A 3 x 3 faclorial experiment was conducted to determine the enects of difierenl
available phosphorus (AP) I eveis In cliets of Marnourah laying hens with or without
dietary microbial phytase (MP) supplementation on productive performance (egg
production rate, egg weight. egg mess and feed conversion), egg quality ( some
exterior and interior parameters end Ca and P contents of egg shell ), and some blood
constituents (levels of ptasma total protein. albumin and globulin, and activities of the
transaminase enzymes: GOT and GPI ). Tibia bona length and wIdth and its content
of Ca and P were also determined. Three isccatoric (ME or about 2760 kcat/f:Q)-
isonitrogenous (CP of about 16 %) diets, containing AP revels of 0.405, 0.269 or O. t 35
~~ were formulalethree levels of supplemental MP (0. 500 or 1000 Ulkg die!),
All birds had a free access 10 feed and water throughoul the experiment.al ~riod from
JO to 50 weeks of age. The obtaioed results can be summarized as (ollows: 1- Regardless of MP supplementation, re 0.135% caused a sigf'lificanllncrease in (eed InL:lke wilh concornitanlry less eHicif:nl
feed conversion, and signifICant reductions In eggshell weight and lhicknes s. obis
bone width, and P content of ~gshell, but Increased the activities ot plasma
transarninases ( GOT and GPT ). In addition, egg production of the layers was
deaeased: but oct signil1canUy, with reduci"9 dietary AP level. 2· lndependently of the eHect of dietary AP level, the dietary supplernentatoo with MP
resulted In significanl improvements in egg production rate. egg weight, egg mass,
feed conversion, and eQgshell weight and thickness, as well as significant increases
in tibia length and Ca content of the eggshell. Concentrations of total protein.
albumin. Ca and P in the plasrna or layers were signlficanlly increased. whereas
activities of GOT and GPT were reduced In response 10 dielary MP
supplementation. J. There were significant ioreracuons between the eHecls of dielarv liP and
supplemental MP levels on most of the estimated parameters. It can be concluded that supplementation of laying hen diets: In particular tnose
conraininq low available phosphorus. with microbial pbytase at a supplementary level
of 500 U/kg diet. may improve the performance of laying hens lor egg production and
leed convsrslon. with no detrimental eHect on egg Quality.