Effect of target slaughter weight on production efficiency, carcass traits and behaviour of restrictively-fed gilts and intact male finisher pigs

The effect of 3 slaughter weights (85.95 or 105 kg) on performance and carcass traits of 481 pigs in single-gender groups of 13 (18 groups of gilts and 19 groups of intact males) was evaluated. Pigs (39.5 +/- 3.3 kg) were fed a liquid diet 3 times daily in a long trough. The behaviour of pigs slaughtered at 105 kg was recorded at 50, 60 and 70 days after the start of the experiment (5 groups of gilts and 4 groups of intact males). Behaviour (active, inactive, feeding) and posture (standing, lying, dog-sitting) of all pigs was recorded at 5-min intervals for 30 min prior to and 1 h after each feeding event. Slaughtering pigs at 95 kg and 105 kg delayed production by 7 and 16 days, respectively, compared to slaughtering at 85 kg (P<0.0001). Gilts needed 4 days more than males to reach each slaughter weight (P<0.01), and chilled carcass weights increased with increasing slaughter weight (P<0.0001). Daily feed intake and gain were not affected by slaughter weight: however, gain-to-feed ratio increased in males with increasing slaughter weight while the inverse was observed in gilts (P<0.01). The kill-out percentage was greater at the heavier weights (P<0.05). Backfat depth increased in males with increasing slaughter weight (P<0.01) but there was no change in females (P>0.05). Muscle depth increased with increasing slaughter weight (P<0.05) and therefore lean meat yield did not change. Behaviour did not differ between genders on the 3 days of observation, but the proportion of time spent active and standing before feeding increased as pigs grew from day 50 to 70 (P<0.05). The proportion of posture changes was greater before than after feeding (P<0.001). Results of this study indicate that slaughtering intact male pigs at heavier weights improved growth performance but increased fat depth. Conversely, gilts were less efficient at converting feed into body weight at the heavier weights but carcass traits were not modified as slaughter weight increased. In the latter part of the finishing period, competition for access to the trough probably increased as trough space allowance decreased, and the increase found in standing before feeding could reflect an attempt by the pigs to gain immediate access to the feed. (C) 2010 Elsevier B.V. All rights reserved.