Influence of dietary calcium level and particle size of calcium source on in vivo calcium solubilization by commercial Leghorns.

Six experiments were conducted in which hens with oviposition times between 0730 h and 0930 h were intubated with limestone at different levels or particle sizes at time of oviposition. Feed was withdrawn from all hens approximately 15.5 to 17.5 h prior to intubation, and the same feed but without supplemental Ca was immediately returned after limestone intubation. Excrement of each hen was collected from intubation (oviposition) until the next oviposition (24 to 27 h duration) in all experiments except Experiment 4. In Experiment 4, excreta were collected for 25 h after first oviposition. Five hens prior to intubation of Ca source and all hens at termination of an experiment were killed, and the contents of the digestive system were collected. Excreta and digestive system contents were analyzed for total Ca and quantity of insolubilized limestone. Approximately 50% of the Ca found in the excreta from hens with 3.75 g Ca intake was recovered in the same form as ingested (limestone). Percentage of Ca solubilized in the digestive system decreased (P less than .05) as Ca intake increased. Although in vitro solubility of larger limestone particles (2 to 5 mm) was much less than smaller particles (.5 to .8 mm), percentage of Ca solubilized in the digestive system during the 25 h following intubation increased (P less than .05) as particle size increased, suggesting a greater retention time of the larger limestone particles in the gizzard.