الفهرس 
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Abstract
Summary and Conclusion : The main objectives of this work were to investigate : 1- The current study was carried out to determine the effect of feeding low-protein diets enriched with lysine plus methionine (LM), citric acid (CA) or their combination on laying performance, reproductive performance, egg quality, serum biochemical parameters and economic efficiency of Sinai laying hens from 30 to 46 weeks of age. 2- To assess the influences on neonatal immune response and growth performance of chicks hatched from those breeders fed the dietary treatments. To achieve these aims, a total of 210 Sinai pullets and 21 cockerels of the same breed at 30 weeks of age were housed on deep litter in floor pens (ten ♀: one ♂ per pen) and kept in an open-sided building. The dimensions of each floor pen were 200 cm length and 150 cm width. The birds were randomly assigned into seven dietary treatments, each with three equal replications. At the onset of the experiment, birds were weighed and assigned to treatments based on approximately similar live body weights in all treatments. The laying house used herein was naturally ventilated and all birds were exposed to a daily photoperiod of 16 hr. Sinai chickens were provided their test diets and fresh water ad libitum throughout the duration of this study, from 30 to 46 weeks of age. In an early study, Hussein et. al, (2010) estimated that the metabolizable energy (ME) and crude protein (CP) requirements of Sinai chickens were 2800 kcal ME per kg diet and 15% CP during the laying period in order to attain optimal performance. Such estimated requirements of ME and CP were used as a guide when calculating the nutrient contents of the test diets. Seven iso-energetic test diets were prepared and used. These diets were as follows: A basal diet was formulated to contain 15% CP to serve as a control diet while diets 2 and 3 contained 14 and 13% CP, respectively, but having the same lysine and methionine contents as those of the control diet. Diets 4 and 5 were compounded to contain 14 and 13% CP, respectively, but enriched with 0.2% CA without LM while diets 6 and 7 contained 14 and 13% CP, respectively, but fortified with CA and lysine plus methionine (LM). Ingredient composition and calculated analyses of the test diets are given in Table 4 (NRC, 1994). characteristics investigated included : Live body weight; egg production traits (egg number, average egg weight, egg mass); feed consumption; feed conversion, egg quality parameters; egg-yolk serum biochemical estimates; reproductive traits (fertility %, hatchability % and body weight at hatch); and the performance and neonatal immunity of chicks hatched from eggs of treated hens with dietary treatments. 1. Regarding body weight, hens fed the diet containing 13% CP supplemented with CA had significantly lower (P≤0.05) mean of change in body weight than that of the control group while other dietary treatments did not differ from the of the control group. 2. The hens fed diet 14% CP with LM+CA achieved satisfactory egg number/hen and returned to occupy the first position with respect to egg number as compared to the control diet by about 1.84 %. 3. Also, it must be mentioned that all dietary treatments did not significantly differ from the control group in trait of egg number except for the diet contained 13% CP with LM where this treatment led to a significant decrease in egg number/hen compared to the control diet. 4. No significant differences in egg mass were observed during the collective period, however, the diet contained 13% with LM or CA alone resulted in a significant decrease in egg mass compared to the control diet. 5. In comparison with the control diet, results obtained clearly indicated that the all dietary experimental groups consumed significantly higher amounts of feed than control group with exception those fed the diet contained 14% CP with mixture between EAA and CA. 6. Yolk index, Haugh units, percent yolk weight (YW) and percent albumen weight were not significantly affected (P>0.05) by dietary treatments. 7. It was noted that egg weight of hens fed the diet containing 13% CP enriched with CA was significantly lower (P≤0.05) than that of their control counterparts while egg weights of other experimental groups were insignificantly different from that of the control group. 8. Hens fed the diet containing 13% CP supplemented with LM plus CA achieved significantly higher (P≤0.05) egg shape index than did those fed the 13% CP with adding LM alone, but other experimental groups did not differ from the control group in their egg shell index. 9. Egg shell thickness of hens fed 14% CP-diet fortified with LM plus CA was significantly higher (P≤0.05) those of hens 14% CP-diets with or without CA alone. 10. The per cent egg shell weight of hens fed 13% CP-diet enriched with LM plus CA was significantly higher (P≤0.05) than that of hens given 13% CP-diet with CA alone. 11. Egg shell calcium% of hens received 13% CP-diets with or without CA and 14% CP-diet fortified with LM plus CA were significantly higher (P≤0.05) than that of the control group. 