Effects of grow-finish group size on stress responses at loading and unloading and the effect on transport losses from market-weight pigs

Abstract

<h2>ABSTRACT</h2> The objective of this study was to determine the effects of grow-finish group sizes on stress response and transport losses from the market-weight pig. A total of 4,522 pigs (122.0 ± 10.6 kg; n=26 trailer loads of pigs) were used in a randomized complete block design. In the grow-finish barn, the small group size (SG) treatment had 36 pigs per pen, whereas the large group size (LG) treatment had 324 pigs per pen. Floor space and feeder space were standardized across treatments. Market-weight pigs were sorted from pen mates at loading and mixed with unfamiliar pigs during transport. Treatments were assigned to trailer decks in an alternating manner. Loading time, physical signs of stress, and transport losses were monitored by treatment. Loading time was analyzed using mixed model procedures, and stress responses were analyzed using generalized linear mixed model methodology. Loading time differed (P < 0.01) between treatments, with LG taking longer to load than SG. The SG size had lower incidences of (P < 0.01) open-mouth breathing and skin discoloration during loading, but there were no differences (P < 0.05) in incidence of muscle tremors or nonambulatory pigs at loading. At the slaughter facility, LG had a lower incidence of skin discoloration (P < 0.01); however, there were no differences (P > 0.05) for open-mouth breathing or muscle tremors. There were no differences for dead on arrival, nonambulatory pigs, or total losses. In summary, group size does not appear to affect the incidence of transport losses.