Plasma Phosphorus at 0, 6, and 21 Hours Postoviposition in Hens Laying in the Morning or Afternoon

Two experiments were conducted using White Leghorn hens. Blood samples were collected immediately following oviposition (0 hr) or 6 or 21 hr postoviposition from hens laying in the morning or afternoon. Plasma phosphorus was determined at each time period. In Experiment 1, plasma phosphorus at oviposition was essentially the same for hens laying in the morning or afternoon (3.95 and 4.10 mg/dl, respectively). At 6 hr postoviposition plasma phosphorus was lower than that observed at 0 hr (3.22 and 3.15 mg/dl, respectively). When comparing plasma phosphorus levels at 21 hr postoviposition of hens laying in the morning or afternoon a higher (P less than or equal to .05) phosphorus level was observed for hens that laid in the morning (5.90 vs. 4.91, respectively). In Experiment 2, plasma phosphorus levels at 0 and 6 hr postoviposition were 3.32 vs. 3.18 and 2.81 vs. 2.74 mg/dl for hens laying in the morning and afternoon, respectively. At 21 hr postoviposition, phosphorus values of 5.30 vs. 3.65 mg/dl were reported for hens laying in the morning and afternoon, respectively. Data also indicated that on the day a hen does not lay an egg, plasma phosphorus does not rise. An hypothesis is offered to explain the difference in egg shell quality between eggs laid in the morning or afternoon.