but they did not have the same reducing effect on tail and ear biting, nor on indicators of stress.

In farrowing pens, prividing piglets with suspended sisal ropes lowered the stress level of sows, possibly because the piglets directed some of their biting and chewing activities at the ropes and not at the sow. Ropes on the solid resting area of piglets also reduced the frequency of biting and rooting at other piglets while settling to sleep, but the difference to ordinary farrowing pens was small.

What was tested?

In the first phase of the project, so-called pilot phase, seven materials were tested in various designs. For weaned piglets, finishing pigs and breeder pigs, the materials were freshly cut wood, sisal rope, peat plate, medium density polyethene pipe or PE-MD pipe (previously called PEM pipe; this is the plastic pipe used as water pipe in buildings), feeder chain of metal and ordinary metal chain. For suckling piglets, the materials included sisal rope, toilet paper and peat plate.

The materials were tested in various quantities, built into various types of objects, in various locations in the pen and with various methods of attaching. For fresh wood, the extent of gnawing at four different tree species was compared: aspen, alder, birch and pine. 

The most promising materials and ways of using them were selected to be tested in the main part of the research project. The criteria for selection included safety to pigs and personnel, as well as the cost-benefit ratio. Costs that were taken into account included both material and labour costs. Benefits were assessed by measuring how actively pigs used the objects after having had them for two weeks, when the effect of novelty has worn off. The cost-benefit assessment therefore meant that a material was selected to be tested only if it had small material and labour costs as compared to the increase of being able to fulfil pigs' species-specific behavioural needs.

The objects selected for the main phase of testing were as follows:

For weaned piglets, finishing pigs and breeder pigs:

  • Pieces of recently cut trunks of young birch trees, suspended on metal chains in a horizontal position near the floor level.

  • Objects constructed from pieces of polyethene plastic tube and metal chain.

  • Two metal chains attached together as an asymmetrical cross, forming a chain with three hanging branches of different lengths when suspended from the forth end.

For suckling piglets

  • Sisal ropes suspended on the pen wall, on the solid resting area and as above the slatted area.

In each of the experiments, the objects were attached in the pens before the pigs arrived, and the objects remained in the pens for as long a time as the pigs.

The selected  object types were tested in four  experiments: two experiments on finishing pigs, one on breeder pigs and one on suckling piglets.



How to read the graphs on this page

"Control" refers to the ordinary enrichment on each farm. These types of enrichment were present in all pens, but control pens did not have any other enrichment besides these.

  • Finishing pigs: a straw rack with straw, and a metal chain
  • Breeder pigs: a small quantity of straw once a day and a small quantity of dry feed on the solid floor once a day. Additonally the following, which were in control pens only: a piece of board approx. 30 cm, and a piece of feeder chain of metal, approx. 50 cm
  • Suckling piglets: a small quantity of wood shavings twice a day, and a piece of lightweigth metal chain
In the graphs, the letters a, b and c refer to statistical significance, in other words whether the results can be due to chance. If two columns have different letters above them, the difference between them is reliable with a probablility of more than 95 per cent. If two columns have the same letter, there has been so much variation within the observations summed up n each column that there is more than 5 per cent chance of the difference between columns to be due to chance.

Use of enrichment objects

Enrichment use was the most active in those pens that had objects made of wood or plastic. If birch wood, polyethene plastic pipes and branching metal chains were accessible at the same time, wood was used significantly more frequently than chain, and the activity elicited by plastic was intermediate between these. As for metal chain, there was no difference in the activity of use when an ordinary simple chain was compared to a combination of two chains in a branching design.



Chewing at other pigs

Pigs chewed on and rooted at each other less frequently in those pens that had objects of fresh wood, as compared to pens with plastic tube, metal chain, feeder chain or a single piece of old board.



Fear of strangers

When an unfamiliar person stepped into the pen, pigs in pens with wooden enrichment objects were less fearful than those with other objects. This was measured by how many seconds it took for them to approach before touching the stranger. The result suggests a lower level of stress in pens with wooden objects.

Latency to approach an unfamiliar human, in seconds. The longer times taken to dare approach a stranger suggest a higher level of stress (finishing pigs, experiment 2):



Resting areas and cleanliness of floor

In this research project, the wooden pieces and sisal ropes had been attached in the solid floor area, and the plastic objects and metal chains were on the slatted floor. With this arrangement, the pens remained as clean as those pens wihtout additional objects. The pigs also used the same floor areas for resting.

Tail and ear biting

The prevalence of tail and ear biting was lower in those pens of finishing pigs that had 30 cm of birch trunk per pig, as compared to those pens that had plastic tubes or metal chain.

On another farm, where the use of wood was 10 cm per pig, ear biting was also less prevalent than in other pens. However, in tail biting there was only a tendency for an improvement, not a statistically signifcant difference. 


The abovementioned benefits of wood were approximately the same in those pens where wood was the only added enrichment, and in those where there also was plastic pipes and branching metal chains. In other words, adding other objects besides wooden ones did not further add to the measured benefits.

Behaviour and stress level in farrowing pens

At the age of one week, piglets chewed on and rooted at each other with a lower frequency in pens with sisal ropes on the resting area, as compared to those in pens without ropes. This effect was no longer visible at the age of two weeks.

The results also included the following tendencies. A tendency is a result with a statistical reliability between 90 and 95 per cent. In other words, there has been so much variation between individual pigs in their behaviour or degree of damage that the result has a 5 to 10 per cent risk of having beencaused by chance.

One of the tendencies concerned stress of sows. Tear staining, dark secretion under the eyes indicative of stress, was less intensive in those sows whose piglets had access to ropes. The reason may be that the piglets directed some of their biting and chewing activities at the ropes and not at the sow.  The other tendency was seen in piglets at two weeks of age: before sleeping, piglets moved around for a longer time if they had ropes.