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Production Performance and Egg Quality of Hy-Line W36 Laying Hens Fed Reduced-Protein Diets at a Constant Total Sulfur Amino Acid:Lysine Ratio
©2008 Poultry Science Association, Inc.
Production Performance and Egg Quality of Hy-Line W36 Laying Hens Fed Reduced-Protein Diets at a Constant Total Sulfur Amino Acid:Lysine Ratio F. Khajali,* E. A. Khoshouie,* S. K. Dehkordi,†1 and M. Hematian*
Primary Audience: Commercial Layer Managers, Nutritionists
SUMMARY Two hundred eight 20-wk-old Hy-Line W36 hens at a 5% production rate were assigned to 2 dietary treatments varying in CP content. Each treatment consisted of 13 replicates of 8 hens. Dietary CP levels of the control diet were 17.8, 19.9, 18.5, and 15.5% during the periods of 1) a 5 to 50% production rate, 2) a 50% production rate until mo 7, 3) mo 8 to 10 of the production cycle, and 4) mo 10 to 12 of the production cycle, respectively. The respective CP levels of the reduced-CP diet fed during these phases were 16.3, 18.4, 17.0, and 13.9%. The reduced-CP diets had dietary CP levels approximately 1.5 percentage units lower than their control counterparts. Dietary treatments met the minimal requirements for amino acids recommended by NRC (1994). Hen-day egg production, egg mass, and FCR were maintained well on the low-protein diet during the first 8 mo of production but tended to be impaired thereafter. In mo 10 and 11 of the laying period, egg mass was significantly (P < 0.05) reduced and FCR was significantly (P < 0.05) impaired on the reduced-CP diet compared with the control diet. Egg weight, eggshell thickness, eggshell breaking strength, and albumen height were not significantly affected by feeding the reduced-CP diet. In conclusion, layer performance can remain satisfactory on reduced-CP diets for short periods, but long-term feeding of reduced-CP diets may not be advisable because it will reduce performance in the late stage of production. Key words: egg quality, laying hen, performance, protein 2008 J. Appl. Poult. Res. 17:390–397 doi:10.3382/japr.2008-00002
DESCRIPTION OF PROBLEM Commercial laying hen diets consist of essential amino acids ranging in concentration from 122 to 275% of the requirement [1]. Amino acids in excess of the requirements impair pro1
Corresponding author: [email protected]
duction performance through numerous interactions and result in environmental pollution with nitrogen [1]. The most feasible strategy for coping with this problem is the partial replacement of the intact dietary protein with crystalline amino acids. The potential for reducing dietary
Downloaded from http://japr.oxfordjournals.org/ at University of Otago Science Library on December 21, 2014
*Department of Animal Science, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran, 88186-34141; and †Laboratory for Animal Nutrition, Department of Animal Production, University of Ghent, 9090 Ghent, Belgium
Khajali et al.: REDUCED-PROTEIN DIET FOR LAYERS
MATERIALS AND METHODS Two hundred eight 20-wk-old Hy-line W36 hens [8] were housed in an environmentally controlled cage system. Each cage (45 × 50 cm) accommodated 4 hens, and 2 adjacent cages (cage pair) were considered a treatment replicate. Thir-
teen cage pairs were randomly assigned to each treatment group. Two dietary treatments varying in protein content were used: 1) a control diet that met NRC [7] recommendations for amino acids and that was fed according to the Hy-Line W36 management guide [8], and 2) a reducedCP diet with approximately 1.5% lower CP than the control diet in all feeding phases so that none of the essential amino acids was limiting, except for Met and Lys . Consequently, the reduced-CP diet was supplemented with Met and Lys so that the ratio of TSAA:Lys was kept similar to the ratio in the control diet in each stage. Although the levels of other amino acids were not similar between the control and reduced-CP diets, they were not limiting. A phase feeding program (phase I: 20 wk of age, when the flock was at 5% egg production, until 50% egg production; phase II: 50% egg production to 50 wk of age; phase III: 51 to 62 wk of age; phase IV: 63 to 72 wk of age) was used during the experiment (20 to 72 wk of age). Table 1 presents the composition of the experimental diets during the feeding phases. All experimental diets and all protein sources were analyzed for CP before the beginning of the experiment [9]. To determine amino acids, duplicate samples of each diet were subjected to 6 N HCl and hydrolyzed for 24 h at 110°C [10]. After acid hydrolysis, all samples were analyzed for amino acid content by using an ion-exchange chromatograph (LKB Biochrom 4141) [11]. Performic acid oxidation was done to determine sulfur amino acids, and Met was measured as methionyl sulfone [12]. Feed and water were provided freely. Body weights of the hens were determined at the beginning and end of the experiment. The photoperiod was 16L:8D throughout the experiment. Daily records of egg production and feed consumption, and monthly records of egg weight were kept and were summarized as hen-day egg production, egg mass, and FCR on a monthly basis. The parameters relative to egg quality were evaluated before peak, at peak, and every 3 mo postpeak. Two eggs were randomly collected per treatment replicate to determine these parameters. The collected eggs were weighed (±0.01 g), and each egg was then exposed to a pressing force by using an eggshell strength meter. On breaking, the egg contents were poured
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protein has become a reality because of the commercial availability of Lys, Met, Thr, and Trp on the market [2]. Several studies have examined the effects of low-protein diets in laying hen nutrition. In an early work, Keshavarz [3] observed lower BW at 20 wk and decreased performance during the early phase of the egg production cycle when pullets were given low-protein diets during the rearing period. Hsu et al. [4] evaluated the layer response to either a low-protein (14%) or control (17%) diet in a 5-wk experimental period and found similar responses to both diets in terms of egg production and FCR. Blair et al. [5] compared a 13.5% CP diet with a control diet (17% CP) on layer performance. They concluded that layer performance could be maintained well on the low-protein diet when diets were properly supplemented with essential amino acids. At the same time, nitrogen excretion was reduced by 30 to 35%. More recently, Junqueira et al. [6] indicated that the performance of laying hens in the second laying cycle of an 8-wk experiment was comparable between the 16 and 20% CP diets. The studies evaluated the response of laying hens to reduced-CP diets in a short period, but they did not maintain a constant TSAA:Lys ratio among the diets. Because Met and Lys are the most limiting amino acids in corn-soybean meal diets for laying hens, the purpose of the present study was to compare a reduced-CP diet with a control diet at the same TSAA:Lys ratio. The control diet satisfied NRC [7] minimal requirements. The reduced-CP diet was prepared in a manner such that none of the essential amino acids was limiting, except for Met and Lys. In fact, the extent of the reduction in dietary CP was as great as Met and Lys were limiting; consequently, their dietary levels were kept similar to that of the control diet by supplementing these 2 amino acids. The effect of feeding the dietary protein regimens in an entire production cycle was studied.
