Of the enrichment objects tested in the research project, the best turned out to be those made of fresh wood. The wood was collected from forest during the previous two to three months. Fresh wood has more odour than board or other older wood, and the material is slightly more pliable, making it better for chewing. Birch was the favourite tree species, but other non-conifer species work too.
The recommended thicknesses and lengths of the pieces are as follows:
Weaned piglets 4–7 cm 20–50 cm
Finishing pigs 5–10 cm 40–100 cm
Breeder pigs approx. 10 cm 40–100 cm
The recommended quantity is at least 20–25 cm per each slaughter pig or breeder pig. For weaned piglets, only one quantity was tested in this research project, so there is not sufficient results to base exact recommendations on. As a rough estimate, 10 cm per weaned piglet can be recommended as a minimum.
The attractiveness of the wooden pieces to pigs depends greatly on how the pieces are attached in the pen. Several options were tested in the research project. The worst arrangement - the one that turned out to be the least interesting to pigs - was a metal rack attached on the pen wall, into which a length of wood was inserted in a vertical position, with only part of the wood exposed to the pigs. The best solution turned out to be the following:
The pieces of wood are suspended from the pen wall on metal chains, so that the pieces wood are in a horizontal position above the floor level but below snout level. In pens with only partly slatted floors, it is recommended to attach the wooden pieces above the solid floor. Suspending the pieces at a little distance from the pen wall, for example by attaching one chain in the front corner of a straw rack and the other end on the pen wall, will somewhat reduce the wear on the pen wall.
The recommended type of chain for suspending is hot-dip galvanized, long-link chain, with a diameter of 3 mm for weaned piglets and 4 mm for finishing pigs and breeder pigs. They are attached to the wooden pieces with bolts, locking nuts i.e. elastic stop nuts (as ordinary nuts can come loose when the pigs manipulate the objects) and washer rings that prevent the bolt and nut from slipping through a chain lenk. Nuts and bolts of 5 mm will fit a 3 mm chain; nuts and bolts of 6 mm, a 4 mm chain.
Before the next arrival of the next batch of pigs, the wooden pieces and chains are washed with a pressure washer, as is the rest of the pen. If the sizes and quantities of the wooden pieces are as above, they will last for a few years before wearing off. However, pigs seem to start losing interest in them after half a year, possibly because the odour has changed from fresh wood to pig-farm smell. For this reason, and also for hygiene, it is recommended to remove the wooden pieces twice a year and attach new ones on the chains.
Shorter lengths of wood can be suspended on one chain. The chain is recommended to be a bit shorter in this case, so that the wooden piece is approximately at snout height. This prevents the chain from getting wrapped around the neck of a pig. Another safe solution is to attach two pieces of wood on each single chain, as in the photo above: one piece at snout height and another near the floor level.
How to attach chains on the pieces of wood: Drill a hole through the middle of the wood, thread the chain through it and attach with a lock nut, bolt and washer rings. Attach the upper end of the chain on the pen wall.