Project 2.3

The first funding period clearly revealed physiological, genetic, transcriptional and endocrine differences of the two contrasting high-yielding laying hen strains. Results raise the demand for an in-depth differentiation of strain-specific strategies of endogenous myo-inositol and P utilization. This requires data beyond the gastrointestinal tract, i.e., the initial inositol phosphate cleavage and P uptake.

In addition to jejunum, this project therefore aims to analyse organs and tissues involved in mineral storage and excretion, i.e. medullary bone, kidney, and liver. Special emphasis is given to existing sample material from the first funding period. Moreover, based on the results from the longitudinal analysis of the first funding period, this project further focuses on the transition from pre-laying throughout the onset of laying. Analyses of genetic differences in P utilization (PU) between LB and LSL laying hens will aid in elucidating the transcriptional and genetic foundation of these differences. Taken together, this project delivers measurements of transcriptional and endocrine parameters related to mineral utilization based on dynamics of mineral homeostasis.

The following hypotheses are addressed:
1. Genetic differences between LSL and LB laying hens culminate in strain-specific patterns of hub genes and pathways, e.g. of P homeostasis, that ultimately affect PU.
2. Endogenous renal myo-inositol synthesis is reduced by nutritive myo-inositol supplementation. The overall myo-inositol pool modulates energy metabolism.
3. At the onset of egg laying, especially under dietary P deficiency, hens prompt endogenous compensatory responses that ensure the physiological mineral balance.