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Influence of Dietary Phosphorus and Vitamin D₃ Levels on In vivo Limestone Solubilization, Plasma Calcium, and pH of the Digestive Tract of Leghorn Hens at Oviposition and During Egg Cycle

Poultry Science Department and Alabama Agricultural Experiment Station, Auburn University, Auburn, AL 36849; Phone: (205) 844-4133; FAX: (205) 844-2641

Correspondence: D. A. Roland, Sr.

Five experiments were conducted to determine the influence of dietary phosphorus (P) and vitamin D₃ (cholecalciferol) levels on in vivo limestone solubilization, plasma calcium (Ca) level and pH of the digestive tract at oviposition and during egg cycle. In Experiment I, White Leghorn hens were fed 0.4 or 0.7% total P for 6 weeks and then intubated with 0, 5.3, or 10.6 g limestone (0, 2 or 4 g Ca) at first oviposition. Excrement from each hen was collected from first oviposition until subsequent oviposition. Blood samples were collected and digestive tracts removed. Excrement and digestive tract contents were analyzed to determine the extent of limestone solubilization. In Experiments II and III, hens were fed 0.3, 0.45, or 0.6% or 0.3, 0.5 or 0.7% total P, respectively, prior to deeding of limestone. In Experiment IV, pH of the digestive tract was measured in hens (fed 0.3, 0.5 or 0.7% P for six weeks prior to pH measurement) at oviposition and 4, 8, 12, 16, 20 and 24 hours post oviposition. In Experiment V, hens were fed diets containing 200 or 500 ICU/kg of vitamin D₃ for six weeks, then were fed limestone (9.87 g) to assess limestone solubilization.

Limestone was solubilized to a greater extent in hens that were fed low levels of P (0.3 or 0.4%) in the diet. Limestone solubilization was found to be inversely proportional to the amount fed. Changes in pH of the digestive tract were related to time during egg cycle. The pH of the digestive tract was generally low between 8 and 16 hours postoviposition, a period of active calcification. Vitamin D₃ did not influence limestone solubilization.

Key Words: In vivo limestone solubilization • phosphorus • vitamin D3 • plasma Ca • pH of digestive tract