The effect of water sprinkling on behavior and core body temperature of market hogs transported during summer

Hogs are often transported to slaughter under conditions exceeding their thermo-neutral zones, which can lead to reduced welfare and increased in-transit loss. Water sprinkling during lairage decreases micro-climate and hog body temperatures and improves welfare, but there is no clear evidence of these effects during transport. The aim of this study was to observe if sprinkling hogs in stationary trailers before and after transport decreased signs of heat stress. In each of 12 weeks from May to September 2011, 2 pot-belly trailers with 208 hogs per trailer were transported 2h to slaughter. One was outfitted with a custom made sprinkler system that ran for 5min (~125 L) immediately before departure from the farm and immediately before unloading at the plant. In each trailer, 4 test compartments (1 on the top deck, 2 on the middle deck, and 1 on the bottom deck) were outfitted with cameras, and the core body temperature (CBT) of 4 randomly chosen hogs (n = 384) in each were recorded using orally administered iButtons. Trailer and deck loading order were randomized. Behaviors during transport, unloading and during lairage were recorded from video or live observations. Data were analyzed through ANOVA with ambient temperature external to the truck (AmbT) as a co-variant. AmbT averaged 19.5°C ± 3.8°C (range: 14–26°C). At AmbT > 23°C, there was no effect of sprinkling on behavior on-truck (standing, sitting or lying), but at AmbT < 23°C, more hogs stood on sprinkled trucks (P < 0.05). Sprinkling did not affect slips or falls during unloading. In lairage, latency to lie was shorter when AmbT exceeded 23°C (P < 0.05) and sprinkled hogs spent more time lying and less time sitting (P < 0.05) and had fewer drinking bouts than controls (P < 0.0001) regardless of AmbT. CBT increased between loading and departure and decreased while in transit for all hogs (P < 0.0001) and sprinkling further reduced CBT at arrival at AmbT > 23°C (P < 0.05). Therefore, sprinkling hogs when ambient temperature exceeds 23°C can help to alleviate transport-related heat stress without detrimental effects on unloading.