Abstract
To evaluate the effect of different levels of citric acid (CA) combined with phytase and calcium levels in the diets of laying hens on the calcium and phosphorus (P) contents of eggs: yolk-albumen and shell, yolk color and egg quality. A study was conducted with 24-week-old laying hens fed with a diet based on sorghum and soybean meal with 2.7 Mcal of EM/kg, 15% crude protein, 3.25% calcium and 0.25% available P. The levels of CA, phytase and calcium were 0%, 0.6% and 1.2%; 0 and 300 units of phytase (PHYU)/kg; and 3.0% and 3.25%, respectively. Phytase was added as an ingredient into to the diets, contributing 0.1% P and 0.3% calcium. A completely randomized factorial experiment was performed with a 3 × 2 × 2 design and 4 replications. The CA increased (P < 0.05) the P in the shell, and the combination of 1.2% CA, 300 PHYU phytase and 3.25% calcium increased (P < 0.05) the calcium in the eggshell. There was a CA × phytase × calcium interaction (P < 0.05) affecting egg yolk pigmentation; there were no differences in egg quality. It was concluded that adding CA to the diets of laying hens increases eggshell calcium content, and improves the phytase response. 1.2% CA × Phytase × 3.25% calcium significantly increases shell calcium by 0.56 g. Under the conditions of the present investigation, it would imply greater resistance of the eggs to be broken in the handling from the farm to the sales centers and consumer. Phytase interacts negatively with 0.6% CA at low calcium levels to degrade the yellow pigmentation of the yolk.
Highlights
The phytic acid present in vegetable seeds reduces the availability of phosphorus (P) and, at a certain pH interferes with the dispensability of minerals [1], which are excreted into the environment
Phytase interacts negatively with 0.6% citric acid (CA) at low calcium levels to degrade the yellow pigmentation of the yolk
Studies show that citric acid (CA) reduces the chelation potential of phytic acid by binding to certain minerals, which results in lower excretion and greater availability of P, calcium and nitrogen [7]-[13]
Summary
The phytic acid (myoinositol hexaphosphate) present in vegetable seeds reduces the availability of phosphorus (P) and, at a certain pH interferes with the dispensability of minerals [1], which are excreted into the environment. Studies show that citric acid (CA) reduces the chelation potential of phytic acid by binding to certain minerals, which results in lower excretion and greater availability of P, calcium and nitrogen [7]-[13]. High levels of calcium and a neutral pH allow calcium to bind to phytic acid and form calcium phytate salt, an insoluble compound, which makes calcium unavailable to laying hens and as well as inaccessible to phytase [14]. In a study of the effects of CA combined with phytase excretion and availability of calcium and P in the diets of molting laying hens, it is concluded that 2% CA increases the content of calcium in the shell and P in the yolk-albumen of the egg, and reduces N excretion; and 2% CA combined with 600 phytase units (PHYU) reduces P excretion and increases egg weight [9]. The above led to the proposed study with the following objectives: 1) evaluate the effect of CA on the calcium and P content of the egg including the yolk-albumen and shell, pigmentation of the yolk and the quality of the egg; 2) evaluate the effect of CA on the phytase response in diets of laying hens from the ages of 24 to 39 weeks; 3) evaluate the effects of the diets on egg calcium and P contents in the yolk-albumen, shell, pigmentation of the yolk and egg quality in laying hens aged 24 to 39 weeks
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