The phosphorus excretion pattern and balance during one egg cycle of the laying hen fed a phosphorus deficient diet with or without a single dose of phosphoric acid.

A balance trial was conducted to study the phosphorus excretion pattern of laying hens in relation to egg cycle. Excreta were collected quantitatively at 4, 8, 12, and 24 hr after oviposition. The amount of feed consumed corresponding to the excreta collected at a specific time interval was calculated using chromic oxide as a marker. The percent recovery of chromic oxide with laying hens was 73.97 +/- .56%. The maximum apparent digestibility of the dietary phosphorus, all of plant origin, was estimated to be 28.9 +/- 3.1% during 0 to 4 hr after oviposition when the endogenous excretion of phosphorus was theoretically minimized. Laying hens fed a diet containing .30% phosphorus excreted 24.3 mg less phosphorus than intake during the day, indicating that hens had to withdraw approximately 100 mg of phosphorus from their body to produce an egg. These hens excreted 63.1 +/- 27.0 mg of endogenous phosphorus during the 24 hr period, most of which was excreted during the period between 12 to 24 hr after oviposition of the previous egg. The excretion pattern of phosphorus was closely related to the egg laying cycle of the hen. Hens dosed with 100 mg of phosphorus, as a phosphoric acid solution, excreted more phosphorus than the undosed control birds. Approximately 45 mg of 100 mg of the phosphorus dose were excreted during the 24 hr period. At least 84.8 mg of the dosed phosphorus were absorbed within 12 hr and a part of it was excreted during the later period. Data indicated that the true absorption rate of the dosed phosphorus might have been much faster.