Crowding of grow-finish pigs reduces growth and is considered a welfare issue. Most crowding studies have been limited to smaller group sizes than are currently being considered in the swine industry. It has been hypothesized that pigs in large groups require less space to maintain growth and welfare. The objective of this study was to examine the effects of group size and space allowance on the performance, health and welfare of grow-finish pigs. The study consisted of eight blocks, each with four experimental units in a 2 x 2 factorial arrangement of group size (18 vs. 108 pigs/pen) and space allowance (0.52 vs. 0.78 m2/pig). Health assessments were conducted daily; production data were collected weekly; injury scores, behaviour and salivary cortisol data were collected bi-weekly; and carcass and adrenal gland data were collected at slaughter. Gains were lower for crowded pigs, but the effects were limited to the final week of the study. Pigs in crowded groups had a lower feed efficiency, which followed a trend similar to that of gains over time. In the crowded groups, pigs spent less time at the feeder, but no other variables differed among space allowances. Gains were lower for pigs housed in large groups, but the effects were limited to the initial two weeks of the study. Pigs in large groups had a lower feed efficiency and more lameness and leg sores. Other health measures did not differ between the group sizes. Lying behaviour of pigs in large groups indicated that they were able to utilize free space more efficiently than pigs housed in small groups. Analysis of feeding patterns suggests that pigs housed in large crowded groups were able to manoeuvre around their environment more easily than those in small crowded groups, yet performance of pigs in large groups was similarly affected by space restriction as pigs in small groups. Interactions of group size and space allowance indicated that pigs in large crowded groups were more susceptible to lameness. There was no indication that pigs in large groups required less space, or could perform as well at reduced space allowances, than pigs in small groups.

Crowding of grow-finish pigs reduces growth and is considered a welfare issue. Most crowding studies have been limited to smaller group sizes than are currently being considered in the swine industry. It has been hypothesized that pigs in large groups require less space to maintain growth and welfare. The objective of this study was to examine the effects of group size and space allowance on the performance, health and welfare of grow-finish pigs. The study consisted of eight blocks, each with four experimental units in a 2 x 2 factorial arrangement of group size (18 vs. 108 pigs/pen) and space allowance (0.52 vs. 0.78 m2/pig). Health assessments were conducted daily; production data were collected weekly; injury scores, behaviour and salivary cortisol data were collected bi-weekly; and carcass and adrenal gland data were collected at slaughter. Gains were lower for crowded pigs, but the effects were limited to the final week of the study. Pigs in crowded groups had a lower feed efficiency, which followed a trend similar to that of gains over time. In the crowded groups, pigs spent less time at the feeder, but no other variables differed among space allowances. Gains were lower for pigs housed in large groups, but the effects were limited to the initial two weeks of the study. Pigs in large groups had a lower feed efficiency and more lameness and leg sores. Other health measures did not differ between the group sizes. Lying behaviour of pigs in large groups indicated that they were able to utilize free space more efficiently than pigs housed in small groups. Analysis of feeding patterns suggests that pigs housed in large crowded groups were able to manoeuvre around their environment more easily than those in small crowded groups, yet performance of pigs in large groups was similarly affected by space restriction as pigs in small groups. Interactions of group size and space allowance indicated that pigs in large crowded groups were more susceptible to lameness. There was no indication that pigs in large groups required less space, or could perform as well at reduced space allowances, than pigs in small groups.