Cyclic changes in serum phosphorus of laying hens.

Three trials were conducted to measure changes in the serum phosphorus level of laying hens over a 24-hour period. Sixty-three-week-old hens were selected for blood sampling according to the criteria that: 1. they laid an egg the day prior to and the day of blood collection and 2. the oviposition time on both days was 10 a.m. +/- 2 hours. Blood samples were obtained via heart puncture. Serum was collected by centrifugation, deproteinized and analyzed colorimetrically for phosphorus content. Sampling times were as follows: Trial 1--6 p.m., 12 midnight, 6 a.m. and 12 noon; Trial 2--6 a.m., 8 a.m., 10 a.m., 12 noon, 2 p.m., 4 p.m. and 6 p.m.; Trial 3--12 midnight, 4 a.m. and 7 a.m. Hens used in this study received natural and/or artifical light from 4:30 a.m. to 7:30 p.m. each day. Results indicated that serum phosphorus reached a peak of 6.08 mg.% at 7 a.m. At 8 a.m., the phosphorus level dropped to 4.88 mg.% and remained within 0.08 mg.% of this value until 12 noon. From 2 p.m. to 6 a.m. it gradually increased from 5.29 mg9% to 5.80 mg.%. Observed changes in serum phosphorus over time are related to changes in shell calcification, bone resorption and remineralization, and renal clearance.