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An experiment was conducted to determine the dietary digestible lysine requirement of male and female broiler chickens (Arian) during the period from 6 to 21 days post-hatching. An amino acid-fortified basal diet containing corn and soybean meal as intact protein sources provided 20 % CP, and 3200 kcal AMEn / kg. In this experiment 150 male and 150 female chicks were allocated on the basis of BW to 12 treatments in a factorial arrangement (two sexes at six digestible lysine levels) with five replications of five chicks each in a completely randomized design (CRD). The digestible lysine levels fed were 0.85, 0.95, 1.05, 1.15, 1.25 and 1.35%. The growth rate and feed efficiency of birds fed the basal diet fortified with a surfeit level of l-Lysine-HCl were equal to those of birds fed a corn-soybean meal positive control diet. Average body-weight gain (ABWG) and gain: feed (GF) responded quadratically (P<0.05) to incremental dietary lysine addition. Subjecting the growth data to broken-line analysis indicated that the digestible lysine requirement for maximum body weight gain was 1.075% for males and 1.049% for females. The lysine requirement for maximum feed efficiency was 1.179% for males and 1.149% for females. Male chicks required a higher level of dietary lysine than females for both maximal ABWG and GF. Regardless of sex, 8.8% more digestible lysine (percentage of diet) was required for maximal GF than that needed for maximal ABWG.

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An experiment was conducted to reevaluate the digestible lysine requirement of Arian male broilers by comparing the performance of chicks fed different levels of cottonseed meal (CSM) on a total amino acid (AA) versus a digestible AA basis. Four hundred and thirty two (432) Arian male broiler chicks were allotted to 18 treatments with four repli-cates of six chicks each in a completely randomized block design in a factorial arrange-ment with two factors (two levels of digestible lysine  nine different diets). The first of the eighteen treatments was the corn and soybean meal control diet based on previously de-termined digestible lysine requirement for maximum body weight gain. Diets 2 to 5 con-tained 5, 10, 15 or 20% CSM, respectively and were formulated to contain levels of total AA equivalent to those in the first treatment. Diets 6 to 9 contained the same levels of CSM as diets 2 to 5 but the diets were formulated to be equal in digestible AA content to the first treatment. Treatments 10 to 18 were the same as treatments 1 to 9, but on the ba-sis of determined digestible lysine requirement for maximum feed efficiency. Formulating diets containing CSM on a digestible AA basis resulted in an improvement in chick per-formance compared to those formulated on a total AA basis (P<0.01). The lessening of chick performance with diets formulated on a total AA basis compared to a digestible AA basis, indicated that the previously determined digestible lysine requirement for the Arian broiler strain may be correct.

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Two experiments were conducted to determine the effect of phytase supplementation on layer hens and broiler chickens performance and compare the use of phytase nutrient equivalency values in feed formulation with those fed conventional diet. In the first ex-periment, 640 commercial broiler chicks were used from 11 to 49 days of age. The ex-perimental units were allocated at random to 4 dietary treatments two sexes with 4 rep-licates per treatment. The first dietary treatment was formulated with no addition of phy-tase (C), the second diet contained 500 FTU kg-1 phytase over the top (C+P), and the third diet contained 500 FTU kg-1 phytase which was calculated as half of the nutrient equiva-lency values for phyatse (50E). The fourth dietary treatment contained 500 FTU kg-1 phyatse which was calculated as the total nutrient equivalency values for phytase (100E). In the second experiment 288 Hy-line W-36 hens were used from 60 to 72 weeks of age. The treatments consisted of a control diet (C) with no addition of phytase, a control diet supplemented with 300 FTU kg-1 phytase over the top (C+P), and a third diet containing 300 FTU kg-1 phytase which was calculated as the total nutrient equivalency values for phyatse (100E). No significant difference was observed among the four dietary treatments for broiler final body weight, feed conversion ratio (FCR) and carcass characteristics (P> 0.05). The toe ash, and toe ash Ca and P percentage of broiler chickens increased with the addition of phytase (P< 0.05). Hen day egg production for the C, C+P and 100E group were 75.25, 77.25 and 66.0%, respectively; as egg production declined, FCR increased significantly (P< 0.05). There were no significant differences in egg specific gravity, egg shell thickness, shell breaking strength and egg and toe mineralization among the dietary treatments. The results of the present study indicated that using phytase nutrient equiva-lency in feed formulation has a beneficial effect on broiler performance, but did not have any beneficial effect on the performance of old layer hens. In conclusion, using the same AME and protein equivalency values of phytase for broiler and old layers is not a valid approach.

