The effects of water deprivation on the behavior of laying hens.

Freedom from thirst is one of the most undeniable welfare requirements. Nevertheless, the welfare implication of water deprivation because of a particular situation (e.g., transport) or as an involuntary consequence (e.g., sick, injured, or subordinate animals) remains unclear. This experiment investigated the behavioral changes in laying hens following various durations of water deprivation by using a motivation test based on passing through a narrow, vertical gap to access water. Twenty laying hens were subjected to water deprivation for various durations (0, 12, 18, 24, or 32 h) and the cost of access was varied by changing the width of the vertical gap (150, 135, 120, or 100 mm) to access the water side of the testing cage. An incomplete randomized block design was used with two tests per hen per wk for 5 wk. The testing apparatus was identical to their home cage but with two cages connected through an adjustable vertical gap and a drinker on the other side. Hens spent more time in the control side rather than the water side at 100 mm compared to 120 mm (P = 0.03). The hens' willingness to pass through a narrow vertical gap in order to access water did not vary according to the duration of water deprivation. Nonetheless, water-deprivation duration had a marked effect on the hens' location and behavior. Hens spent more time in the vicinity of the drinker at 18, 24, and 32 h compared to 0 and 12 h (P < 0.05). Hens spent more time drinking at 24 h and 32 h, followed by 18, 12, and finally 0 h (P < 0.05). Drinking latency and frequency were higher for all water-deprivation durations as compared to the 0 h control (P < 0.05). Water deprivation can be characterized by behavioral changes such as drinking duration, reaching a plateau at 24 h. Complementary physiological data are warranted to fully assess the impact of water deprivation on hen welfare.