A total of 405 23-week-old ISA® Brown layers were distributed in a
completely randomized experimental design in a factorial arrangement
with nine treatments consisting of three dietary calcium levels (3.5,
3.75, and 4.5%) and three limestone particle sizes (100% fine
limestone (FL), 70% FL + 30% coarse limestone (CL) and 50% (FL) +
50% (CL)), with nine replicates of five birds per cage. The following
parameters were evaluated: percentage of lay, defective eggs, egg
weight, egg mass, feed intake, feed conversion ratio (per kg eggs and
per dozen eggs), and mortality. Dietary Ca levels significantly affected
lay, with birds fed diets containing 4.5% calcium producing less eggs
as compared to those fed 3.0 and 3.75% Ca. Egg production linearly
decreased as dietary Ca levels increased, but blood Ca levels (mg/L)
increased in 28-week-old birds. The interaction of dietary Ca levels and
limestone particle sizes resulted in a reduction in tibial ash Ca content
as dietary Ca levels increased and as fine limestone was replaced by
coarse limestone. It is concluded that a dietary Ca level of 3.75% and
100% fine particle limestone are required