391
60 21.5 — 4.5 3.2 1.1 8.6 0.4 0.2 — 0.25 0.25 2,905 17.8 0.82 0.95 0.86 0.64 0.21 1.09 0.80 0.95 0.62 0.20 1.02
Corn Soybean meal (44% CP) Wheat bran Fish meal (64% CP) Soybean oil Dicalcium phosphate Oyster shell Salt dl-Met l-Lys·HCl Vitamin premix1 Trace mineral premix2 ME (kcal/kg) CP (%) Met + Cys3 (%) Lys3 (%) TSAA:Lys Thr3 (%) Trp3 (%) Arg3 (%) Met + Cys4 (%) Lys4 (%) Thr4 (%) Trp4 (%) Arg4 (%)
64.2 17.2 0.4 4.5 2.7 1.1 8.7 0.3 0.25 0.1 0.25 0.25 2,911 16.3 0.82 0.95 0.86 0.58 0.19 0.97 0.81 0.95 0.56 0.18 0.95
Low-CP 46 31.2 — 3 6.5 2 10.2 0.4 0.18 — 0.25 0.25 2,916 19.9 0.86 1.10 0.78 0.74 0.24 1.28 0.85 1.10 0.74 0.22 1.21
Control 52 26.4 — 3 5.3 2 10.2 0.4 0.24 0.05 0.25 0.25 2,900 18.4 0.86 1.10 0.78 0.69 0.22 1.15 0.85 1.10 0.65 0.20 1.09
Low-CP
Phase II (50% production to mo 7)
55 24.5 — 4 3.5 1.5 10.5 0.4 0.15 — 0.25 0.25 2,822 18.5 0.80 1.05 0.76 0.67 0.22 1.14 0.78 1.01 0.64 0.21 1.10
Control 60.7 20 — 4 2.4 1.5 10.4 0.4 0.18 — 0.25 0.25 2,815 17.0 0.80 1.05 0.76 0.61 0.19 1.03 0.78 1.02 0.59 0.19 1.00
Low-CP
Phase III (mo 8 to 10 in production)
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Low-CP 69 12 3 3 1.5 1.0 9.5 0.35 0.12 0.1 0.25 0.25 2,840 13.9 0.60 0.79 0.76 0.54 0.14 0.80 0.59 0.76 0.52 0.14 0.79
Control 65 15.5 2.0 4.0 2.0 1.0 9.5 4.0 0.1 — 0.25 0.25 2,840 15.5 0.60 0.79 0.76 0.55 0.17 0.91 0.58 0.77 0.53 0.16 0.90
Phase IV (mo 10 to 12 in production)
Provide (per kg of diet): 12,500 IU of vitamin A; 1,250 IU of vitamin D3; 1.25 IU of vitamin E; 4.4 mg of vitamin K3; 1.5 mg of vitamin B1; 5 mg of vitamin B2; 2.5 mg of vitamin B6; 0.1 mg of vitamin B12; 0.8 g of choline chloride. 2 Provide (per kg of diet): 0.12 g of MnO, 0.375 g of FeSO4, 84 mg of ZnO, 24 mg of CuSO4, and 1.4 mg of CaI2. 3 Calculated values. 4 Analyzed values.
1
Control
Item
Phase I (5 to 50% production)
Table 1. Composition of the experimental diets throughout the laying period (20 to 72 wk)
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Khajali et al.: REDUCED-PROTEIN DIET FOR LAYERS
RESULTS AND DISCUSSION The calculated CP content and amino acid composition of the treatments showed very close agreement with their analyzed values (Table 1). Hen-day egg production was lower in the lowprotein group compared with the control group in the last 4 mo of the experimental period (Figure 1). Data analysis showed a significant difference with respect to treatment and period effects, but their interaction was not significant. The reducing trend of egg production in the reduced-CP group may be explained by taking into account the changes in hen BW. Mean BW at the onset of experiment was 1,242 ± 10.3 g and 1,235.6 ± 7.0
g for the control and reduced-CP groups, respectively; the difference was not significant. At the end of the experiment, however, birds that received the reduced-CP diet had significantly (P < 0.05) lower BW than those that received the control diet (1,514.8 ± 5.3 g vs. 1,482 ± 7.0 g). It seems that body protein reserves were gradually depleted in birds on the reduced-CP diet. In fairness to this observation, Koelkebeck et al. [14] compared 16% CP (control) and 10% CP diets fed after induction of molt. They demonstrated that hens on a 16% CP diet gained weight more rapidly than those fed a 10% CP diet. With respect to egg production, the results of this experiment were in agreement with those reported by Novak et al. [15], who suggested that the effects of the reduced-CP diet were more dramatic during the late stage production (43 to 63 wk of age). Despite the satisfactory results of feeding a reduced-CP diet for short periods [5, 16], feeding reduced-CP diets for a long period can result in poor egg production. Egg weight was not influenced by feeding the reduced-CP diet (Table 2). In contrast, Leeson and Caston [17] reported that egg weight was lower with diets containing 14.4% protein compared with 16.8% protein, although both diets
Figure 1. Hen-day egg production of treatment groups during the experiment. Each treatment consisted of 13 replicates. The statistical difference between treatments was significant (P < 0.05) in March and April.
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into a flat plate to measure the albumen height. Eggshell thickness was determined with a micrometer. No attempt was made to separate the shell membrane before measuring the eggshell thickness. The experimental design consisted of a completely randomized design with repeated measures. A t-test was used to separate the treatment means at each month. The GLM procedure in SAS [13] software was used to analyze the data.
