Two experiments were conducted to determine the effect of dietary energy, protein, and fat during the latter parts of the growing period and the early parts of the laying cycle on early egg weight and egg components. In Experiment 1, pullets were fed diets containing two levels of energy (2,816 and 3,036 kcal ME/kg), two levels of protein (14 and 18%), and two levels of fat (0 and 4%) in factorial arrangement from 14 to 18 wk of age. From 18 to 34 wk of age, pullets from all of the growing regimens were fed a 16.5% protein diet. In Experiment 2 (18 to 34 wk of age), six diets were used. The energy, supplemental fat, and protein content of the diets were: T1:2,816 kcal/kg, 0%, 17%; T2:2,816 kcal/kg, 0%, 21%; T3:2,816 kcal/kg, 4%, 17%; T4:2,816 kcal/kg, 4%, 21%; T5:3,036 kcal/kg, 4%, 17%; and T6:3,036 kcal/kg, 4%, and 21%. The data were analyzed factorially with energy constant and fat and protein variable (T1 to T4) and with fat constant and energy and protein variable (T3 to T6). In Experiment 1, 18-wk body weight increased slightly (P < .05) due to increasing the energy or adding fat to the diets, whereas egg weight during the early stages of egg production was increased modestly (P < .05) only due to increasing the energy level. In Experiment 2, when energy was constant, egg weight was increased due to increasing the protein level or adding fat to the diets (P < .05). When fat was constant, egg weight was increased only due to increasing the protein level (P < .05). The increased egg weight under these conditions was due mainly to increasing the albumen weight. The results indicated that egg weight during the early stages of the egg production cycle can be increased due to increasing the protein level from 17 to 21% or by adding 4% fat to the conventional layer diets, and that the beneficial effect of fat on egg weight is independent from its energy effect.

A 4 x 7 factorial experiment was conducted to determine the effect of different nonphytate phosphorus (NPP) regimens with and without phytase on performance of four strains of laying hens. The strains used were Babcock B300, DeKalb Delta White, Hy-Line W36, and ISA-White. The birds of T1 (Treatment 1), control diet, were fed a diet with 0.45% NPP for the entire experiment (20 to 63 wk of age). The birds of T2 were fed a NPP regimen of 0.25% for Phase 1 (20 to 35 wk of age), 0.2% for Phase 2 (36 to 51 wk of age), and 0.15% for Phase 3 (52 to 63 wk of age). The birds of T3 and T4 were fed a NPP regimen similar to T2 plus 150 or 300 units phytase/kg diet, respectively. The birds of T5 were fed a NPP regimen of 0.2, 0.1, and 0.1% for Phases 1, 2, and 3, respectively. The birds on T6 and T7 were fed a NPP regimen similar to T5, with 150 and 300 units phytase/kg diet, respectively. The criteria for evaluating the effect of dietary treatments were production performance, shell quality, bone ash, and total P excretion. Production traits were drastically reduced and mortality was drastically increased when the birds of T5 were fed a diet with 0.1% NPP during Phase 2 (36 to 51 wk of age). Increasing the NPP level of this treatment from 0.1 to 0.45% during Phase 3 restored the production traits almost to the control level during this phase of the experiment. The NPP regimen of 0.2-0.1-0.1% plus either level of phytase (T6 and T7) restored most of the traits for the entire experiment to the control level (T1), except egg production (EP) and the nonprolapse mortality. Bone ash also remained significantly lower than the control group with this NPP regimen plus the higher level of phytase (T7). Production traits were reduced, and nonprolapse mortality was increased due to the use of a NPP regimen of 0.25-0.2-0.15% without phytase (T2) for the entire experiment. The NPP regimen of 0.25-0.2-0.15% plus the lower level of phytase (T3) restored all the traits except EP to the control level for the entire experiment. The only treatment that maintained performance of all the strains comparable to their controls for the entire experiment was a NPP regimen of 0.25-0.2-0.15% plus the higher level of phytase (T4). Total P excretion of birds fed this NPP regimen was reduced by 55.6% as compared to the control group. The data generally indicated that the higher level of phytase was more effective than the lower level in restoring the performance of birds fed the low-P diets to the control level. Numerous interactions existed among strain x diet for various traits throughout the experiment, indicating the NPP requirement for maintaining production performance may be different among strains.

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Two experiments were conducted to determine whether, by using a low-protein, amino acid-supplemented diet or a low-protein, amino acid-supplemented diet in conjunction with low-P, phytase-supplemented diet, the excretion of N and P could be reduced without affecting the productive performance of laying hens. Eight dietary treatments were assigned to Babcock B300 hens in each of 2 experiments that involved a positive control (16 to 16.5% CP) and a negative control (13% CP) with and without supplementation with the limiting essential amino acids. In experiment 1, supplementing the negative control with lysine, methionine, and tryptophan resulted in performance comparable to that obtained with the positive control, with the exception that egg weight was heavier for the negative control supplemented with amino acids. Supplementing the negative control with additional essential amino acids improved the performance higher than the positive control indicating that the positive control was deficient in one or more essential amino acids. In experiment 2, supplementing the negative control containing 0.2% nonphytate P (NPP) with all the limiting amino acids plus phytase resulted in performance comparable to the positive control group, which was fed 0.4% NPP without phytase. The results of a digestibility assay indicated that daily total P and N excretions of the negative control containing 0.2% NPP and supplemented with limiting amino acids and phytase were reduced by 48 and 45% of the positive control group, respectively, without compromising laying performance.

Two experiments were conducted to determine whether the presence of 25-OH-cholecalciferol (25-OH-D3) as compared to vitamin D3 produces any beneficial effect on shell quality of laying hens. Experiment 1 consisted of a 4 x 2 factorial arrangement of the treatments with four determined Ca levels (3.34, 4.3, 4.73, and 4.94%) and two sources of vitamin D (vitamin D3 and 25-OH-D3, which were used at 69 microg/kg diet or 2,760 IU/kg diet). Experiment 2 consisted of a 3 x 2 x 2 factorial arrangement of the treatments with three determined levels of nonphytate P (NPP) (0.11, 0.21, and 0.41%), two levels of phytase (0 and 300 U/kg diet), and two sources of vitamin D (vitamin D3 and 25-OH-D3, which were used at 69 microg/kg diet, the equivalent of 2,760 IU/kg diet). Substitution of vitamin D3 with 25-OH-D3 in neither of the experiments produced any beneficial effect on shell quality. A Ca level of 3.34%, which provided the birds with 3.63 g Ca/hen per d, was adequate for performance and eggshell quality. The NPP level of 0.11% was not sufficient to support performance. However, a NPP level of 0.21% was adequate and resulted in performance that was comparable to that of birds fed the 0.41% NPP diet. The presence of phytase did not have an effect on performance but reduced several indices of the shell quality. In conclusion, under the conditions of the current experiments, the use of 25-OH-D3 did not provide any advantage for shell quality or production performance.