The present study was performed to investigate the effects of feeding low-
Ca-P·diets. supplemented with microbial phytase and vitamin D3. on productive
performance. eg9 quality, eg9 fertility and hatchability, and some blood constituents of
Gimmizah laying hens. Three hundred and thirty. 28·week-old birds were randomly
distributed into ten equal groups; each group was divided into 3 replications of 11
birds each (ten females and one male) and housed in floor pens. All birds were kept
under the same managerial conditions and fed their respective experimental diets
from 28 up to 48 weeks of age. Ten isoenergetic (metabolizable energy of about 2770
kcallkg)-isonitrogenous (crude protein of about 16.35%) experimental diets were
prepared and used. The control diet (Diet 1) was formulated to contain 3.28% Ca and
0.42% available P (AP). Diet 2 (served as a negative control) was the same as the
control diet (Diel 1.) but had only 75% and 50% of the Ca and AP contents of the
control diet, respectively. The remaining eight diets were obtained by supplementing
the negative control diet (Diet 2) with two microbial phytase (MP) levels (500 or 1000
Ulkg; Diets 3 and 4, respectively). two vitamin 03 (VO) levels (400 or 800 lUlkg; Diets
5 and 6, respectively), or with different combinations of MP and VD (500 U MP+400 IU
VD. 500 U MP+800 IU VO, 1000 U MP+400 IU VD or 1000 U MP+800 IU VDlkg diet;
Diets 7. 8, 9 and 10. respectively). Records on body weight. daily feed intake, egg
production rate (EPR). egg weight (EW), daily egg mass (OEM) and feed conversion
ratio (FCR; 9 feed: 9 egg) were maintained. A series of egg quality tests were made at
four-week intervals. Egg fertility. hatchablity (% of total eggs) and total embryonic
mortality, and egg-weight-loss (%) of hatching eggs were evaluated. At the end of
study. some blood plasma parameters (total protein, albumin (A), glubulin (G). NG
ratio, Ca, inorganic P, and activities of Iransaminases: AL T and ASl1 and tibia bone
length and width, and its Ca and P contents were determined. The results obtained
can be summarized as follows: Birds fed on Diet 2 (negative control diet; NCO) performed less, but significantly
similar to those fed on Diet 1 (control) for EPR, OEM and FCR. On the other hand,
birds fed on NCO with supplemental MP, VD or their combinations (Diets 3 to 10)
Significantly surpassed those of either control or negative control in EPR and OEM
with a concomitant improvement in FCR. Feeding the negative control diet (NCD) adversely affected eggshell quality (shape
index. relative shell weight and shell thickness), interior quality (yolk index and
Haugh units), egg fertility, eggshell and tibia Ca contents and plasma concentrations
of TP, Ca. and inorganic P compared with the control diet, all other measurements
were not affected. Supplementing the NCO with MP alone. particularely with the high level of MP (1000
UII EPR, DEM and FCR, and also attained significant improvements in relative yolk
weight. yolk index, I-'augh units and tibia P content. compared with the control diet.