Plasma inorganic phosphorus concentration during egg‐shell formation: Effect of the physical form of the dietary calcium

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Abstract
Four experiments were carried out with Warren laying hens to elucidate the changes in plasma Pi concentration during egg formation. In hens receiving a normal diet containing a Ca supplement in a powdery form, Pi increased from 25-42 mg/l during an entire shell formation cycle (from 10-22 h after oviposition of the previous egg), while Pi decreased slightly in cockerels during the night. This increase in Pi in hens was not related to cessation of feeding at the onset of darkness, but was specifically connected with the beginning of shell secretion. When hens received Ca as crushed sea-shells separately from the diet, the nocturnal peak in Pi virtually disappeared and only a temporary increase of 4 mg/l between 10-14 h after oviposition remained. Apparently the beginning of shell secretion is always accompanied by an increase in Pi and a separate presentation of dietary Ca reduces the bone mobilization at night.