Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science


Experiment one was a 3 x 3 x 2 factorial arrangement of three levels of calcium (Ca) (3.0, 3.5, and 4.0%) fed with three phosphorus (P) feeding programs to two strains of laying hens for 336 days. The P programs were .64% P fed continuously; .64, .54, and 44% P or .56, .49, and .39% P fed when hens were 24-36, 36-52, and 52-72 weeks of age, respectively. In addition to production traits, measurements of P retention were made at 34, 42, 50, 62, and 72 weeks of age and phytate P retention and % P associated with excreted phytate at 34, 50, and 72 weeks of age. The phase feeding P programs adequately supported production characteristics. Average total P retention was 104, 148, and 178 mg/day when hens were fed 3.0, 3.5, and 4.0% Ca, respectively. At 42 weeks of age, ambient temperature was relatively high and P retention decreased from 96 to 49 mg/day as dietary Ca increased from 3.0 to 4.0%. P feeding programs had no consistent effect on P retention in this experiment. Phytate P retention was high at 34 weeks of age, averaging 46.6% but declined to 9.1 and 16.5% at 50 and 72 weeks of age, respectively. Dietary Ca had an adverse effect on phytate P retention at 50 and 72 weeks; as Ca increased to 4.0%, phytate P retention decreased and the % P associated with excreted phytate increased;Experiment two involved feeding two levels of Ca (.8 and 1.2%) to one-week-old chicks for 7 days during which time ('33)P was administered to each chick. Serum P and excreta ('33)P activity were greater in chicks fed .8% Ca, while femur ('33)P was greater in chicks fed 1.2% Ca. The % P associated with excreted phytate ranged from 5.6 to 7.0% and phytate P utilization ranged from 31 to 48%. P retention and bone P deposition were greater in chicks fed 1.2% Ca;The final experiments were conducted utilizing isotope-dilution (('33)P) and comparative-balance methods to estimate urinary and fecal P excretions by laying hens fed 3.46 or 4.2% Ca. The injected ('33)P required 34-42 hours to stabilize in liver and kidney tissue. Increasing dietary Ca (3.46 vs. 4.2%) favorably affected egg production (91.9 vs. 96.6), femur bone ash (55.98 vs. 57.75%), P retention (17.9 vs. 135.0 mg/hen daily), and P balance (-74.0 vs. 38.4 mg/hen daily). Hens fed 3.46% Ca had increased P in excreta and the source of this was urinary P excretion. Endogenous P secreted in the intestinal tract constituted only 1% of the total P in ileal digesta and in excreta.



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Sheila Eipperle Scheideler



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129 pages