Effects of animal handling and transportation factors on the welfare, stress responses, and incidences of transport losses in market weight pigs at the packing plant

The objective of this dissertation was to determine the causes of dead and non-ambulatory pigs at US packing plants and to identify management strategies to reduce these transport losses. Four studies involving a total of 297 trailer loads of market weight pigs (n = 42,283) were conducted within a Midwestern US production system to determine the effects of various pre-slaughter stressors and management strategies on physical indicators of stress (at loading and unloading) and transport losses. Pigs were loaded using commercial procedures and were transported 2 to 4 h to a commercial packing plant. Three studies established that transport losses were minimized when pigs were provided with transport floor spaces of 0.46 m2/pig or greater. However, the effects of transport floor space on transport losses were dependent upon season in one study, and this warrants additional research. Distance moved during loading was evaluated in two separate studies. Both studies demonstrated that pigs moved long distances (47 to 91 m) had 2-fold higher (P < 0.01) rates of open-mouth breathing during loading than pigs moved short distances (0 to 30 m), but distance moved during loading did not affect transport losses at the plant. The effects of mixing unfamiliar pigs during transport (mixed vs. unmixed) and feed withdrawal prior to loading (0 vs. 24 h) were evaluated. Although not statistically significant, transport losses were numerically reduced by ∼50% for pigs that were fasted 24 h prior to loading and for pigs that were not mixed during transport. Trailer design (pot-belly vs. straight deck) and season did not affect (P > 0.05) total transport losses, but the incidence of total non-ambulatory pigs was higher (P < 0.05) in the winter than in the spring and summer. A fifth study involving 64 market weight pigs at the University of Illinois Swine Research Center established that pre-slaughter stressors (aggressive handling, restricted transport floor space, and long distances moved) have additive effects on rectal temperature, blood acid-base balance, and longissimus lactate concentrations. Collectively, these studies identify causes of transport losses and demonstrate that it is possible to handle and transport pigs with minimal stress responses.