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394 Table 2. Effects of dietary treatments on egg weight (g) throughout the experiment1 Month
Reduced-CP
P-value
43.1 ± 0.055 45.7 ± 1.07 54.1 ± 0.35 57.3 ± 0.22 59.0 ± 0.31 60.7 ± 0.24 61.6 ± 0.35 63.2 ± 0.37 60.9 ± 0.96 62.5 ± 0.37 61.7 ± 0.59 61.8 ± 0.44
43.3 ± 0.61 46.2 ± 0.74 54.3 ± 0.20 57.3 ± 0.20 59.2 ± 0.25 60.3 ± 0.43 62.1 ± 0.44 63.0 ± 0.33 61.6 ± 0.29 61.8 ± 0.35 61.2 ± 0.51 61.8 ± 0.47
0.861 0.671 0.700 0.823 0.560 0.401 0.467 0.668 0.486 0.196 0.485 1.00
1
Each treatment consisted of 13 replicates.
had equal levels of Met and Lys. They attributed the lower egg weight to an inadequate level of total N. In their study, the reduced-CP diet had 2.4 percentage units lower CP than the control diet. In the present study, however, the difference between treatments in terms of CP content was 1.5 percentage units. Comparable egg weights between the reduced-CP and the control groups in the present study suggest that the reducedCP diet was fortified well with essential amino acids and had an adequate level of total N. In a study conducted by Roberts et al. [18], with a similar percentage unit reduction in CP level, egg weight was not affected by the reduced-CP diet, but hens fed the reduced-CP diet produced fewer eggs and, as a result, had lower egg mass compared with the control diet. This discrepancy with the present findings may be due to a difference in essential amino acid balance between treatments, because Roberts et al. [18] did not maintain similar TSAA:Lys between their treatments. Sohail et al. [19] demonstrated that essential amino acids had a significant influence on egg weight so that removing an indispensable amino acid resulted in reduced egg weight within 2 wk. Data analysis showed a significant (P < 0.05) effect of period on egg weight. This would be expected because the egg size is small in the beginning of the laying period and tends to increase with age. We concluded, based on the results of the present study and a review of the relevant literature, that the response in egg production was more sensitive to the reducedCP diets than was egg size.
Egg mass was significantly affected by feeding the reduced-CP diet (Table 3). There was a remarkable reduction in egg mass as a result of feeding the reduced-CP diet in the last months of the experimental period. Egg mass was determined by 2 components: egg weight and egg production. Because egg weight was not affected by dietary treatment, variability in egg mass was due to differences in egg production. The effect of period on egg mass was greatly significant (P < 0.0001), and this was anticipated because a flock beginning egg production lays smaller eggs with a lower egg production rate. The findings pertaining to egg mass are consistent with the report of Novak et al. [15]. Feed intake in the treatments showed a very similar trend so that there was no significant difference between the control and reduced-CP groups (P < 0.05). Average daily feed consumption by each bird was 89 and 88.6 g during the first 2 phases of the production cycle for the control and the reduced-CP groups, respectively. During the last 2 phases of the production cycle, each bird in the control and the reduced-CP groups consumed 102 and 101.5 g/d, respectively. Hence, variation in FCR was due mainly to differences in egg mass. Feed conversion ratio was comparable between the control and reduced-CP groups up to 7 mo in production (Table 4). From then on, however, FCR of the low-protein group was poorer than that of the control so that the difference between treatments was significant (P < 0.05) in mo 10 and 11. The significant differences between the con-
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1 (June 2005) 2 (July 2005) 3 (August 2005) 4 (September 2005) 5 (October 2005) 6 (November 2005) 7 (December 2005) 8 (January 2006) 9 (February 2006) 10 (March 2006) 11 (April 2006) 12 (May 2006)
Control
Khajali et al.: REDUCED-PROTEIN DIET FOR LAYERS
395
Table 3. Effects of dietary treatments on egg mass (g/bird per day) throughout the experiment1 Month
Reduced-CP
P-value
7.8 ± 0.29 43.6 ± 0.42 49.6 ± 0.69 51.2 ± 0.52 50.8 ± 0.64 51.7 ± 0.88 50.6 ± 0.77 51.0 ± 0.79 47.6 ± 0.97 47.4 ± 0.85 44.5 ± 1.02 41.0 ± 1.08
7.5 ± 0.44 44.1 ± 0.78 51.1 ± 0.88 51.2 ± 0.95 50.6 ± 0.86 50.7 ± 0.74 50.2 ± 0.85 50.4 ± 0.93 45.9 ± 0.75 44.7 ± 0.67 41.5 ± 0.93 38.1 ± 1.2
0.507 0.528 0.179 0.961 0.726 0.413 0.768 0.614 0.205 0.032* 0.041* 0.087
1
Each treatment consisted of 13 replicates. *Significant (P < 0.05).
trol and low-protein groups with respect to FCR can be related to the lower egg mass in the lowprotein group (Table 3) because feed intake was similar between treatments (not shown because of similarity). Conversely, Wu et al. [20] indicated that hens fed a 16% CP diet consumed less feed compared with those fed diets containing 15.5 or 14.9% CP. Surprisingly, egg mass was similar between these groups. The discrepancy between their findings and the results reported herein can be explained by the long-term effects of reduced-CP diets. The duration of the study of Wu et al. [20] was 12 wk, whereas that of the present experiment was 52 wk. It should be noted that egg mass was maintained well during the first 12 wk in this study. Table 5 shows the results of egg quality traits before peak, during peak, and every 3 mo post-
peak. In general, there were no significant differences between the control and low-protein groups with respect to albumen height, shell thickness, and shell strength against breaking. However, differences in eggshell strength appeared to be significant at peak production and, opposite the expectation, eggs from the reducedCP group had greater strength against breaking than those of the control group (P = 0.014). This observation is difficult to explain. In our previous study, egg quality indices of pullets fed a reduced-CP diet during the growth stages and up to peak production were not different from those of the control group [21]. This is in agreement with the results of Novak et al. [15], who showed that feeding a low-protein diet to laying hens did not influence shell and internal egg quality measures. The period effect was not sig-
Table 4. Effects of dietary treatments on FCR throughout the experiment1 Month 1 (June 2005) 2 (July 2005) 3 (August 2005) 4 (September 2005) 5 (October 2005) 6 (November 2005) 7 (December 2005) 8 (January 2006) 9 (February 2006) 10 (March 2006) 11 (April 2006) 12 (May 2006) 1
Each treatment consisted of 13 replicates. *Significant (P < 0.05).
