Influence of Added Synthetic Lysine in Low-Protein Diets with the Methionine Plus Cysteine to Lysine Ratio Maintained at 0.75

2005 Poultry Science Association, Inc.

Influence of Added Synthetic Lysine in Low-Protein Diets with the Methionine Plus Cysteine to Lysine Ratio Maintained at 0.75 Department of Poultry Science, Auburn University, Auburn, Alabama 36849

Primary Audience: Nutritionists, Egg Producers, Researchers, Feed Manufacturers SUMMARY Two studies were conducted to determine the influence of added synthetic lysine to low-protein diets. The purpose of experiment 1 was to determine the correct Met+Cys/Lys ratio in low-protein diets. The objective of experiment 2 was to determine the influence of added synthetic lysine in low-protein diets with the Met+Cys/Lys ratio maintained at 0.75. In both experiments, there were 8 replicates per treatment with 15 Hy-Line W-36 hens (37 wk old) in each replicate. Experiment 1 had 4 Met+Cys/Lys ratios (0.75, 0.80, 0.85, and 0.90), and experiment 2 was a 2 × 4 factorial arrangement of treatments with 2 protein levels (14.3 and 13.6%) and 4 added synthetic lysine levels (0.000, 0.025, 0.050, and 0.075%). The results of experiment 1 showed no difference (P > 0.05) in performance among 4 Met+Cys/Lys ratios from 0.75 to 0.90, indicating a Met+Cys/Lys ratio of 0.75 was adequate. The results of experiment 2 showed that beneficial effects (P < 0.05) of added synthetic lysine were obtained for feed consumption, egg production, egg mass and egg weight at 13.6% protein level, and for feed conversion at 14.3% protein level, indicating that the quality of low-protein diet can be improved by added lysine when the Met+Cys/Lys ratio is maintained at 0.75. Key words: layer, lysine, methionine, protein, ratio 2005 J. Appl. Poult. Res. 14:174–182

DESCRIPTION OF PROBLEM Low-protein diets are used for 3 major reasons. First, the same quantity of amino acid intake can be maintained with a low-protein level diet as feed intake increases due to environmental temperature [1]. Second, egg mass decreases as hen age increases, and this reduces the need for protein. Third, low-protein diets are a way to reduce nitrogen excretion [2, 3, 1

4, 5]. Therefore, interest is growing in studying minimum dietary protein and amino acid levels to optimize poultry production and maximize efficiency of protein use. However, the quality of protein in low-protein diets may not be as good as that in highprotein diets, because the amino acid mixture in low-protein diets may not be as balanced as that in high-protein diets. The reason may be due to deficiencies of more than 1 amino acid,

Current address: Jean Mayer, USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111. To whom correspondence should be addressed: [email protected].

2

Downloaded from http://japr.oxfordjournals.org/ at California Institute of Technology on May 28, 2015

Z. Liu,1 G. Wu, M. M. Bryant, and D. A. Roland, Sr.2

LIU ET AL.: METHIONINE + CYSTEINE PER LYSINE RATIO

MATERIALS AND METHODS The basal diets in both experiments were formulated to meet the commercial management guide of nutrient requirements for HyLine Variety W-36 [10], with the exception of total protein. The diets were formulated based on lysine but not protein. It would be desirable to hold lysine and protein from natural ingredients constant, but this cannot be accomplished with only corn and soybean. Therefore, the protein level is allowed to float while holding lysine from corn and soybean constant. To ensure the diets were properly mixed, the diets were analyzed for amino acid composition. The dietary analysis confirmed the experiment was conducted as expected (Table 1). In experiment 1, there were 4 Met+Cys/Lys ratio (0.75, 0.80, 0.85, and 0.90). The lysine level was held at 0.825% with an average 15.4% protein (calculated). In experiment 2, a 2 × 4 factorial arrangement was used with 2 low-protein levels (13.6 and 14.3%) and 4 added synthetic lysine levels (0.000, 0.025, 0.050, and 0.075%) (Table 2). In both experiments, Hy-Line W-36 hens [10] (37 wk old) were used. Three hens were

housed in a 40.6- × 45.7-cm cage, and a replicate consisted of 5 adjoining cages. Thirty-two groups were randomly assigned to 4 dietary treatments in experiment 1, and 64 groups were randomly assigned to 8 dietary treatments in experiment 2. Replicates were equally distributed into upper and lower cage levels to minimize cage level effect. All hens were housed in an environmentally controlled house with temperature maintained at approximately 20°C to allow for high feed consumption. The house had controlled ventilation and lighting (16 h/ d) but no control on relative humidity. All hens were supplied with feed and water ad libitum. Feed consumption was recorded weekly, egg production was recorded daily, egg weight was determined biweekly, and egg specific gravity was determined monthly. Egg weight and egg specific gravity were measured, using all eggs produced during 2 consecutive days. Egg specific gravity was determined by the flotation method [11]. Mortality was recorded daily, and calculation of feed consumption was adjusted accordingly. Body weight was obtained by weighing 4 hens per replicate at the end of the experiment. Egg mass and feed conversion (g of feed/g of egg) were calculated from egg production, egg weight, and feed consumption. Egg component percentages and egg solid contents were measured at the end of the experiments as described by Fletcher et al. [12] and Prochaska et al. [13]. Three eggs from every replicate were collected at the end of the experiment for measuring the component percentage of yolk, albumen and shell, and the solid content of total, yolk, and albumen. There were 4 replicates with 3 eggs per replicate in each treatment of component percentage and total solid measurement. Yolk and albumen were manually separated. Albumen weight was calculated by subtracting the weight of yolk and shell from the whole egg weight. The yolk and albumen were mixed completely, and 5 to 6 g of homogenate was pipetted into an aluminum dish with weight recorded to 0.0001 g. The sample was dried in an oven for 24 h at 105°C [14], removed from the oven, and then weighed. Four replicates with another 3 eggs per replicate in each treatment were used to measure the yolk and albumen solid content. After separating, albumen and yolk were

