Date Full Report Received03/31/2006
Date Abstract Report Received07/25/2007
InvestigationInstitution: University of Missouri-Columbia
Primary Investigator: Eric Berg
Co-Investigators: Chadwick Carr
Funded ByNational Pork Board
This research was conducted to evaluate the effect of three seasons of the year: fall, summer, and winter, how pigs were handled on-farm: aggressive yet conventional and very easy, two transport stocking densities: tight and loose, and two resting periods at the plant prior to harvest: 45 min and 3 h, on the digestive tract temperature and cortisol in the blood of market hogs. The day before harvest, a computer-activated temperature logging device (Ibutton), was placed down the throat of the market hogs. Half of all hogs were handled very easily on the farm and the other half were handled more aggressively. As pigs were loaded, approximately half of the pigs were loaded at a tight stocking density, (all pigs could not lie down at the same time, 0.4 m2/pig) and the other portion were loaded at a looser density (all pigs could lie down at the same time, 0.5 m2/pig). When arriving to the packinghouse, half of the test animals were harvested after a 45 min rest and the other half after a 3 h rest. Blood was collected at bleeding for testing cortisol. Ibuttons were collected from within the gut after harvest.
Prior to handling, pigs from the winter harvest had higher digestive tract temperatures than pigs from the other two harvests. However, during handling, pigs from the summer harvest that were handled more aggressively did not have different digestive tract temperatures than pigs from the winter harvest that were handled very easily. This suggests that more aggressive handling accelerated the body metabolism of the summer pigs, raising their digestive tract temperature. During pre-harvest resting, pigs from the summer harvest had higher digestive tract temperatures than pigs from the fall harvest, which had higher temperatures than pigs from the winter harvest. This suggested that the hot environment combined with fighting and mixing at the packing plant accelerated the metabolism of the summer pigs. Most pigs subjected to the longer pre-harvest rest period had higher digestive tract temperatures than pigs subjected to the shorter resting period. The results for season and rest period prior to harvest were similar to the digestive tract temperatures. Cortisol concentrations were higher from pigs given the longer resting period. Additionally, pigs from the summer harvest had a higher coritsol concentration than pigs from the other two harvests.
Overall, pigs harvested in the winter began the day trying to maintain heat and body temperature, so they had the highest digestive tract temperatures prior to handling and trucking. By the time they were harvested, their activity raised their temperature, and they no longer needed to conserve heat, so their digestive tract temperature went down. Pigs harvested in the summer began the day trying to get rid of body heat (cool down), so they had the lowest digestive tract temperatures prior to handling and trucking. By the time they were harvested, their activity combined with heat stress raised their body temperature to a point that they were not able to get rid of all the added body heat, so they had the highest digestive tract temperatures during the resting period prior to harvest. Additionally, the higher cortisol concentration from the summer group suggests their level of welfare may be lower than pigs from the other two harvests. Additionally, digestive tract temperatures and blood cortisol concentrations were higher from the pigs given the longer pre-harvest resting period, especially during the summer harvest. Collectively, it appears that during times of summer heat stress, pigs should not be allowed to rest as long to prevent further fighting and restlessness at the plant. The other solution may be to rest the pigs longer than 3 h prior to harvest to allow them to more fully recuperate from previous stresses. However, that conclusion cannot be made from this experiment since we did not evaluate body temperature of the pigs at the packing plant longer than 3 hours.