Control
Reduced-CP
P-value
3.59 ± 0.16 1.88 ± 0.02 1.79 ± 0.02 1.78 ± 0.02 1.90 ± 0.03 1.90 ± 0.03 1.99 ± 0.03 1.96 ± 0.03 2.11 ± 0.04 2.25 ± 0.05 2.33 ± 0.06 2.38 ± 0.06
3.89 ± 0.29 1.86 ± 0.03 1.74 ± 0.03 1.79 ± 0.04 1.90 ± 0.03 1.93 ± 0.03 1.99 ± 0.03 1.99 ± 0.03 2.19 ± 0.04 2.39 ± 0.03 2.50 ± 0.06 2.57 ± 0.08
0.379 0.639 0.242 0.913 0.674 0.471 0.762 0.589 0.248 0.036* 0.050* 0.081
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1 (June 2005) 2 (July 2005) 3 (August 2005) 4 (September 2005) 5 (October 2005) 6 (November 2005) 7 (December 2005) 8 (January 2006) 9 (February 2006) 10 (March 2006) 11 (April 2006) 12 (May 2006)
Control
JAPR: Research Report
Missed 0.014* 0.750 0.591 0.550
Low-protein
Missed 3.58 ± 0.12 3.29 ± 0.18 3.46 ± 0.16 3.26 ± 0.12
Control
Missed 3.01 ± 0.18 3.19 ± 0.42 3.35 ± 0.52 3.36 ± 0.11
CONCLUSIONS AND APPLICATIONS
0.226 0.928 0.746 0.071 0.881 0.38 ± 0.01 0.38 ± 0.01 0.40 ± 0.01 0.38 ± 0.01 0.39 ± 0.01 0.326 0.828 0.912 0.106 0.830 1
Each treatment consisted of 13 replicates. *Significant (P < 0.05).
4.76 ± 0.34 5.85 ± 0.27 4.48 ± 0.31 4.45 ± 0.35 5.36 ± 0.54 5.26 ± 0.36 5.92 ± 0.16 4.43 ± 0.31 4.35 ± 0.42 5.53 ± 0.57 Prepeak Peak 3 mo postpeak 6 mo postpeak 9 mo postpeak
1. Layer performance is satisfactory on reduced-protein diets for short periods. 2. Long-term feeding of reduced-protein diets will drop the performance in the late stage of production, even though no amino acids are limiting and the TSAA:Lys ratio is the same. This may be due to the gradual depletion of body protein reserves in birds on the reducedCP diet. 3. We recommend that the rotational use of reduced-protein diets during a production cycle be studied.
REFERENCES AND NOTES
0.39 ± 0.01 0.39 ± 0.01 0.40 ± 0.01 0.40 ± 0.02 0.39 ± 0.01
P-value
Low-protein Period
Control
Low-protein
P-value
Control
Shell thickness (mm) Albumen height (mm)
Table 5. Effects of dietary treatments on albumen height, shell thickness, and shell strength during different stages of the experiment1
nificant for shell thickness and strength but was significant for albumen height. Albumen height of eggs at 3 and 6 mo postpeak was surprisingly reduced.
1. Austic, R. E. 1981. On the nature of amino acid interactions. Pages 5–13 in Proc. Cornell Nutr. Conf. for Feed Manufact. Cornell University, Ithaca, NY. 2. Ishibashi, T., and C. Yonemochi. 2003. Amino acid nutrition in egg production industry . Anim. Sci. J. 74:457– 469. 3. Keshavarz, K. 1984. The effect of different dietary protein levels in the rearing and laying period on performance of White Leghorn chickens. Poult. Sci. 63:2229– 2240. 4. Hsu, J. C., C. Y. Lin, and P. W. Chiou. 1998. Effects of ambient temperature and methionine supplementation of a low-protein diet on the performance of laying hens. Anim. Feed Sci. Technol. 74:289–299. 5. Blair, R., J. P. Jacob, S. Ibrahim, and P. A. Wang. 1999. Quantitative assessment of reduced-protein diets and supplements to improve nitrogen utilization. J. Appl. Poult. Res. 8:25–47. 6. Junqueira, O. M., A. C. de Laurentiz, R. da Silva Filardi, E. A. Rodrigues, and E. M. Casartelli. 2006. Effects of energy and protein levels on egg quality and performance of laying hens at early second production cycle. J. Appl. Poult. Res. 15:110–115. 7. National Research Council. 1994. Nutrient Requirements for Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC. 8. Hy-Line International. Hy-Line W36 Commercial Management Guide, Hy-Line Int. USA. 2005. 9. Association of Official Analytical Chemists. 1990. Methods of Analysis. 15th ed. AOAC, Arlington, VA. 10. Andrew, R. P., and N. A. Baldar. 1985. Amino acid analysis of feed constituents. Science Tools. 32:44–48. 11. Pharmacia Biotech (Biochrom) Ltd., Cambridge, UK.
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Shell strength (kg/cm2)
P-value
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18. Roberts, S. A., H. Xin, B. J. Kerr, J. R. Russell, and K. Bregendahl. 2007. Effects of dietary fiber and reduced crude protein on nitrogen balance and egg production in laying hens. Poult. Sci. 86:1716–1725. 19. Sohail, S. S., M. M. Bryant, and D. A. Roland. 2002. Influence of supplemental lysine, isoleucine, threonine, tryptophan and total sulfur amino acids on egg weight of Hy-Line W-36 hens . Poult. Sci. 81:1038–1044. 20. Wu, G., P. Gunawardana, M. M. Bryant, R. A. Voitle, and D. A. Roland. 2007. Effects of dietary energy and protein on performance, egg composition, egg solids, egg quality and profits of Hy-line W-36 hens during phase 3. Jpn. Poult. Sci. 44:52–57. 21. Khajali, F., M. Faraji, and S. Karimi Dehkordi. 2007. Effects of reduced-protein diets at constant total sulfur amino acids:lysine ratio on pullet development and subsequent laying hen performance. Am. J. Anim. Vet. Sci. 2:89–92.
Downloaded from http://japr.oxfordjournals.org/ at University of Otago Science Library on December 21, 2014
12. Moore, S., and W. H. Stain. 1963. Chromatographic determination of amino acids by the use of automatic recording equipment. Methods Enzymol. 6:819–831. 13. SAS Institute. 1997. SAS User’s Guide. SAS Inst. Inc., Cary, NC. 14. Koelkebeck, K. W., C. W. Parsons, R. W. Leeper, and X. Wang. 1993. Effect of supplementation of a low-protein corn molt diet with amino acids on early postmolt laying hen performance. Poult. Sci. 72:1528–1536. 15. Novak, C., H. M. Yakout, and E. Schedeler. 2006. The effect of dietary protein level and total amino acid:lysine ratio on egg production parameters and egg yield in Hy-Line W-98 hens. Poult. Sci. 85:2195–2206. 16. Keshavarz, K., and R. E. Austic. 2004. The use of low-protein, low-phosphorous, amino acid-, and phytasesupplemented diets on laying hen performance and nitrogen and phosphorous excretion . Poult. Sci. 83:75–83. 17. Leeson, S., and L. J. Caston. 1996. Response of laying hens to diets varying in crude protein or available phosphorous. J. Appl. Poult. Res. 5:289–296.
