The impact of graded levels of daylength on turkey productivity to eighteen weeks of age

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The impact of graded levels of day-length on the productivity of hens and toms was studied in two trials. Daylength treatments (trts) 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 - 30 per pen and 3 tom - 20 per pen) per room in each trial. Body weight (BW) was assessed at 0, 10, 21, 42, 63, 84, and 126 d of age; feed consumption (FC) was measured for the time periods between body weight determinations and feed efficiency (G:F; g of gain/g of feed) was calculated from BW and FC values. Birds were checked daily for mortality and culls, and affected birds were sent for necropsy. Data were analyzed according to a completely randomized block design with trial as the block and rooms nested within lighting trts. Regression analysis was used to study the relationship between dependent variables and daylength. Significance was declared at P ≤ 0.05 and trends at P ≤ 0.10. At both 21 and 42 d, body weight increased linearly with increasing daylength. At 84 d weights of toms decreased in a quadratic fashion and hen weights were unaffected. At 126 d, both tom and hen weights decreased linearly as daylength increased, with the magnitude of response gender dependent. Feed consumption corresponded with body weight changes, increasing for d 10 to 21, and 21 to 42 and decreasing for d 63 to 84, 84 to 105, and 105 to 126 with increasing daylength. Feed efficiency (G:F) was not affected by daylength for 10 to 84, 10 to 105 and 10 to 126 d periods. The incidence of mortality and culling was not affected by daylength for the 10 to 84 d period, but increased in a quadratic manner with increasing daylength for the 10 to 105 and 10 to 126 d periods. 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.

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