Pigs have strong exploratory drives that are entirely thwarted in barren concrete environments, with the absence of novel stimuli and manipulable objects causing chronic boredom that reduces welfare and increases aggression.
Pig curiosity is not a pleasant extra — it is an expression of a cognitive drive that, when thwarted, creates negative affective states that compound across the production period. Pigs that cannot explore, manipulate, and investigate their environment are in a state of chronic understimulation that is welfare-relevant in proportion to their cognitive capacity. The ease of addressing this — with inexpensive manipulable objects and straw — makes the continued provision of barren pig housing an ethically unjustifiable welfare failure.