The effects of limestone particle size on bone health and performance of pullets and hens in conventional cage and alternative housing systems

One of the major welfare issues in cage-free housing systems is bone fracture. The goal of this research was to improve bone health in layers by building better pullet skeletons and to investigate limestone particle size (LPS) effects on bone health in conventional cages and cage-free housing systems. Study 1 was a preliminary study that compared conventional cages with litter floor pens in terms of performance, bone health, and eggshell quality from 33 to 47 wk of age. Caged hens had higher egg production and eggshell strength, and improved feed efficiency, but lower tibia bone mineral content compared to floor housed hens. Study 2 examined the effects of LPS fed from 7 to 17 wk of age on performance and bone health in conventional cage and aviary systems. The use of a limestone blend of fine and large particles (0.879 mm; LPS-Blend) rather than a fine limestone (0.431 mm; LPS-Fine) increased tibia bone mineral density (BMD) and alleviated incidence of curved keel bones at the end of the pullet phase. Study 3 investigated the subsequent effects of LPS (Study 2) during the layer phase. The LPS-Blend increased eggshell weight and alleviated keel bone indentations in the middle and end of the lay cycle (Study 3). Study 4 examined the effects of LPS fed from 9 to 17 wk of age on pullet and hen performance, bone health, and eggshell quality in deep litter systems. Hens fed LPS-Blend during the pullet phase had greater tibia BMD at onset of egg production and higher overall eggshell strength. Study 5 evaluated the effect of two layer strains on nest and perch use in aviary systems. White Leghorn hens had greater usage of perch and nest and preferred elevated tiers compared to Brown hens. In conclusion, the provision of LPS-Blend rather than LPS-Fine during the pullet phase improved bone mineralization at the onset of egg production and eggshell quality. Although White Leghorn hens had greater usage of resources in aviary systems; they had higher potential risk of bone fractures