The impact of daylength on turkey productivity, health and behaviour

The impact of graded levels of daylength on the productivity, health and behaviour of hens and toms was studied in two experiments to 18 wk of age. Daylength treatments (trt) were 14 (14L), 17 (17L), 20 (20L) and 23 (23L) h and were started at 10 d of age. Turkeys (720 hens and 480 toms) were randomly allocated to 8 rooms (2 rooms per lighting trt) with six pens (3 hen and 3 tom) per room in each experiment. Body weight (BW) and feed consumption (FC) were assessed throughout the trial and feed efficiency (G:F; g of gain/g of feed) calculated from BW and FC values. Birds were checked daily for mortality and culls, and affected birds sent for necropsy. Bird well-being was evaluated by gait score (GS), the incidence of foot pad dermatitis (FPD), breast buttons and blisters, ocular size and pressure, and tom behavioural observations. Data were analyzed using SAS 9.3 based on a completely randomized design nested within four daylengths. Regression analysis established relationships between response criteria and daylength. Differences were considered significant at P≤0.05 and trends noted at P≤0.10. At 21 and 42 d, body weight increased linearly with daylength, but by 84 d tom weights decreased in a quadratic fashion and hen weights were unaffected by daylength. At 126 d, both male and female weights decreased linearly with increasing daylength, with the magnitude of the response gender dependent. Feed consumption corresponded to body weight changes, increasing for d 10-21 and 21-42, and decreasing for d 63-84, 84-105, and 105-126 with increasing daylength. Feed efficiency (G:F) was not affected by daylength for 10-84, 10-105 and 10-126 d periods. The incidence of mortality and culling was not affected by daylength for the 10-84 d period, but increased in a quadratic manner with increasing daylength for the 10-105 and 10-126 d periods. The incidence of skeletal disorders (valgus-varus and rotated tibia), injurious pecking and pendulous crops (females only) increased linearly with increasing daylength. Average GS increased linearly with daylength at 11 and 17 wk for both hens and toms, but the effect was larger in toms. Daylength did not affect FPD, but more lesions and more severe scores were found for hens than toms. The presence of breast buttons and blisters increased linearly with daylength (11 wk) with the effect on blisters predominately seen in toms. Eye weight increased and corneal diameter decreased linearly with increasing daylength at 12 and 18 wk. Dorso-ventral and media-lateral diameter, and anterior to posterior depth exhibited a quadratic relationship with the highest values seen for the 23L trt. Ocular pressure was not affected by daylength. Over 24 h of behavioural observation (both photo- and scotoperiod), resting increased, and walking, and environmental and feather pecking decreased with increasing daylength. During the photoperiod, inactive resting increased and feeding, drinking, standing, walking, preening, and environmental and feather pecking behaviours decreased as daylength increased. To conclude, daylength affects the growth and feed intake of turkeys in an age and gender specific manner, and mortality and culling increase with longer daylength. Health and welfare parameters are also affected by daylength with 23L demonstrating poorest overall bird well-being