Metal chain is quite commonly used as enrichment on pig farms, because it is durable and lasts for a long time. However, in this research project it turned out to be the the least useful among all the materials tested.
The research results showed that pens with metal chains as the only enrichment objects had more tail biting and ear biting than pens with enrichment objects made of fresh wood. Additionaly, pigs used chains significantly less than wooden or plastic objects. Providing a supposedly more interesting chain with several branches in it did not make it more attractive than an ordinary chain, nor was there any improvement in tail and ear biting.
One of the reasons for the inefficiency of metal chain is that there are not many activities a pig can do with it. For instance, it is not possible to actually chew on a chain, but instead pigs just move it around in their mouths.