Effects of inositol, inositol-generating phytase B applied alone, and in combination with 6-phytase A to phosphorus-deficient diets on laying performance, eggshell quality, yolk cholesterol, and fatty acid deposition in laying hens.

Phytase B, a product of Aspergillus niger phyB gene expressed in Trichoderma reesei, which increased myo-inositol concentrations in 20 mM sodium phytate solution 7.5-fold during 120-min incubation, a combination of phytase B with 6-phytase A, and pure myo-inositol were tested as feed supplements in Bovans Brown laying hens. In the 2-factorial experiment (2×5), birds from wk 50 to 62 were fed 2 basal diets, corn-soybean (CSM) or wheat-soybean (WSM), using 12 one-hen cages per treatment. For both basal diets, the dietary treatments included negative control (0.08% nonphytate P in CSM, 0.13% nonphytate P in WSM; NC); internal control groups, NC+0.04% nonphytate P from monocalcium phosphate, MCP (IC); NC+0.1% of myo-inositol (Inos), NC+phytase B at 1,300 units of phytase B-acid phosphatase activity (AcPU)/kg (PhyB), NC+phytase B at 1,300 AcPU/kg+6-phytase A at 300 FTU/kg (PhyA+B). Feed intake, laying performance, and eggshell quality were determined. The total lipid and cholesterol contents as well as fatty acid profile were assessed in egg yolks collected from hens fed CSM diets, as was fatty acid profile. The hens fed the WSM diet consumed significantly more feed, laid a higher mass of eggs daily with higher mean weights, and had a higher hen-day egg production than the birds receiving the CSM diets. Similarly, higher values for yolk weights, shell weights, shell thickness, shell density, and breaking strengths were determined in the eggs laid by the hens fed the WSM diets. In hens fed either the CSM diets with phytase B alone, or in combination with 6-phytase A, enhanced feed intakes, egg mass, and hen-day egg production were recorded. Phytases also enhanced the eggshell quality parameters in the hens fed both variants of the diets. Phytase B alone, or in combination with 6-phytase A, reduced the total lipid and cholesterol concentrations in egg yolks collected from the hens fed the CSM diets, whereas the combination of both phytases improved the n-6:n-3 polyunsaturated fatty acids ratio. In the CSM diets, the supplemental myo-inositol suppressed feed intakes, reduced egg production, had no effect on eggshell quality and reduced the deposition of eicosanoid fatty acids in yolks. When comparing the effects of feeding MCP, myo-inositol, and phytases on the nutritional quality of the eggs laid by the hens fed phosphorus-deficient CSM diets, it seems that the enhancements in nutritional quality cannot be attributed solely to higher phosphorus level or higher concentrations of myo-inositol.