The present study was carried out to evaluate the response of broiler
chickens fed diets with different crude protein levels to dietary enzyme (Allzyme
Vegpro) supplementation. Day-old unsexed broiler chicks were fed on a commercia!
starter diet (contained 22% crude protein and metabolizable energy, ME, 'of about
3100 kcal/kg) up to 17 days of age. Then, two hundred and fifty-two birds were
randomly distributed into six equal experimental groups, each with six equal replicate
groups, kept at the rearing batteries and fed ad libitum their respectiye mash
experimental diets. Six iso-energetic diets (ME of about 3000 kcallkg) contai~ed three
levels of crude protein (20,18 or 16%) and two levels of enzyme supplement~tion (0.0
or 1.5 g/kg diet) were formulated and used from 17 to 45 days of age. The ~riteria of
response were live body weight, daily weight gain, feed intake, protein intake and feed
conversion. Total mortality and economic efficiency of feeding were also determined.
Nutrient digestbilities of the experimental diets were measured when the birds were 5
weeks of age. At the termination of the study, certain parameters of carcass traits and
some blood constituents (plasma levels of glucose, total protein, total lipids and
cholesterol as well as activities of plasma transaminases: AST and AL T) were
quantified. The results obtained, for the whole experimental period, can be
summarized as follows: Regardless of enzyme supplementation, decreasing dietary crude protein
(CP) level from 20 to 16% adversely affected (P$0.01) live body weight, body weight
gain, daily protein intake, feed conversion ratio and economic efficiency of feeding.
Also, decreasing dietary CP level significantly (P$0.01) increased abdominal fat
percentage. However, dietary CP level had no significant effects on mortality of
chicks, daily feed intake, nutrient digestibility, tested blood parameters or carcass
traits. Enzyme supplementation, regardless of dietary CP level, significantly improved
(P$0.01) the feed conversion ratio of broiler chicks during the whole period of study.
All other criteria measured were not significantly (P>0.05) influenced by the enzyme
supplementation. Also, the interactions between dietary CP level and enzyme
supplementation were not significant (P>0.05) for all studied criteria. Under the
conditions of this study, economically, it was concluded that a level of 20% CP with or
without enzyme supplementation is the optimal dietary protein level in grower broiler
diets for maximizing broiler growth performance and optimizing the efficiency of feed
utilization. The diet should also be well balanced in all nutrients and its CF' content
should provide a balanced pattern of amino acids.