The large study, from several institutions, suggested minimal long term impacts on reproduction and welfare from higher cortisol levels and aggression, exhibited by sows immediately after mixing and at reduced floor space.

It investigated how floor spaces between 1.45 and 2.9 square metres affected the welfare and performance of sows grouped within four days of mating.

Study leader Professor Paul Hemsworth, like his colleague Dr Jean-Loup Rault in a previous study, found aggressive interactions and cortisol levels at day two after mixing declined with increasing floor space, but there were no effects at day 26.

Dr Roger Campbell, CEO of the Co-operative Research Centre for High Integrity Australian Pork (Pork CRC), explained that although floor space between 1.45 and 2.9 square metres had no long term effects on sow welfare or reproduction, aggression and cortisol levels were markedly affected by floor space immediately after mixing.

“However, sows change their behaviour rapidly and these effects disappeared by day 26 and a corollary study showed the effects had actually disappeared by day nine,” he said.

According to Dr Campbell, the bottom line for Australia’s pork producers, the majority of whom (70 per cent based on industry surveys) have moved to group housing, is there probably is no optimum or minimal floor space for group housed sows as they adapt rapidly to mixing and to reduced floor space.

“Pork CRC results show aggression and cortisol levels immediately after mixing can be reduced by increased space.

"This supports the mixing pen concept where sows are given more space in the week after grouping and then their space allowance can be reduced.

“Aggression at mixing and immediately after can’t be eliminated, and Pork CRC participant feedback is floor space of 1.8 to 2 square metres supports good performance,” he said.

Further Reading

Read a report on the project and a full author list here.