Effects of Calcium and Phosphorus Levels on Egg Weight and Egg Shell Quality in Laying Hens

Abstract

Fourteen hundred caged Leghorn hens were fed 10 dietary treatments formulated at three constant calcium levels, 2.75, 3.75, and 4.75%, and two variable levels, decreasing from 3.75 to 2.75% and increasing from 3.75 to 4.75%, each in .25% steps each 8 wks, with each calcium treatment fed at two phosphorus levels, .35 and .45% available or .56 and .65% total, from 28 weeks to 64 weeks of age. Egg weight was highly significant and inversely related to the dietary calcium level; 1% additional calcium depressed egg weight approximately .4 g. Egg shell weight, shell weight per unit surface area (SWUSA), and specific gravity were highly significantly related to dietary calcium level. SWUSA and specific gravity were significantly inversely related to the phosphorus level. Increases of 1% dietary calcium increased shell weight approximately .05 g, SWUSA 1.25 mg, and specific gravity .0013. Egg production and feed efficiency were not significantly affected by any treatment. It appears feasible to lower calcium levels during the early months of production to maximize early egg weight and then increase the calcium levels as the hen ages to maximize shell quality by increasing shell weight while limiting egg weight increase. Excess dietary phosphorus should be avoided for highest shell quality.