Egg-shell deposition and blood plasma inorganic phosphorus concentration in individual laying hens

1. The relationship between plasma inorganic phosphorus measured at the end of the dark period and the weight of the next egg shell produced was investigated in 30 Hisex Brown hens. 2. Hens received an adequate conventional layers' diet and the lighting pattern was conventional (17 L: 7 D). Observations were made early (31 to 40 weeks) and late (62 to 68 weeks of age) in the laying period. 3. Eggs were classified by position in the clutch sequence and significant negative correlations were found between shell weights of early eggs in the sequence and plasma phosphate at the end of the dark period. 4. No significant trends were found in plasma total calcium. 5. No significant differences were found in bone compositions of birds producing consistently more or less than average shell weight during the laying period. 6. The negative correlations between plasma phosphate and shell weight are consistent with the observations of Sauveur and Mongin (1983) and show that impairment of shell deposition is associated with skeletal mobilisation as indicated by increase in plasma phosphate. This is consistent with the observations on bone composition and indicates that selection for shell quality will tend to select birds which are not dependent on excessive skeletal mobilisation during shell formation.