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Production Performance and Egg Quality of Hy-Line W36 Laying Hens Fed Reduced-Protein Diets at a Constant Total Sulfur Amino Acid:Lysine Ratio F. Khajali,* E. A. Khoshouie,* S. K. Dehkordi,†1 and M. Hematian*
Primary Audience: Commercial Layer Managers, Nutritionists
SUMMARY Two hundred eight 20-wk-old Hy-Line W36 hens at a 5% production rate were assigned to 2 dietary treatments varying in CP content. Each treatment consisted of 13 replicates of 8 hens. Dietary CP levels of the control diet were 17.8, 19.9, 18.5, and 15.5% during the periods of 1) a 5 to 50% production rate, 2) a 50% production rate until mo 7, 3) mo 8 to 10 of the production cycle, and 4) mo 10 to 12 of the production cycle, respectively. The respective CP levels of the reduced-CP diet fed during these phases were 16.3, 18.4, 17.0, and 13.9%. The reduced-CP diets had dietary CP levels approximately 1.5 percentage units lower than their control counterparts. Dietary treatments met the minimal requirements for amino acids recommended by NRC (1994). Hen-day egg production, egg mass, and FCR were maintained well on the low-protein diet during the first 8 mo of production but tended to be impaired thereafter. In mo 10 and 11 of the laying period, egg mass was significantly (P < 0.05) reduced and FCR was significantly (P < 0.05) impaired on the reduced-CP diet compared with the control diet. Egg weight, eggshell thickness, eggshell breaking strength, and albumen height were not significantly affected by feeding the reduced-CP diet. In conclusion, layer performance can remain satisfactory on reduced-CP diets for short periods, but long-term feeding of reduced-CP diets may not be advisable because it will reduce performance in the late stage of production. Key words: egg quality, laying hen, performance, protein 2008 J. Appl. Poult. Res. 17:390–397 doi:10.3382/japr.2008-00002
DESCRIPTION OF PROBLEM Commercial laying hen diets consist of essential amino acids ranging in concentration from 122 to 275% of the requirement [1]. Amino acids in excess of the requirements impair pro1
Corresponding author: [email protected]
duction performance through numerous interactions and result in environmental pollution with nitrogen [1]. The most feasible strategy for coping with this problem is the partial replacement of the intact dietary protein with crystalline amino acids. The potential for reducing dietary
Downloaded from http://japr.oxfordjournals.org/ at University of Otago Science Library on December 21, 2014
*Department of Animal Science, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran, 88186-34141; and †Laboratory for Animal Nutrition, Department of Animal Production, University of Ghent, 9090 Ghent, Belgium
Khajali et al.: REDUCED-PROTEIN DIET FOR LAYERS
MATERIALS AND METHODS Two hundred eight 20-wk-old Hy-line W36 hens [8] were housed in an environmentally controlled cage system. Each cage (45 × 50 cm) accommodated 4 hens, and 2 adjacent cages (cage pair) were considered a treatment replicate. Thir-
teen cage pairs were randomly assigned to each treatment group. Two dietary treatments varying in protein content were used: 1) a control diet that met NRC [7] recommendations for amino acids and that was fed according to the Hy-Line W36 management guide [8], and 2) a reducedCP diet with approximately 1.5% lower CP than the control diet in all feeding phases so that none of the essential amino acids was limiting, except for Met and Lys . Consequently, the reduced-CP diet was supplemented with Met and Lys so that the ratio of TSAA:Lys was kept similar to the ratio in the control diet in each stage. Although the levels of other amino acids were not similar between the control and reduced-CP diets, they were not limiting. A phase feeding program (phase I: 20 wk of age, when the flock was at 5% egg production, until 50% egg production; phase II: 50% egg production to 50 wk of age; phase III: 51 to 62 wk of age; phase IV: 63 to 72 wk of age) was used during the experiment (20 to 72 wk of age). Table 1 presents the composition of the experimental diets during the feeding phases. All experimental diets and all protein sources were analyzed for CP before the beginning of the experiment [9]. To determine amino acids, duplicate samples of each diet were subjected to 6 N HCl and hydrolyzed for 24 h at 110°C [10]. After acid hydrolysis, all samples were analyzed for amino acid content by using an ion-exchange chromatograph (LKB Biochrom 4141) [11]. Performic acid oxidation was done to determine sulfur amino acids, and Met was measured as methionyl sulfone [12]. Feed and water were provided freely. Body weights of the hens were determined at the beginning and end of the experiment. The photoperiod was 16L:8D throughout the experiment. Daily records of egg production and feed consumption, and monthly records of egg weight were kept and were summarized as hen-day egg production, egg mass, and FCR on a monthly basis. The parameters relative to egg quality were evaluated before peak, at peak, and every 3 mo postpeak. Two eggs were randomly collected per treatment replicate to determine these parameters. The collected eggs were weighed (±0.01 g), and each egg was then exposed to a pressing force by using an eggshell strength meter. On breaking, the egg contents were poured
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protein has become a reality because of the commercial availability of Lys, Met, Thr, and Trp on the market [2]. Several studies have examined the effects of low-protein diets in laying hen nutrition. In an early work, Keshavarz [3] observed lower BW at 20 wk and decreased performance during the early phase of the egg production cycle when pullets were given low-protein diets during the rearing period. Hsu et al. [4] evaluated the layer response to either a low-protein (14%) or control (17%) diet in a 5-wk experimental period and found similar responses to both diets in terms of egg production and FCR. Blair et al. [5] compared a 13.5% CP diet with a control diet (17% CP) on layer performance. They concluded that layer performance could be maintained well on the low-protein diet when diets were properly supplemented with essential amino acids. At the same time, nitrogen excretion was reduced by 30 to 35%. More recently, Junqueira et al. [6] indicated that the performance of laying hens in the second laying cycle of an 8-wk experiment was comparable between the 16 and 20% CP diets. The studies evaluated the response of laying hens to reduced-CP diets in a short period, but they did not maintain a constant TSAA:Lys ratio among the diets. Because Met and Lys are the most limiting amino acids in corn-soybean meal diets for laying hens, the purpose of the present study was to compare a reduced-CP diet with a control diet at the same TSAA:Lys ratio. The control diet satisfied NRC [7] minimal requirements. The reduced-CP diet was prepared in a manner such that none of the essential amino acids was limiting, except for Met and Lys. In fact, the extent of the reduction in dietary CP was as great as Met and Lys were limiting; consequently, their dietary levels were kept similar to that of the control diet by supplementing these 2 amino acids. The effect of feeding the dietary protein regimens in an entire production cycle was studied.
