Light-dark Rhythms during Incubation of Broiler Chicken Embryos and their Effects on Embryonic and Post Hatch Leg Bone Development Carla W. van der Pol*†, Inge A. M. van Roovert-Reijrink*, Conny M. Maatjens*†, Sander W. S. Gussekloo‡, Sander Kranenbarg‡, Jan Wijnen*†, Remco P. M. Pieters‡, Henk Schipper‡, Bas Kemp†, Henry van den Brand† * HatchTech Incubation Technology B.V., P.O. Box 256, 3900 AG Veenendaal, the Netherlands; † Adaptation Physiology Group, Wageningen Institute of Animal Sciences, Wageningen University, P.O. Box 338, 6700 AH Wageningen, the Netherlands; ‡ Experimental Zoology Group, Wageningen Institute of Animal Sciences, Wageningen University, P.O. Box 338, 6700 AH Wageningen, the Netherlands. There are indications that lighting schedules applied during incubation can affect leg health at hatching and during rearing. The current experiment studied effects of lighting schedule: continuous light (24L), 12 hours of light, followed by 12 hours of darkness (12L:12D), or continuous darkness (24D) throughout incubation of broiler chicken eggs on the development and strength of leg bones, and the role of selected hormones in bone development. In the tibiatarsus and femur, growth and ossification during incubation and size and microstructure at day (D)0, D21, and D35 post hatching were measured. Plasma melatonin, growth hormone, and IGF-I were determined perinatally. Incidence of tibial dyschondroplasia, a leg pathology resulting from poor ossification at the bone’s epiphyseal plates, was determined at slaughter on D35. Gildetrom 25 | 3905 TB Veenendaal | The Netherlands | +31 318 512 511 | [email protected] |

Abstract Light-dark Rhythms during Incubation of Broiler Chicken Embryos and their Effects on Embryonic and Post Hatch Leg Bone Development 24L resulted in lower embryonic ossification at embryonic day (E)13 and E14, and lower femur length, and lower tibiatarsus weight, length, cortical area, second moment of area around the minor axis, and mean cortical thickness at hatching on D0 compared to 12L:12D especially. Results were long term, with lower femur weight and tibiatarsus length, cortical and medullary area of the tibiatarsus, and second moment of area around the minor axis, and a higher...