الفهرس 
Effect of low protein diets on performance of broiler chicks
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Abstract
Three experiments were carried out at the poultry production unit, Faculty of Agriculture, Ain Shams University, Shalakan, Qalyubia, Egypt, aimed to investigate the effect of Guanidino acetic acid (GAA) and or xylanase enzyme (xyl.) to maximum protein and metabolizable energy utilization in low protein and/or energy diets for broiler chicks. One thousand and eighty, one day old of male Hubard broiler chicks, randomly distributed over 18 treatments within three experiments. Each treatment comprised of 60 chicks divided into 6 replicates of 10 chicks each. The control group was considered twice within three different experiments. Parameters measured were performance, carcass characteristics and some plasma constituents.
In the first experiment: Results indicate that Feeding broiler chicks diets supplemented with 600 g/ton or 1200 g/ton GAA showed a significant increase in BWG by 4.60 and 3.96% compared with those fed 0.0% GAA diets, Significant differences in feed conversion ratio between broiler chicks fed standard diets and low CP (-2%) diets in starter (1.32 vs 1.46), grower (1.53 vs 1.57) and whole period (1.62 vs- 1.68). The best FCR and PCR during whole experimental period (0-5 weeks) was detected for the chicks fed diets supplemented with GAA (1.62 for both 0.06 or 0.12%). However, the best energy conversion ratio (ECR) was recorded with chicks fed (0.12% GAA, 5.17) diets compared with those fed (0.06% GAA, 5.20) diets. Addition of GAA (0.0, 0.06 and 0.12%) had no significant effects on most of blood parameters and carcass characteristics .
In the second experiment: During whole experimental period (0-5 wks), the chickens fed standard diets gained significantly more than those fed low energy diets (-150 Kcal/kg), being (2069.13 vs 2003.509). There were significant differences (P<0.01) in LBW values due to different broiler chicks fed diets supplemented with GAA, Xyl or GAA + Xyl compared to those fed unsupplemented diets. The best FCR was observed
for chickens that fed (GAA+Xyl.) diets (1.58) followed by those fed on (Xyl.) diets or (GAA) diets (1.61), while those fed on unsupplemented diets were the worst (1.68) during the whole experimental period and differences among treatments were significant. No significant differences were observed in most of studied traits (i.e. carcass, giblets, total edible parts and abdominal fat) among chickens fed diets with or without different feed additives. Neither dietary ME nor feed additives had a significant effects on most blood plasma parameters.
The third experiment Chicks fed standard diets recorded significantly higher LBW and BWG compared with those fed low (ME and CP) diets, being (2108 vs 1907 and 2069 vs 1868) respectively. There were significant differences (P<0.01) in FCR among different levels of ME and CP or different feed additives during starter, grower, finisher and whole experiments periods. Carcass percentage was significantly increased by 2.60 and 4.57% for broiler chickens fed diets supplemented with GAA and GAA + Xyl, respectively as compared to those fed the standard diets (64.53%). There were insignificant differences in villi height, villi width and crypt depth among treatments chickens fed low energy and protein diets.
Key words: Guanidino acetic acid (GAA), Xylanase enzyme (xyl.), metabolizable energy, Amino acid