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60 21.5 — 4.5 3.2 1.1 8.6 0.4 0.2 — 0.25 0.25 2,905 17.8 0.82 0.95 0.86 0.64 0.21 1.09 0.80 0.95 0.62 0.20 1.02
Corn Soybean meal (44% CP) Wheat bran Fish meal (64% CP) Soybean oil Dicalcium phosphate Oyster shell Salt dl-Met l-Lys·HCl Vitamin premix1 Trace mineral premix2 ME (kcal/kg) CP (%) Met + Cys3 (%) Lys3 (%) TSAA:Lys Thr3 (%) Trp3 (%) Arg3 (%) Met + Cys4 (%) Lys4 (%) Thr4 (%) Trp4 (%) Arg4 (%)
64.2 17.2 0.4 4.5 2.7 1.1 8.7 0.3 0.25 0.1 0.25 0.25 2,911 16.3 0.82 0.95 0.86 0.58 0.19 0.97 0.81 0.95 0.56 0.18 0.95
Low-CP 46 31.2 — 3 6.5 2 10.2 0.4 0.18 — 0.25 0.25 2,916 19.9 0.86 1.10 0.78 0.74 0.24 1.28 0.85 1.10 0.74 0.22 1.21
Control 52 26.4 — 3 5.3 2 10.2 0.4 0.24 0.05 0.25 0.25 2,900 18.4 0.86 1.10 0.78 0.69 0.22 1.15 0.85 1.10 0.65 0.20 1.09
Low-CP
Phase II (50% production to mo 7)
55 24.5 — 4 3.5 1.5 10.5 0.4 0.15 — 0.25 0.25 2,822 18.5 0.80 1.05 0.76 0.67 0.22 1.14 0.78 1.01 0.64 0.21 1.10
Control 60.7 20 — 4 2.4 1.5 10.4 0.4 0.18 — 0.25 0.25 2,815 17.0 0.80 1.05 0.76 0.61 0.19 1.03 0.78 1.02 0.59 0.19 1.00
Low-CP
Phase III (mo 8 to 10 in production)
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Low-CP 69 12 3 3 1.5 1.0 9.5 0.35 0.12 0.1 0.25 0.25 2,840 13.9 0.60 0.79 0.76 0.54 0.14 0.80 0.59 0.76 0.52 0.14 0.79
Control 65 15.5 2.0 4.0 2.0 1.0 9.5 4.0 0.1 — 0.25 0.25 2,840 15.5 0.60 0.79 0.76 0.55 0.17 0.91 0.58 0.77 0.53 0.16 0.90
Phase IV (mo 10 to 12 in production)
Provide (per kg of diet): 12,500 IU of vitamin A; 1,250 IU of vitamin D3; 1.25 IU of vitamin E; 4.4 mg of vitamin K3; 1.5 mg of vitamin B1; 5 mg of vitamin B2; 2.5 mg of vitamin B6; 0.1 mg of vitamin B12; 0.8 g of choline chloride. 2 Provide (per kg of diet): 0.12 g of MnO, 0.375 g of FeSO4, 84 mg of ZnO, 24 mg of CuSO4, and 1.4 mg of CaI2. 3 Calculated values. 4 Analyzed values.
1
Control
Item
Phase I (5 to 50% production)
Table 1. Composition of the experimental diets throughout the laying period (20 to 72 wk)
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Khajali et al.: REDUCED-PROTEIN DIET FOR LAYERS
RESULTS AND DISCUSSION The calculated CP content and amino acid composition of the treatments showed very close agreement with their analyzed values (Table 1). Hen-day egg production was lower in the lowprotein group compared with the control group in the last 4 mo of the experimental period (Figure 1). Data analysis showed a significant difference with respect to treatment and period effects, but their interaction was not significant. The reducing trend of egg production in the reduced-CP group may be explained by taking into account the changes in hen BW. Mean BW at the onset of experiment was 1,242 ± 10.3 g and 1,235.6 ± 7.0
g for the control and reduced-CP groups, respectively; the difference was not significant. At the end of the experiment, however, birds that received the reduced-CP diet had significantly (P < 0.05) lower BW than those that received the control diet (1,514.8 ± 5.3 g vs. 1,482 ± 7.0 g). It seems that body protein reserves were gradually depleted in birds on the reduced-CP diet. In fairness to this observation, Koelkebeck et al. [14] compared 16% CP (control) and 10% CP diets fed after induction of molt. They demonstrated that hens on a 16% CP diet gained weight more rapidly than those fed a 10% CP diet. With respect to egg production, the results of this experiment were in agreement with those reported by Novak et al. [15], who suggested that the effects of the reduced-CP diet were more dramatic during the late stage production (43 to 63 wk of age). Despite the satisfactory results of feeding a reduced-CP diet for short periods [5, 16], feeding reduced-CP diets for a long period can result in poor egg production. Egg weight was not influenced by feeding the reduced-CP diet (Table 2). In contrast, Leeson and Caston [17] reported that egg weight was lower with diets containing 14.4% protein compared with 16.8% protein, although both diets
Figure 1. Hen-day egg production of treatment groups during the experiment. Each treatment consisted of 13 replicates. The statistical difference between treatments was significant (P < 0.05) in March and April.
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into a flat plate to measure the albumen height. Eggshell thickness was determined with a micrometer. No attempt was made to separate the shell membrane before measuring the eggshell thickness. The experimental design consisted of a completely randomized design with repeated measures. A t-test was used to separate the treatment means at each month. The GLM procedure in SAS [13] software was used to analyze the data.
