Effect of rest duration on recovery from repeated exercise in near-market-weight pigs

The process of transportation can be seen as a succession of stressors, from which pigs may not have time to recover before slaughter. The aim of this study was to determine the extent to which the duration of the rest time given to near-market-weight pigs after an initial exposure to exercise affected their recovery from subsequent exercise. Eighteen groups of 3 gilts were exercised (Ex1) through a standard handling course, including two 19° ramps, and then were held in a holding pen for either 35 (RT35), 75 (RT75), or 150 (RT150) min (Rest Period 1, RP1). Afterward, pigs were exercised a second time (Ex2) and left to rest for 150 min. Recovery from Ex2 (Rest Period 2, RP2) was assessed using measures of heart rate (HR), respiratory rate (RR), skin temperature (ST), and posture. Repeated measures and regression analysis were used to analyze the data. For RT75 pigs, there were no detrimental effects of Ex2 on HR, RR, and handling time (P > 0.05, for all) during the exercise and recovery periods. Skin temperature during Ex2 was greater than ST during Ex1 (P < 0.001), whereas ST during RP1 did not differ from ST during RP2 (P > 0.05). Doubling the rest period did not provide any more beneficial effects in regard to RR and HR (P > 0.05 for both) during Ex2 and RP2 compared to RT75 pigs, as shown by the similar latencies to recover for these 2 variables. However, ST did not increase between exercises, and RT150 pigs required less time to complete the handling course during Ex2. The results show that a lack of rest after an initial exposure to exercise made pigs more susceptible to stress during Ex2 and RP2, as demonstrated by greater (P < 0.001 for all) HR, RR, and ST during RP2 compared to RP1 and Ex2 compared to Ex1. When given more than 35 min to rest during RP2, RT35 pigs eventually recovered. Latencies of recovery for HR, ST, RR, and posture were all greater (P < 0.05 for HR, ST, and RR and P < 0.001 for posture) than those obtained for RT75 and RT150 pigs. This study highlights that if pigs are not initially given enough rest to recover from exercise, a subsequent exposure to the same exercise will cause an increase in these physiological variables during exercise and recovery. Further research is needed to investigate factors contributing to the quality of rest, with a particular focus on conditions not allowing a proper rest on the truck or in lairage.