Re-evaluation of requirement of Calcium and available Phosphorus for starting meat-type chicks.

Abstract

Since availability of phosphorus in some of the important feed ingredients of plant origin, such as yellow corn and soybean meal was found to be almost negligible by the bioassay based on toe ash content, re-examination of requirement of phosphorus in Japanese Feeding Standard, which was shown as percent of total phosphorus, was required.In 3 experiments, total 720 one-day-old White Leghorn male chicks were fed diets containing graded levels of calcium from 0.6 to 1.8% and available phosphorus from 0.21 to 1.29% for 3 weeks. Growth responses and toe ash content were determined. By multiple regression analyses, quadratic equation1) to describe the responses of the chicks (y) against dietary levels of calcium (x1%) and available phosphorus (x2%) was obtained, and they=b0+b1x1+b2x2+b11x12+b22x22+b12x1x2…(1)equations were transformed into standard ellipsoidal equations. The response surfaces were given by contour lines. The square root of residual from regression, S, and the maximum response, y, among others were calculated. The responses within the contour line corresponding to ys-S were suspected to be optimum.Two response surfaces for body weight gain and feed intake were quite similar. High levels of dietary available phosphorus, particularly at low levels of calcium, decreased feed intake, resulting in depression of growth rate. This depression of feed intake and growth rate did not change feed efficiency (gain/feed).The maximum toe ash content was calculated to be 15.6%. The contour line corresponding to ys-S, which was 15.1%, indicated that the content will be obtained at the calcium levels over 0.95% and available phosphorus levels over 0.56%. A combination of 1.4% of calcium and 0.56% of available phosphorus was recommended to keep toe ash content of 3-week-old egg-type chicks over 15.1%. If toe ash content could be at least 14%, combinations of calcium and available phosphorus of 1.0-0.35 or 0.8-0.5 were selected to keep growth rate and feed intake maximum.