Abstract
The experiment was conducted to determine the nutritional requirement of calcium and the best calcium:available phosphorus ratio for commercial layers at the post-laying peak. A total of 324 Hy-Line W-36 laying hens were utilized in the period from 42 to 58 weeks of age, distributed in a completely randomized design in a 3 × 3 factorial arrangement, composed of three levels of calcium (39, 42 and 45 g/kg) and three calcium:phosphorus ratios (12.12:1; 10.53:1; and 9.30:1), totaling nine treatments with six replications and six birds per experimental unit. There was no significant effect from the calcium levels × calcium:phosphorus ratio interaction for any of the variables studied. The calcium levels and the calcium:phosphorus ratios did not affect the variables performance or egg and bone quality. At the evaluation of the calcium:phosphorus balance, as the levels of calcium of the diet were raised, the intake of calcium and phosphorus and the contents of mineral matter and calcium in the excreta increased linearly, and the retention of calcium by birds decreased linearly. With the reduction of the calcium:phosphorus ratios of the diet, intake, retention and excretion of phosphorus by layers increased. Diets containing calcium at 39 g/kg and a calcium:phosphorus ratio of 12.12:1, corresponding to an increase in calcium of 3.51 g/bird/day and available phosphorus of 289 mg/bird/day, meet the requirements of calcium and available phosphorus of white egg layers in the period from 42 to 58 weeks of age.
Highlights
Over the years, commercial layer strains have been genetically improved in order to be more productive
The results obtained for the productive performance parameters of the layers in function of the calcium levels in the diets are in line with those found by El-Ghamry et al (2011), who evaluated four levels of calcium between 24 and 33 g/kg for Fayoumi laying hens in the period from 45 to 57 weeks of age and did not verify difference in egg production, egg weight and egg mass
Different result was observed by Murata et al (2009), who recorded greater egg production at the estimated calcium level of 40.5 g/kg and linear effect for egg weight and feed conversion per egg dozen of white egg layers fed diets with calcium levels of 37.5; 41.5; or 45.5 g/kg
Summary
Commercial layer strains have been genetically improved in order to be more productive. These advancements make them more demanding as for nutrition. Recurring studies are necessary for the update of the nutritional requirements, for these birds to express their maximum production potential. Because the requirements of calcium and phosphorus of layers have constantly changed, special attention has been drawn to research on the requirements of these minerals for laying birds. Calcium and phosphorus are considered the main minerals in diets for layers, due to their expressive participation in the metabolism and in the quality of the eggshell. While calcium is necessary at big quantities, phosphorus is the mineral that most encumbers the final cost of diets, even though it is required at low amounts
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