How Housing Conditions Determine the Welfare of Pigs

Simple Summary The increasing interest in the welfare of farmed animals has resulted in the development of alternative production systems for pigs. Access to outdoor pens or pastures is considered to improve welfare, as it is environmental-friendly and widely accepted by society. Outdoor housing allows pigs to freely display their natural behaviors, which is perhaps the most significant advantage of this type of housing vs. indoor housing systems. Among various indoor systems, bedding made of different materials, especially straw, appears to promote appropriate behavioral patterns in pigs, but it may also lead to respiratory disorders. However, the literature indicates that none of the described housing systems for pigs is perfect, and each one has some negative effects on welfare, management, and food safety. Humans who care for pigs prefer an environment that not only allows the pigs to express their natural behaviors but also limits the development of aggression and stereotypes. Most of the behavioral and health problems encountered by pigs in barren, conventional conditions are solved by alternative housing systems. However, it is not known whether these systems are advantageous in terms of the performance of pigs. In this work, we review the effects of housing systems on pigs' behaviors and performance, which are among the major indicators of the welfare of these animals. Research results point out that outdoor systems are more ideal for sows and fatteners than buildings. Nonetheless, outdoor housing is associated with two major effects in both groups: increased activity due to environmental exploration and higher space allowance, and increased incidence of injuries compared to indoor systems. Sows are more active when housed in groups, but they experience an increased frequency of injuries. According to the literature, group-housed sows give birth to healthy piglets with good daily weight gains. The difference in the fattening and slaughter performance of pigs raised indoors vs. outdoors remains unclear, and the results reported so far are inconsistent. Outdoor systems seem to be associated with a higher incidence of osteochondrosis and lesions of elbow and hock joints, whereas indoor systems cause a greater degree of body soiling in pigs. Based on the reviewed literature, it may be concluded that outdoor housing helps to solve behavioral issues in pigs but leads to other problems in pig production.