Ionic constituents and osmolality of the small intestinal fluids of the laying hen

1. The osmotic pressure of the liquid phase of the contents of the small intestine is always hypertonic to plasma and not affected by egg formation. 2. Chloride concentration is higher during shell calcification, sodium and calcium concentrations increase at the end of shell deposition while calcium concentration shows a cyclic variation with a maximum 18 h after ovulation. 3. The relationships between the ions and water of the duodenum and upper jejunum are modified by egg formation: the apparent reduction of Na+ and W+ is compensated by an increase in Ca2+. 4. It is concluded that egg formation acts on the intestinal composition via the proventriculus and gizzard rather than through a direct effect on the intestine.