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The objective of this study was to determine the effects of 8 levels of threonine (0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 and 1.1%) and 2 levels of protein (17.5 and 20.5%) on growth performance, gut sizes and morphology as well as to estimate Standardized Ileal Digestible (SID) Thr requirements in Ross 308 males at 0 to 21 days of age. Chicks were randomized into 64 battery cages (5 chicks per replicate). FI was lower for broiler given the high CP diets as compared to those fed on low CP diets. BWG and FCR improved up to 0.7% Thr in both CP levels. Fitted broken lines indicated break points at 0.62 and 0.66% SID Thr for weight gain at 17.5 and 20.5% crude protein, respectively. Significant interaction was found between CP and Thr on relative weight and length of duodenum and jejunum (P< 0.05). Thr supplementation significantly affected villus height, epithelial thickness, goblet cell number and crypt depth in duodenum, jejunum and ileum (P< 0.01). Low CP diets adequate in Lys, Total Sulfur Amino Acid (TSAA) supplemented with Thr may result in optimal BWG and FCR as well as in growth of intestinal length. Such parameters of gut functionality as microvilli height, crypt depth and epithelial thickness seemed to be improved with even higher levels of dietary SID Thr levels.

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Changes in dietary electrolyte balance influence the metabolic fate of protein and many amino acids. Furthermore, acid-base condition is achieved in part by the alteration of dietary amino acids pattern and quantity. Therefore, a trial was conducted in a completely randomized design to evaluate performance, carcass characteristics, plasma electrolyte and uric acid concentrations of 19 and 28-day-old male broilers fed three experimental diets in which CP was decreased in a stepwise manner from 21 to 18%. Ileal digestible quantities of all EAA were almost equal in the diets, and the total amount of each EAA was maintained at or above NRC 1994 requirements. Decreasing dietary CP did not affect performance and appetite but increased fat deposition in the whole body and abdominal cavity, significantly. High crude protein fed chickens generally produced breast, thighs and total carcasses that were lower in fat. Reducing dietary CP increased the concentrations of main plasma electrolytes including ionized forms of the electrolytes (Na+, K+, Cl-) but its influence on Ca++ and HCO3- ions was not significant. On the other hand, plasma uric acid concentration was reduced in parallel with crude protein reduction. Therefore, although reduction of CP to 18% does not impair the performance of broiler chickens, deficiency in uric acid production in low CP diets may lead to blood electrolyte imbalance.

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Some reports indicate a wide range for Zn requirements for broiler chickens i.e. from 10.6 to 105 mg kg^-1. A number of factors other than dietary Zn concentration determine the need for supplementation, principally dietary phytate. Therefore, the objective of the present investigation was reevaluation of the zinc requirement for broiler, fed practical diet supplemented with phytase in a dose-response trial. A total of 768 male Ross 308 broiler chicks were used. Basal corn-soy diet deficient in Zn was supplemented with experimental diets for making 16 dietary treatments. Experimental design was a completely randomized design in a 4×4 factorial arrangement. Factors included four levels of dietary zinc (24, 54, 84 and 114 mg kg^-1) and phytase (0, 100, 200, 300 FTU kg^-1). Treatments were replicated four times and each had 12 birds. Linear and nonlinear functions were derived for graded levels of zinc and phytase. Results indicated that effect of dietary zinc on body weight at 42 days of age was significant (P< 0.01). The fitted quadratic model estimated 66.7, 64.8, and 60.1 mg kg^-1 zinc requirement for body weight at 28, 35, and 42 days of age, respectively (P< 0.001), while the fitted two slope broken line estimated 53.5, 53.8 and 57.4 mg kg^-1 zinc requirement for body weight at the same ages, respectively (P< 0.002). Zinc equivalence value of phytase was estimated to be 0.225 mg kg^-1 FTU^-1 and added phytase increased liver zinc storage too (P< 0.01). Estimated zinc requirement for body weight by using practical high phytate diet, low availability source of Zn, and exogenous phytase was lower than Ross 308 recommendation (60 vs 100 mg kg^-1).

