Effects of Presorting on Stress Responses at Loading and Unloading and the Impact on Transport Losses from Market-Weight Pigs1

The objective of this study was to determine the effects of presorting before loading on stress responses and transport losses at the slaughter facility in the market-weight pig. A total of 5,802 pigs (n = 33 loads) were used in a randomized complete block design with 2 treatments. The presorted (PRE) and not presorted (NON) treatments each had 292 pigs/pen (0.65 m2/pig). For the PRE treatment, internal swing gates were used to presort pigs manually 18 h before loading, whereas pigs in the NON treatment were sorted from pen mates at the time of marketing. Treatments were assigned to trailer decks in an alternating manner. Data were analyzed using generalized linear mixed model methodology, and loading time was analyzed using mixed model procedures. Loading time differed (P < 0.01) between treatments, with pigs in the NON treatment taking longer to load compared with those in the PRE treatment. During loading, pigs in the PRE treatment had fewer (P < 0.01) incidences of open-mouth breathing and skin discoloration compared with pigs in the NON treatment. However, the incidences of muscle tremors and nonambulatory pigs at loading and the incidences of open-mouth breathing, skin discoloration, and muscle tremors at unloading were not (P > 0.05) different. There were no (P > 0.05) differences between treatments for total losses at the slaughter facility. Two pigs in the PRE treatment and zero pigs in the NON treatment were classified as dead on arrival. In conclusion, presorting market-weight pigs reduced loading time and some stress responses on farm; however, no treatment differences were observed for stress responses or transport losses at the slaughter facility.