Phytase has long been used to decrease the inorganic phosphorus (Pi) input in poultry diet. The current study was conducted to investigate the effects of Pi supplementation on laying performance, egg quality and phosphate–calcium metabolism in Hy-Line Brown laying hens fed phytase. Layers (n = 504, 29 weeks old) were randomly assigned to seven treatments with six replicates of 12 birds. The corn–soybean meal-based diet contained 0.12% non-phytate phosphorus (nPP), 3.8% calcium, 2415 IU/kg vitamin D3 and 2000 FTU/kg phytase. Inorganic phosphorus (in the form of mono-dicalcium phosphate) was added into the basal diet to construct seven experimental diets; the final dietary nPP levels were 0.12%, 0.17%, 0.22%, 0.27%, 0.32%, 0.37% and 0.42%. The feeding trial lasted 12 weeks (hens from 29 to 40 weeks of age). Laying performance (housed laying rate, egg weight, egg mass, daily feed intake and feed conversion ratio) was weekly calculated. Egg quality (egg shape index, shell strength, shell thickness, albumen height, yolk colour and Haugh units), serum parameters (calcium, phosphorus, parathyroid hormone, calcitonin and 1,25-dihydroxyvitamin D), tibia quality (breaking strength, and calcium, phosphorus and ash contents), intestinal gene expression (type IIb sodium-dependent phosphate cotransporter, NaPi-IIb) and phosphorus excretion were determined at the end of the trial. No differences were observed on laying performance, egg quality, serum parameters and tibia quality. Hens fed 0.17% nPP had increased (P < 0.01) duodenum NaPi-IIb expression compared to all other treatments. Phosphorus excretion linearly increased with an increase in dietary nPP (phosphorus excretion = 1.7916 × nPP + 0.2157; R2 = 0.9609, P = 0.001). In conclusion, corn–soybean meal-based diets containing 0.12% nPP, 3.8% calcium, 2415 IU/kg vitamin D3 and 2000 FTU/kg phytase would meet the requirements for egg production in Hy-Line Brown laying hens (29 to 40 weeks of age).

Upcoming nesting behaviour traits, such as the exact oviposition time or the time spent in the nest, have a direct impact on economically relevant aspects. Hens which stay for a long time inside the nest box, require more nest capacity which result in higher investments for the farmer. This is similar to flocks in which most of the layers have the need to lay their eggs in a short time frame during the day. For both of these nesting behaviour traits, published data have shown strain differences. While brown layers are more relaxed in terms of their oviposition time, almost 90% of a white layer flock lay their eggs within 3 hours during the morning. Additionally, a white layer on average occupies the nest 15 minutes longer than a brown layer. The estimated heritabilities for both traits are on a medium level of around h² = 0.25, and are therefore susceptible to genetically-linked changes. Lower heritabilities are estimated for indirect nesting behaviour traits such as the time interval between two consecutively laid eggs (h² = 0.09) or the total clutch size (h² = 0.25). Ranging behaviour traits also show heritabilities on a medium level. The published heritability for the frequency of passages as well as for the length of stay in the winter garden is h² = 0.24, however, their relationship to the most important selection trait ‘egg number’, is negative. The laying performance tested with the Funnel Nest Box (FNB) show differences to the recorded egg number of full sibs which have been tested in cages. Tabled genetic parameters showed low correlations for the egg number at peak production (rg = +0.2 to rg = +0.4) which could be explained by genotype x environment effects. Other traits like egg weight, early egg production and body weight show high correlations between both testing environments.