Effects of seasonal environment, on-farm handling, transport stocking density, and time in lairage on body temperature, serum cortisol levels, and pork lean quality of market hogs

The objective of this study was to evaluate the effect of three seasonal environments: temperate (TMP), cold stress (CS), and heat stress (HS), two on-farm handling intensities: conventional (CONV) and passive (PAS), two transport stocking densities: tight (TSD) and loose (LSD), and two lairage lengths: 45 min and 3 h, on digestive tract temperature, pork quality, and blood serum cortisol levels. Market hogs were harvested at three representative environmental situations: (TMP) 6 to 13°C, (n = 111), (CS) -9 to 0°C (n = 113), and (HS) 22 to 35°C (n = 112). At 16 h prior to harvest, a computer-activated temperature logging device (Ibutton, Dallas Semiconductor Corp. Dallas, TX) was swallowed by the market hogs. Half were randomly subjected to PAS and the other half CONV, with each group being loaded on trailers of identical dimensions. During loading, approximately half of the pigs were allotted to a TSD (0.32 m2/100kg) and the other portion to a LSD (0.4 m2/100kg). After a 2.5 h transport to the harvest facility, half of the pigs within each trailer were randomly given one of two lairage treatments. Blood was collected at exsanguination for subsequent cortisol analysis. Ibuttons were collected from the viscera at harvest and loin lean quality data was collected after 24 h chill. Prior to handling, CS pigs had higher digestive tract temperatures than pigs from the HS and TMP harvests. During lairage, HS pigs had higher digestive tract temperatures than TMP pigs, which had higher temperatures than CS pigs. This suggests the pigs' activity in lairage accelerated the metabolism of the HS pigs. Pigs from the HS harvest given 3 h of lairage had higher cortisol levels than TMP pigs given 3 h of lairage; and, HS and TMP pigs given 3 h of lairage had higher cortisol levels than HS and TMP pigs given 45 min of lairage, suggesting a 3 h lairage exacerbates heat stress. Pigs from the HS harvest had paler loins than CS and TMP pigs and greater loin purge loss percentages than CS pigs, implying that high ambient temperatures accelerated metabolic muscle rate. Pigs given CONV and a LSD had darker loins than all PAS pigs and CONV pigs given a TSD, suggesting CONV handling, when in combination with a TSD, could result in chronic glycogen depletion. Pigs given a 45 min lairage had higher 30 h loin pH values and darker loins than pigs given a 3 h lairage, suggesting the 45 min lairage eliminated the opportunity for fighting in lairage, ultimately improving lean quality. A CONV handling intensity and (or) a TSD have negative affects on digestive tract temperature, blood serum cortisol levels, and lean quality traits. However, the most dramatic impact on the aforementioned traits occurred when pigs were given a 3 h lairage during the HS harvest. Pigs should be kept in lairage less than 3 h during periods of heat stress to minimize digestive tract temperature and ultimately improve swine welfare and lean quality.