Stocking density affects welfare indicators of growing pigs of different group sizes after regrouping

In recent years, the concept of animal welfare began to be accepted by the Chinese people. On some intensive pig farms, the stocking density for growing pigs is too great, leading to decreased animal welfare. In order to study the relationships between stocking density and welfare indicators and determine the optimal stocking density for growing pigs, a total of 243 Landrace x Large White cross barrows were randomly regrouped at 1.6 m(2), 1.2 m(2) or 0.8 m(2) per pig at 135 days of age. Behavior percentages, lesions on the body and tail, body surface temperature (BST), manure on the body and concentrations of salivary cortisol were measured during the first 15 days after regrouping. Pigs housed at 0.8 m(2) per animal spent more time drinking (1.89 vs. 1.01%, P=0.0048) and participating in negative social behavior (0.76 vs. 0.26%, P=0.0063) than those housed at 1.6 m(2) per pig. Pigs housed at 1.2 m(2) per animal showed more positive social behaviors (1.28 vs. 0.14%, P=0.04) than those housed at 1.6 m(2). Pigs housed at 0.8 m(2) per animal had more lesions on the ears (P<0.01), front (P<0.01), middle (P<0.01) and hind-quarters (P<0.01) regions than those housed at 1.6 and 1.2 m(2). Total scores of lesions on the body were gradually increased (P<0.01) with the increasing stocking density. Pigs housed at 0.8 m(2) per animal had more manure on their bodies than pigs at 1.6 and 1.2 m(2) at the 7th, 11th, 13th and 15th day after regrouping. Pigs housed at 0.8 m(2) per animal had a greater proportion of pigs with an abnormally high BST than those at 1.6 (10 vs. 1.9%, P=0.009) and 1.2 (10 vs. 4%, P=0.037) m(2) per pig. Altogether, at the first 15 days after regrouping, pigs housed at 1.2 m(2) per animal had decreased housing costs compared to those housed at 1.6 m(2) and improved indicators of animal welfare compared to those housed at 0.8 m(2). (C) 2015 Elsevier B.V. All rights reserved.