The objective of this study was to determine the effects Therefore, the objective of this study was to determine the effects of pre-sorting on stress responses at the time of loading and unloading and how it impacts transport losses in the market weight pig. This study took place between December and March. Thirty three loads of mixed sex market weight pigs (n = 5802) from three conventional grow-finish sites were used in a randomized complete block design. Each site had two rooms with both treatment groups represented in each room. The large pen, pre-sorted (LPS) treatment had 292 pigs/pen (0.67m2*pig -1). LPS pigs were sorted from pen mates ~18 h prior to loading. The large pen, not pre-sorted treatment (LNPS) also had 292 pigs/pen (0.67m2*pig-1). LNPS pigs were sorted from pen mates at the time of marketing. Pigs were moved in groups of four to six using sort boards and electric prods, when necessary. Treatments were randomly assigned to a trailer deck (~0.41 m2*pig-1). Straight deck trailers were used and pigs were transported ~1 h to a commercial harvest facility. During loading and unloading, the number of pigs displaying open mouth breathing (OMB), skin discoloration (SD), and muscle tremors (MT) were recorded. At the plant, dead and non-ambulatory pigs were recorded during unloading, and total losses were defined as the sum of dead and nonambulatory pigs at the plant. Data was analyzed using Proc Glimmix of SAS. Statistical analysis could not be run on the incidence of deads on arrival (DOA) because there were too many zeros in the dataset. LPS had two DOA’s (0.07%) and there were no DOA’s in the LNPS treatment. LPS pigs had lower (P ≤ 0.0001) OMB and SD during loading compared to LNPS pigs. There were no (P > 0.05) differences for MT or non-ambulatory at loading or for stress responses at unloading. No (P > 0.05) differences between treatments for fatigued, injured, total non-ambulatory or total losses existed. In conclusion, pre-sorting market weight pigs had some effect on reduced OMB and SD on farm; however, there were no differences for OMB, SD and MT or transport losses at the plant.
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