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394 Table 2. Effects of dietary treatments on egg weight (g) throughout the experiment1 Month
Reduced-CP
P-value
43.1 ± 0.055 45.7 ± 1.07 54.1 ± 0.35 57.3 ± 0.22 59.0 ± 0.31 60.7 ± 0.24 61.6 ± 0.35 63.2 ± 0.37 60.9 ± 0.96 62.5 ± 0.37 61.7 ± 0.59 61.8 ± 0.44
43.3 ± 0.61 46.2 ± 0.74 54.3 ± 0.20 57.3 ± 0.20 59.2 ± 0.25 60.3 ± 0.43 62.1 ± 0.44 63.0 ± 0.33 61.6 ± 0.29 61.8 ± 0.35 61.2 ± 0.51 61.8 ± 0.47
0.861 0.671 0.700 0.823 0.560 0.401 0.467 0.668 0.486 0.196 0.485 1.00
1
Each treatment consisted of 13 replicates.
had equal levels of Met and Lys. They attributed the lower egg weight to an inadequate level of total N. In their study, the reduced-CP diet had 2.4 percentage units lower CP than the control diet. In the present study, however, the difference between treatments in terms of CP content was 1.5 percentage units. Comparable egg weights between the reduced-CP and the control groups in the present study suggest that the reducedCP diet was fortified well with essential amino acids and had an adequate level of total N. In a study conducted by Roberts et al. [18], with a similar percentage unit reduction in CP level, egg weight was not affected by the reduced-CP diet, but hens fed the reduced-CP diet produced fewer eggs and, as a result, had lower egg mass compared with the control diet. This discrepancy with the present findings may be due to a difference in essential amino acid balance between treatments, because Roberts et al. [18] did not maintain similar TSAA:Lys between their treatments. Sohail et al. [19] demonstrated that essential amino acids had a significant influence on egg weight so that removing an indispensable amino acid resulted in reduced egg weight within 2 wk. Data analysis showed a significant (P < 0.05) effect of period on egg weight. This would be expected because the egg size is small in the beginning of the laying period and tends to increase with age. We concluded, based on the results of the present study and a review of the relevant literature, that the response in egg production was more sensitive to the reducedCP diets than was egg size.
Egg mass was significantly affected by feeding the reduced-CP diet (Table 3). There was a remarkable reduction in egg mass as a result of feeding the reduced-CP diet in the last months of the experimental period. Egg mass was determined by 2 components: egg weight and egg production. Because egg weight was not affected by dietary treatment, variability in egg mass was due to differences in egg production. The effect of period on egg mass was greatly significant (P < 0.0001), and this was anticipated because a flock beginning egg production lays smaller eggs with a lower egg production rate. The findings pertaining to egg mass are consistent with the report of Novak et al. [15]. Feed intake in the treatments showed a very similar trend so that there was no significant difference between the control and reduced-CP groups (P < 0.05). Average daily feed consumption by each bird was 89 and 88.6 g during the first 2 phases of the production cycle for the control and the reduced-CP groups, respectively. During the last 2 phases of the production cycle, each bird in the control and the reduced-CP groups consumed 102 and 101.5 g/d, respectively. Hence, variation in FCR was due mainly to differences in egg mass. Feed conversion ratio was comparable between the control and reduced-CP groups up to 7 mo in production (Table 4). From then on, however, FCR of the low-protein group was poorer than that of the control so that the difference between treatments was significant (P < 0.05) in mo 10 and 11. The significant differences between the con-
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1 (June 2005) 2 (July 2005) 3 (August 2005) 4 (September 2005) 5 (October 2005) 6 (November 2005) 7 (December 2005) 8 (January 2006) 9 (February 2006) 10 (March 2006) 11 (April 2006) 12 (May 2006)
Control
Khajali et al.: REDUCED-PROTEIN DIET FOR LAYERS
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Table 3. Effects of dietary treatments on egg mass (g/bird per day) throughout the experiment1 Month
Reduced-CP
P-value
7.8 ± 0.29 43.6 ± 0.42 49.6 ± 0.69 51.2 ± 0.52 50.8 ± 0.64 51.7 ± 0.88 50.6 ± 0.77 51.0 ± 0.79 47.6 ± 0.97 47.4 ± 0.85 44.5 ± 1.02 41.0 ± 1.08
7.5 ± 0.44 44.1 ± 0.78 51.1 ± 0.88 51.2 ± 0.95 50.6 ± 0.86 50.7 ± 0.74 50.2 ± 0.85 50.4 ± 0.93 45.9 ± 0.75 44.7 ± 0.67 41.5 ± 0.93 38.1 ± 1.2
0.507 0.528 0.179 0.961 0.726 0.413 0.768 0.614 0.205 0.032* 0.041* 0.087
1
Each treatment consisted of 13 replicates. *Significant (P < 0.05).
trol and low-protein groups with respect to FCR can be related to the lower egg mass in the lowprotein group (Table 3) because feed intake was similar between treatments (not shown because of similarity). Conversely, Wu et al. [20] indicated that hens fed a 16% CP diet consumed less feed compared with those fed diets containing 15.5 or 14.9% CP. Surprisingly, egg mass was similar between these groups. The discrepancy between their findings and the results reported herein can be explained by the long-term effects of reduced-CP diets. The duration of the study of Wu et al. [20] was 12 wk, whereas that of the present experiment was 52 wk. It should be noted that egg mass was maintained well during the first 12 wk in this study. Table 5 shows the results of egg quality traits before peak, during peak, and every 3 mo post-
peak. In general, there were no significant differences between the control and low-protein groups with respect to albumen height, shell thickness, and shell strength against breaking. However, differences in eggshell strength appeared to be significant at peak production and, opposite the expectation, eggs from the reducedCP group had greater strength against breaking than those of the control group (P = 0.014). This observation is difficult to explain. In our previous study, egg quality indices of pullets fed a reduced-CP diet during the growth stages and up to peak production were not different from those of the control group [21]. This is in agreement with the results of Novak et al. [15], who showed that feeding a low-protein diet to laying hens did not influence shell and internal egg quality measures. The period effect was not sig-
Table 4. Effects of dietary treatments on FCR throughout the experiment1 Month 1 (June 2005) 2 (July 2005) 3 (August 2005) 4 (September 2005) 5 (October 2005) 6 (November 2005) 7 (December 2005) 8 (January 2006) 9 (February 2006) 10 (March 2006) 11 (April 2006) 12 (May 2006) 1
Each treatment consisted of 13 replicates. *Significant (P < 0.05).
