Since the 1980s, the Danish pig industry has focused on untethered sows. The ongoing development of new pig house systems is an important part of this. Since 1998, it has been a requirement under Danish law for sows being untethered in the gestation units. In 2013, also EU legislation to this effect was passed.

Since the end of the 1980s, the Danish pig industry has been involved in the development of a pig house system for untethered sows. At first, the focus was on untethered gestating sows since Danish law to this effect was not passed until 1 January 1998 requiring for sows to be untethered in all new gestation units, and then from 2 January 2013, EU law required untethered sows in all gestation units in the EU.

In 2014, another Danish special law was passed requiring for untethered sows in the heat unit where the sows are being fertilised to be placed in new pig houses built after 1 January 2015 and in all pig houses from 2035. In relation to untethered sows in pig houses where sows give birth, the industry's own target is that 10 per cent of the sows must be untethered during the suckling period by 2020.