Date Full Report Received08/23/2007
Date Abstract Report Received08/23/2007
Funded ByNational Pork Board
Pork producers have often been told that stressing pigs can not only have negative consequences on the pig’s welfare but also on the quality of pork that they generate. Removing pigs from their familiar environment, loading them on a trailer, trucking them to a packing plant, unloading them, and leaving them in an unfamiliar pen most definitely introduces stress on the animal. The objective of this study was to evaluate these pre-slaughter stressors, looking at location in the trailer, specifically the top or bottom deck of a traditional pot-bellied trailer, a short (3 hours) or long (6 hours) haul, and a short (3 hours) or long (6 hours) lairage at the packing plant. Since weather conditions will also introduce a level of stress under these three circumstances, we evaluated deck location, haul duration, and time in lairage during four distinct seasons of the year; winter, spring, summer, and fall. The concentration of the stress hormone cortisol was evaluated for each pig in the study. Higher levels of cortisol at the time of bleeding were considered an indication that the animal was stressed. Mixed commercial crossbred market hogs (PIC, Franklin, KY) were used in this study. The dates and number of pigs harvested in this study are as follows: February 14 and 16, 2006 (n = 599), May 16 and 18, 2006 (n = 660), August 1 and 3, 2006 (n = 649), and October 17 and 19, 2006 (n = 661). Climatic conditions (temperature and relative humidity) in the trailer were monitored at one minute intervals using portable data recording devices located in the three compartments (front, middle, rear) of the top and bottom decks of the trailer. All pigs came from the same commercial source and identical transport protocol, data collection techniques, and slaughter procedure was repeated on Tuesday and Thursdays within the same week of each seasonal slaughter. Blood was collected from each carcass when they were stuck on the bleed table for determining serum cortisol concentration. Fresh pork loins were collected from the loin line during carcass processing and fresh pork quality parameters were evaluated for objective color recording L* (color lightness), a* (redness), and b* (yellowness) values, loin muscle pH, and the percentage drip loss over a 24 hour period. We evaluated statistical differences between the averages of each quality parameter and blood cortisol concentrations for differences between deck location, transport duration, length of lairage, and the seasonal effects. We also separated the data further looking at each transport variable within the season of the year. The range of temperature and humidity recorded in the trailer during the long haul was greatest during the winter season, with the bottom front compartment showing the most fluctuation. Climatic conditions within the trailer during the short haul had a wider range of temperature during the fall season transport. Climatic conditions in the bottom deck, front compartment were often the most unfavorable for pig welfare during the summer haul as the temperature and humidity often reached a point putting the pigs in an “emergency” category of the Weather Safety Index. More research is necessary in the U.S. to evaluate climatic conditions of the various trailer compartments with regard to market hog welfare and ultimate pork quality. Stress, as indicated by the level of cortisol in the blood, was the greatest during the summer and fall seasons and pigs transported a longer duration had higher cortisol concentrations in their blood (indicating greater stress). Short or long lairage didn’t matter during the spring, yet in the winter and fall seasons, short lairage was more stressful as indicated by higher cortisol levels. In contrast, a longer lairage in the summer season resulted in higher cortisol levels. This indicates that to improve pig welfare (reduce stress) in the summer months, a shorter lairage is beneficial. We classified loins as pale, soft, and exudative (PSE) if they had a 24 hour drip loss greater than 5% and a lightness score (L*) greater than 55. Keep in mind that a higher L* value is more pale and an L* of 100 is white. We found that pigs transported in the bottom deck (regardless of duration traveled or time spent in lairage) had a higher rate of PSE loins (6.94%) in the winter compared to loins from pigs that were transported in the winter on the top deck (3.58%). Furthermore, pigs removed from the bottom deck of the trailer that went into a short lairage (3 hours) prior to slaughter generated 5.28% PSE loins while the pigs that came off the bottom deck into a long (6 hour) lairage generated only 2.86% PSE loins. This indicates that at least part of the potential for developing PSE loins may be alleviated by providing pigs with a longer lairage prior to slaughter.