Abstract
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 to maintain adequate egg production and available Ca blood level.
Highlights
Calcium is the mineral with the highest concentration in the body of poultry, consisting of 1.5% of its body weight
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 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
Summary
Calcium is the mineral with the highest concentration in the body of poultry, consisting of 1.5% of its body weight. Medullary bones in females are shaped in response to estrogen The role of these bones in mineral homestasis is more important than their structural skeletal function, and it is associated to bone mineralization and eggshell formation. Unbalanced diets may deeply influence the capacity of hens maintaining bone integrity during lay, as bones may be required to supply calcium for egg production and body maintenance, when hens are still growing. The study of different calcium levels fed at different combinations of particle size is essential in layers, as both these factors influence bone calcium content. The present experiment aimed at studying the effect of dietary calcium levels and limestone particle size composition on performance parameters, calcium absorption, and tibial calcium content of commercial layers in the beginning of the first laying cycle
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