Estimation of calcium and phosphorus requirement in laying hens by balance techniques

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Abstract
Balance studies with Leghorn hens in good production were conducted to estimate their calcium and phosphorus requirement. The requirement, defined as the dietary level of calcium that maintained calcium equilibrium and optimum shell thickness, was found to be 3 g./hen/day. Percentage calcium retention (% retention) at high levels of calcium intake was a linear function of the reciprocal of calcium intake, the slope being equal to absolute calcium retention, but at levels below the requirement % retention increased at a decreasing rate. In the zone of calcium requirement % retention was 50‐55.Phosphorus excretion behaved as a linear function of phosphorus intake. The failure of the extrapolation method to estimate endogenous phosphorus excretion in the laying hen is discussed. Phosphorus requirement, defined by phosphorus equilibrium, was found to be between 0.24 and 0.36 g./hen/day.Measurements of plasma alkaline phosphatase and plasma inorganic phosphorus substantiated the respective requirements for calcium and phosphorus as determined by balance studies.