Effects of stocking density and toy provision on production performance, behavior and physiological indexes of finishing pigs

Abstract: Stocking density and toy provision are the major measures widely-used to improve environmental enrichment for pig welfare farming. However, the specific interaction of stocking density and toy provision is still lacking. In this study, a 3×2 arrangement (three stocking density levels × with /without toys) was designed to explore the interaction of stocking density and toys on the production performance, behavior， and physiology indexes of finishing pigs, thereby determining a proper stocking density for the production with/without toy provision in China. A field experiment was conducted in a growing-finishing pig house in Chongqing City from September to November 2018. Stocking density was set at three levels of 0.75, 1.05, and 1.35 m2/pig. A total of 144 finishing pigs with an initial average body weight of 57.0±4.4kg were also randomly assigned into 12 pens with 12 pigs in each pen. Four chewing toys were suspended in each pen for the toy provision group. The results showed that the average daily gain (ADG) of finishing pigs with a 1.35 m2/pig stocking density was 10.0% and 7.7% higher than that of 0.75 m2/pig and 1.05 m2/pig (P<0.05) in the groups without toy settings, whereas, the F/G (feed/gain) was 7.3% and 2.0% lower, respectively (P<0.05). Meanwhile, the average daily feed intake (ADFI) of pigs housed in 1.05 m2/pig was lower than that of two stocking densities (P<0.05). Pigs spent less time on lying and drinking with the increase of stocking density, while more time on feeding and other behaviors when the groups stabilized (P<0.05). There was a significant increase in the surface temperature of the pig body, serum cortisol, and inflammatory cytokines concentrations (P<0.05). Toy provision inside pens enhanced the behavior diversity, while effectively decreased the water consumption and abnormal behaviors (P<0.01), where there was a significant decrease in the serum IgG and inflammatory cytokines concentration (P<0.05). The IL-1β, IL-6 and TNF-α concentrations of pigs housed in 1.05 m2/pig with toy provision at the 53rd day were 20.2% (P<0.01), 23.2% (P<0.05) and 15.7% (P<0.05) higher than those without toys, respectively. Moreover, pigs with toy provision gained more weight and feed intake, especially at lower space allowance environment (0.75 m2/pig). Consequently, a significant correlation was observed in the stocking density and toy provision on water consumption, lying, and feeding behaviors (P<0.05), indicating that the space occupation of toys inside the pen played an essential role to improve the welfare of finishing pigs. A relatively lower stocking density was beneficial to the weight gain, feed conversion, welfare, and health level of finishing pigs. Consequently, toy provision can meet the behavior expression needs of pigs, while greatly reduce the abnormal behaviors and stress levels in barren and crowded environments. In addition, it is relatively limited for better welfare finishing pig via enriching the pen environment and the space allowance in the commercial farming level. Therefore, stocking densities between 1.05 and 1.35 m2/pig with toy provision can achieve better performance on the production, welfare, and efficiency under the various conditions for finishing pigs.