Control
Reduced-CP
P-value
3.59 ± 0.16 1.88 ± 0.02 1.79 ± 0.02 1.78 ± 0.02 1.90 ± 0.03 1.90 ± 0.03 1.99 ± 0.03 1.96 ± 0.03 2.11 ± 0.04 2.25 ± 0.05 2.33 ± 0.06 2.38 ± 0.06
3.89 ± 0.29 1.86 ± 0.03 1.74 ± 0.03 1.79 ± 0.04 1.90 ± 0.03 1.93 ± 0.03 1.99 ± 0.03 1.99 ± 0.03 2.19 ± 0.04 2.39 ± 0.03 2.50 ± 0.06 2.57 ± 0.08
0.379 0.639 0.242 0.913 0.674 0.471 0.762 0.589 0.248 0.036* 0.050* 0.081
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1 (June 2005) 2 (July 2005) 3 (August 2005) 4 (September 2005) 5 (October 2005) 6 (November 2005) 7 (December 2005) 8 (January 2006) 9 (February 2006) 10 (March 2006) 11 (April 2006) 12 (May 2006)
Control
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Missed 0.014* 0.750 0.591 0.550
Low-protein
Missed 3.58 ± 0.12 3.29 ± 0.18 3.46 ± 0.16 3.26 ± 0.12
Control
Missed 3.01 ± 0.18 3.19 ± 0.42 3.35 ± 0.52 3.36 ± 0.11
CONCLUSIONS AND APPLICATIONS
0.226 0.928 0.746 0.071 0.881 0.38 ± 0.01 0.38 ± 0.01 0.40 ± 0.01 0.38 ± 0.01 0.39 ± 0.01 0.326 0.828 0.912 0.106 0.830 1
Each treatment consisted of 13 replicates. *Significant (P < 0.05).
4.76 ± 0.34 5.85 ± 0.27 4.48 ± 0.31 4.45 ± 0.35 5.36 ± 0.54 5.26 ± 0.36 5.92 ± 0.16 4.43 ± 0.31 4.35 ± 0.42 5.53 ± 0.57 Prepeak Peak 3 mo postpeak 6 mo postpeak 9 mo postpeak
1. Layer performance is satisfactory on reduced-protein diets for short periods. 2. Long-term feeding of reduced-protein diets will drop the performance in the late stage of production, even though no amino acids are limiting and the TSAA:Lys ratio is the same. This may be due to the gradual depletion of body protein reserves in birds on the reducedCP diet. 3. We recommend that the rotational use of reduced-protein diets during a production cycle be studied.
REFERENCES AND NOTES
0.39 ± 0.01 0.39 ± 0.01 0.40 ± 0.01 0.40 ± 0.02 0.39 ± 0.01
P-value
Low-protein Period
Control
Low-protein
P-value
Control
Shell thickness (mm) Albumen height (mm)
Table 5. Effects of dietary treatments on albumen height, shell thickness, and shell strength during different stages of the experiment1
nificant for shell thickness and strength but was significant for albumen height. Albumen height of eggs at 3 and 6 mo postpeak was surprisingly reduced.
1. Austic, R. E. 1981. On the nature of amino acid interactions. Pages 5–13 in Proc. Cornell Nutr. Conf. for Feed Manufact. Cornell University, Ithaca, NY. 2. Ishibashi, T., and C. Yonemochi. 2003. Amino acid nutrition in egg production industry . Anim. Sci. J. 74:457– 469. 3. Keshavarz, K. 1984. The effect of different dietary protein levels in the rearing and laying period on performance of White Leghorn chickens. Poult. Sci. 63:2229– 2240. 4. Hsu, J. C., C. Y. Lin, and P. W. Chiou. 1998. Effects of ambient temperature and methionine supplementation of a low-protein diet on the performance of laying hens. Anim. Feed Sci. Technol. 74:289–299. 5. Blair, R., J. P. Jacob, S. Ibrahim, and P. A. Wang. 1999. Quantitative assessment of reduced-protein diets and supplements to improve nitrogen utilization. J. Appl. Poult. Res. 8:25–47. 6. Junqueira, O. M., A. C. de Laurentiz, R. da Silva Filardi, E. A. Rodrigues, and E. M. Casartelli. 2006. Effects of energy and protein levels on egg quality and performance of laying hens at early second production cycle. J. Appl. Poult. Res. 15:110–115. 7. National Research Council. 1994. Nutrient Requirements for Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC. 8. Hy-Line International. Hy-Line W36 Commercial Management Guide, Hy-Line Int. USA. 2005. 9. Association of Official Analytical Chemists. 1990. Methods of Analysis. 15th ed. AOAC, Arlington, VA. 10. Andrew, R. P., and N. A. Baldar. 1985. Amino acid analysis of feed constituents. Science Tools. 32:44–48. 11. Pharmacia Biotech (Biochrom) Ltd., Cambridge, UK.
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Shell strength (kg/cm2)
P-value
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18. Roberts, S. A., H. Xin, B. J. Kerr, J. R. Russell, and K. Bregendahl. 2007. Effects of dietary fiber and reduced crude protein on nitrogen balance and egg production in laying hens. Poult. Sci. 86:1716–1725. 19. Sohail, S. S., M. M. Bryant, and D. A. Roland. 2002. Influence of supplemental lysine, isoleucine, threonine, tryptophan and total sulfur amino acids on egg weight of Hy-Line W-36 hens . Poult. Sci. 81:1038–1044. 20. Wu, G., P. Gunawardana, M. M. Bryant, R. A. Voitle, and D. A. Roland. 2007. Effects of dietary energy and protein on performance, egg composition, egg solids, egg quality and profits of Hy-line W-36 hens during phase 3. Jpn. Poult. Sci. 44:52–57. 21. Khajali, F., M. Faraji, and S. Karimi Dehkordi. 2007. Effects of reduced-protein diets at constant total sulfur amino acids:lysine ratio on pullet development and subsequent laying hen performance. Am. J. Anim. Vet. Sci. 2:89–92.
Downloaded from http://japr.oxfordjournals.org/ at University of Otago Science Library on December 21, 2014
12. Moore, S., and W. H. Stain. 1963. Chromatographic determination of amino acids by the use of automatic recording equipment. Methods Enzymol. 6:819–831. 13. SAS Institute. 1997. SAS User’s Guide. SAS Inst. Inc., Cary, NC. 14. Koelkebeck, K. W., C. W. Parsons, R. W. Leeper, and X. Wang. 1993. Effect of supplementation of a low-protein corn molt diet with amino acids on early postmolt laying hen performance. Poult. Sci. 72:1528–1536. 15. Novak, C., H. M. Yakout, and E. Schedeler. 2006. The effect of dietary protein level and total amino acid:lysine ratio on egg production parameters and egg yield in Hy-Line W-98 hens. Poult. Sci. 85:2195–2206. 16. Keshavarz, K., and R. E. Austic. 2004. The use of low-protein, low-phosphorous, amino acid-, and phytasesupplemented diets on laying hen performance and nitrogen and phosphorous excretion . Poult. Sci. 83:75–83. 17. Leeson, S., and L. J. Caston. 1996. Response of laying hens to diets varying in crude protein or available phosphorous. J. Appl. Poult. Res. 5:289–296.
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