12. Egg shell phosphorus % of hens received 14% CP-diet fortified with LM plus CA was significantly higher (P≤0.05) than those of other dietary treatments. 13. Dietary treatments did not significantly (P>0.05) have any adverse effect on egg fertility, fertile hatchability or total hatchability. 14. It was interesting to note that means of hatchability of fertile eggs produced by hens fed the diets containing 13 or 14% CP with LM, CA alone or LM plus CA together exhibited slightly higher (P>0.05) means of means of hatchability of fertile eggs than did their control counterparts. 15. Concerning chick weight at hatch, hens fed the 14% CP diet enriched with CA produced significantly heavier chicks (P≤0.05) than those of hens fed the 13% CP diet fortified with LM plus CA. 16. Statistical analysis did not reveal any significant (P>0.05) alternations among dietary treatments as for serum biochemical parameters. 17. Results elucidated that 13% CP in the diet with adding LM as control diet recorded significantly (P≤0.05) the highest value of digestibility coefficient of organic matter (OM), ether extract (EE), nitrogen free extract (NFE) and crude fiber (CF) as compared to the control diet. 18. No significant (P≥0.05) effect in previous estimates to digestibility coefficient could be detected among the other dietary treatments and control diet with exception NFE where, it significantly (P≤0.05) improved by feeding on 14% CP with adjusting some LM as control diet. 19. Regarding digestibility coefficient of OM, EE and NFE, no significant differences between the diets contained 13% CP with LM and those contained 14% CP with adding LM and 0.2% CA together. 20. Ash retention was significantly (P≤0.05) improved due to the diet contained 14% CP with LM+CA compared to the control diet. 21. Nitrogen intake (NI) was significantly decreased by usage diet contained 14% CP supplemented with LM compared to the control diet. Also, reduction CP in diet up to 13% with LM led to significantly (P≤0.05) lower nitrogen excreted (NE) than the control diet by about 28.78%, while the diet contained 13% CP with LM+0.2% CA recorded the highest value of NE compared to the control and other diets. 22. Moreover, results of nitrogen retention (NR) proved that feeding on 14% CP supplemented with 0.2% CA were significantly (P≤0.05) better than the control diet by about 10.38%. 23. Chick’s final body weight was significantly increased as a subsequent effect due to feeding the hens on diet contained 14 and 13% CP with LM, 14% CP supplemented with 0.2% CA/kg diet and 14% CP with LM+CA together comparing with the control diet. 24. Chicks hatched from eggs of hens fed low CP diets (14 and 13% CP) with LM and 14% CP with LM+CA had significantly higher weight gain than those hatched from eggs of hens fed the control diet. 25. Regarding feed intake/chick/day, the chicks hatched from fertile eggs of hens fed 13% CP with LM and 14% with CA recorded significantly the highest value of FI/chick/day compared to the control diet. 26. On the other hand, chicks from hens fed 14% CP supplemented with LM had the best feed conversion ratio comparing with the control and other treatments. In addition, all dietary treatments led to a significantly improvement in viability % as compared to the control diet. 27. The results clarified that chicks hatched from fertile eggs of hens fed low CP diet which contained 14 or 13% CP supplemented with LM, CA or their mixture had significantly higher value of total protein and albumin in blood serum than those of the control diet. 28. Also, feeding hens on 13% CP with mixture LM and CA resulted in a significant increase in serum globulin as a subsequent effect in hatched chicks comparing with chicks hatched from hens fed the control diet. 29. It could be noted that all dietary treatments did not significantly (P >0.05) differ from the control diet in respect of EEF of Sinai laying hens except for hens fed the diet containing 14% CP supplemented with 0.2% CA which achieved significantly inferior EEF to that of the control group. 30. All dietary treatments led to insignificant improve in EEF of hatchability of set eggs, but hens fed diet contained 13, 14% CP with 0.2% CA and 14% CP with LM+0.2% CA together achieved better values than control group by about 28.98, 21.07 and 13.17% respectively. These results demonstrate that the reduction requirements for crude protein from 15% for Sinai laying hens up to 14% with supplementation LM alone, 14% CP with 0.2% citric alone and 13, 14% CP with LM supplementation as control diet + 0.2% citric acid together can be used without any adverse effect on productive and economic performance. In fact, when 0.2% citric acid was added with lysine and methionine, egg production records were higher than citric acid or amino acids alone suggesting synergistic effect. Thus, these results imply an important role for 0.2% citric acid and citric acid + some essential amino acids (lysine and methionine) to restore or compensate the decrease in crude protein in Sinai layer’s diet.