A study was conducted to investigate the effect of 1,25-dihydroxyvitamin D3 (calcitriol) and sunlight exposure of hens during the laying period (18-74 weeks) on laying hen performance, egg quality, and bone quality. A total of 240 Lohmann Brown laying hens were used in a randomized block trial with 4 treatments (A, B, C, D), 3 replicates per treatment, and 20 birds per replicate. Treatments were: (A) 75 µg/kg Vit D3 as control + indoor rearing, (B) control with additional 1.0 µg/kg calcitriol + indoor rearing, (C) control + once-weekly access to pasture, (D) control with additional 1.0 µg/kg calcitriol + once weekly access to pasture. We measured egg production, feed consumption and egg quality. At 74 weeks of age, 24 laying hens from each treatment were randomly selected, weighed, euthanized, and the femur, tibia, humerus, and keel bone were harvested to measure bone length, diameter, weight, and breaking strength. Neither calcitriol nor sun exposure affected (p⡥0.05) body weight, feed intake, bone diameter, bone density, and bone breaking strength. The addition of calcitriol resulted in significantly (p˂0.05) darker egg shells and less intensely coloured yolks in hens in treatments B and D compared to treatment A eggs. Hens of treatment D laid eggs with significantly weaker and thinner shells compared to hens of treatment B. Contrary to initial expectations, the supplementation of calcitriol and exposure of the hens to sunlight during the laying period did not reduce the prevalence of keel bone fractures.
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