Requirement of phosphorus of meat type chicks in Japanese Feeding Standard, which was shown as 0.6% of total phosphorus, was re-examined to show as percent of available phosphorus.
In 3 experiments, total 810 one-day-old meat-type chicks of both sexes 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 was determined. By multiple regression analysis, quadratic equation (1) to describe the responses of the chicks (y) against dietary levels of calcium (x₁%) and available phosphorus (x₂%) was obtained, and
y=b₀+b₁x₁+b₂x₂+b₁₁x₁²+b₂₂x₂²+b₁₂x₁x₂…(1)
the 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_S, among others were calculated. The responses within the contour line corresponding to y_s-S were suspected to be optimum.
Three response surfaces for body weight gain, feed intake, and feed efficiency were quite similar. The response surfaces for the initial two responses of meat-type chicks were quite agreeable to those of egg-type chicks. High level of dietary available phosphorus decreased feed intake, resulting in depression of growth rate.
No significant sex difference was observed in toe ash content. Significant breed difference was observed in response patterns of toe ash between meat-type and egg-type chicks.
The maximum toe ash content of meat-type chicks was calculated to be 14.6%, which was significantly lower than that of egg-type chicks of 15.6%. From the contour line corresponding to y_s-S, a combination of 1.3% of calcium and 0.75% of available phosphorus was recommended to keep toe ash content of 3-week-old meet-type chicks over 14.1%.