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The effects of Zinc Oxide (ZnO) and E. Coli-derived 6-phytase supplemented-diet on the reproductive performance in aged broiler breeder hens and on immune responses of their progeny chicks were studied. In a 2×4 factorial arrangement, 2 inclusion levels (0 or 300 U kg^-1 diet) of E. coli-derived phytase and 4 inclusion levels (30, 60, 90, and 120 mg kg-¹ diet) of ZnO were provided from 62 throughout 72 weeks of age. A total of 128 hens were randomly assigned into 8 dietary treatments with 4 replicates of 4 hens each. During 66 to 71 weeks of age, egg production and egg weights were daily recorded. Results showed that ZnO and ZnO×phytase interaction affected the egg weight and fertility rate (P< 0.01). Adding ZnO and phytase to diet increased the relative weight of bursa of Fabricius and liver in the hatchlings. Also, the interactive effect of ZnO and phytase on the relative weight of heart was significantly affected by the hatchlings (P< 0.01). In conclusion, dietary supplementation of ZnO and E. coli-derived 6-phytase profoundly improved the fertility rate in aged broilers breeder hens, although the effects on immunity of their progeny were negligible.

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One hundred ninety two broiler breeder hens, from 40 to 49 weeks of age, were utilized in a precision feeding study for determining the hens’ energy requirement. Treatments were daily feed allotments containing metabolizable Energy Requirement (ER) estimated by empirical model, ER minus 10 (ER‒10), plus 10 (ER+10), and plus 20 kcal hen^-1 d^-1 (ER+20). Four levels of Metabolizable Energy Intake (MEI) were made by adding 0, 1.2, 2.4 and 3.6 grams corn oil, over the top of daily feed allotment. All birds consumed the same amount of diet, and were provided the same intake of nutrients, except energy. Hens with weight gain of 3.5 g per day had the maximum reproductive performance. Ovary weights were lower in ER-10 hens. This difference was also reflected in Small Yellow Follicle (SYF), and Large Yellow Follicle (LYF) numbers, in which the ER-10 hens had fewer SYF (7.6) and LYF (1.1). Hens that received 462.7 kcal d^-1 (ER), produced 4.04 eggs more than those that received 452.7 kcal d^-1 (ER‒10). However, addition of extra 10 and 20 kcal (ER+10, ER+20) on daily MEI had no beneficial effect on egg production. Using the linear broken line model, the ME requirements for egg production and hatchability were estimated at 458.5, and 456.2 kcal hen^-1 d^-1, respectively. Comparing the current estimated requirement value with earlier reports revealed that broiler breeder hens need more energy in a commercial house than those kept in an experimental house in the cage or pen. In conclusion, during post peak period with average 458.5 kcal MEI, 5 kcal hen^-1 d^-1 more than Ross 308 recommendation can improve broiler breeder hens’ performance.

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This experiment was conducted to determine whether 6-phytase has a positive effect on zinc requirements, production performance, and zinc content of tissues in broiler breeders at the end of their production cycle. One hundred and twenty-eight obese Cobb-500 broiler breeder hens (>v4.9 kg) were weighed at 58 weeks of age and assigned to various treatment groups. To deplete the zinc reserves in hens, they were given a zinc-deficient diet (9.5 mg kg^-1 of zinc) and drank water with 35 μg L^-1 zinc for two weeks. Then, hens were randomly allocated to 8 dietary treatments in a factorial arrangement of two levels of phytase (0, 300 FTU kg^-1) and four levels of dietary zinc (30, 60, 90, 120 mg kg^-1) with four replicates of 4 hens in each. Bodyweight, egg production, egg weight, and egg quality were measured during the five-week experimental period. Added zinc significantly increased yolk weight and zinc content of yolk (P< 0.05) and plasma (P< 0.0001). Egg weight was significantly increased by adding phytase (P< 0.05). As the results of this experiment show, adding exogenous phytase can decrease the zinc requirement of broiler breeder hens by releasing 16.9% of the zinc bound to phytate.