Behavioral Differences of Laying Hens with Fractured Keel Bones within Furnished Cages

Teresa M. Casey-Trott, Tina M. Widowski

High prevalence of keel bone fractures in laying hens is reported in all housing systems. Keel fractures have been associated with pain and restricted mobility in hens in loose housing. The objective was to determine whether keel fractures were associated with activity of hens in furnished cages. Thirty-six pairs of LSL-Lite hens (72 weeks) were enrolled in the study. One hen with a fractured keel and one hen without were identified by palpation in each of 36 groups of hens housed in either 30- or 60-bird cages stocked at 750 cm(2)/hen. Behavioral activity of each hen was recorded by four observers blind to keel status using focal animal sampling for 10 min within a 2-h period in the morning (08:00-10:00), afternoon (12:00-14:00), and evening (17:00-19:00). All hens were observed during each of the three sample periods for 3 days totaling 90 min, and individual hen data were summed for analysis. Hens were euthanized 48 h after final observations, dissected, and classified by keel status: F 0 (no fracture, N = 24), F 1 (single fracture, N = 17), and F 2 (multiple fractures, N = 31). The percentages of time hens performed each behavior were analyzed using a mixed procedure in SAS with fracture severity, body weight, cage size, rearing environment, and tier in the model. Fracture severity affected the duration of perching (P = 0.04) and standing (P = 0.001), bout length of standing (P < 0.0001), and location (floor vs. perch) of resting behaviors (P = 0.01). F 2 hens perched longer than F 0 hens, 20.0 ± 2.9 and 11.6 ± 3.2%. F 2 hens spent less time standing, 15.2 ± 1.5%, than F 0 and F 1 hens, 20.7 ± 1.6 and 21.6 ± 1.8%. F 2 hens had shorter standing bouts (22.0 ± 4.2 s) than both F 0 and F 1 hens, 33.1 ± 4.3 and 27.4 ± 4.4 s. Non-fractured hens spent 80.0 ± 6.9% of total resting time on the floor, whereas F 1 and F 2 hens spent 56.9 ± 12.4 and 51.5 ± 7.7% resting on the floor. Behavioral differences reported here provide insight into possible causes of keel damage, or alternatively, indicate a coping strategy used to offset pain or restricted mobility caused by keel fractures.