Downloaded from http://japr.oxfordjournals.org/ at California Institute of Technology on May 28, 2015

but lysine may be largely responsible. For example, when decreasing protein from 19.0 to 14.2% in a corn-soybean diet, the methionine content decreases from 0.28 to 0.24%; however, the lysine content decreases from 0.92 to 0.69%. Because the lysine level drops 5 times more than the methionine level in corn-soybean diets, the addition of lysine in low-protein cornsoybean diets may improve the protein quality. However, most corn-soybean diets for layers do not contain synthetic lysine. From previous studies [6, 7, 8] in our laboratory, we believe the optimal Met+Cys/Lys ratio for laying hens is 0.75, which is lower than the implied value in NRC [9]. Therefore, the purpose of the first experiment (with dietary lysine level of 0.82%) was to confirm if the optimal performances and profits could be obtained with a Met+Cys/Lys ratio of 0.75. The objective of the second experiment was to determine if the quality of low-protein corn-soybean diets could be improved by adding synthetic lysine while maintaining a constant Met+Cys/Lys ratio of 0.75.

175

15.40 2,863 4.00 0.59 0.40 0.39 0.66 0.82 0.18

15.63 0.38 0.65 0.87

15.43 0.34 0.60 0.82

67.40 19.69 5.07 4.00 1.63 1.09 0.41 0.25 0.25 0.134 0.075

Diet 2

15.38 2,863 4.00 0.59 0.40 0.35 0.62 0.82 0.18

67.45 19.69 5.06 4.00 1.63 1.09 0.41 0.25 0.25 0.093 0.075

Diet 1

15.00 0.41 0.68 0.85

15.42 2,863 4.00 0.59 0.40 0.43 0.70 0.82 0.18

67.36 19.70 5.07 4.00 1.63 1.09 0.41 0.25 0.25 0.176 0.075

Diet 3

Experiment 1

15.04 0.46 0.72 0.84

15.44 2,863 4.00 0.59 0.40 0.47 0.74 0.82 0.18

67.31 19.70 5.07 4.00 1.63 1.09 0.41 0.25 0.25 0.218 0.075

Diet 4

13.71 0.25 0.50 0.67

14.17 2,863 4.00 0.58 0.40 0.26 0.52 0.69 0.16

71.08 16.77 5.08 4.00 1.64 0.51 0.41 0.25 0.25 0.017 0.000

Diet 1

13.81 0.27 0.53 0.74

14.28 2,863 4.00 0.58 0.40 0.28 0.54 0.71 0.16

70.79 16.98 5.07 4.00 1.64 0.55 0.41 0.25 0.25 0.034 0.025

Diet 2

13.31 0.28 0.52 0.73

14.39 2,863 4.00 0.58 0.40 0.30 0.55 0.74 0.16

70.51 17.18 5.07 4.00 1.64 0.59 0.41 0.25 0.25 0.051 0.050

Diet 3

14.37 0.30 0.55 0.75

14.49 2,863 4.00 0.58 0.40 0.31 0.57 0.76 0.16

70.23 17.38 5.07 4.00 1.64 0.63 0.41 0.25 0.25 0.068 0.075

Diet 4

12.24 0.22 0.45 0.63

13.42 2,863 4.00 0.58 0.40 0.24 0.48 0.63 0.14

73.45 14.80 5.08 4.00 1.65 0.11 0.41 0.25 0.25 0.000 0.000

Diet 5

Experiment 2

Downloaded from http://japr.oxfordjournals.org/ at California Institute of Technology on May 28, 2015

13.63 2,863 4.00 0.58 0.40 0.27 0.51 0.69 0.15 12.83 0.25 0.48 0.70

13.10 0.23 0.48 0.67

72.89 15.21 5.08 4.00 1.65 0.19 0.41 0.25 0.25 0.030 0.050

Diet 7

13.53 2,863 4.00 0.58 0.40 0.25 0.49 0.66 0.14

73.17 15.00 5.08 4.00 1.65 0.15 0.41 0.25 0.25 0.013 0.025

Diet 6

13.35 0.27 0.52 0.73

13.74 2,863 4.00 0.58 0.40 0.29 0.53 0.71 0.15

72.61 15.41 5.08 4.00 1.65 0.23 0.41 0.25 0.25 0.048 0.075

Diet 8

Provided per kilogram of diet: vitamin A (as retinyl acetate), 8,000 IU; cholecalciferol, 2,200 ICU; vitamin E (as DL-α-tocopheryl acetate), 8 IU; vitamin B12, 0.02 mg; riboflavin, 5.5 mg; D-calcium pantothenic acid, 13 mg; niacin, 36 mg; choline, 50 mg; folic acid, 0.5 mg; vitamin B1 (thiamin mononitrate), 1 mg; pyridoxine, 2.2 mg; D-biotin, 0.05 mg; vitamin K (menadione sodium bisulfate complex), 2 mg. 2 Provided per kilogram of diet: manganous oxide, 65 mg; iodine (ethylene diamine dihydriodide), 1 mg; ferrous carbonate, 55 mg; copper oxide, 6 mg; zinc oxide, 55 mg; sodium selenite, 0.3 mg. 3 DL-Met calculated as 99.7%. 4 L-Lys calculated as 78.6%.

1

Corn Soybean meal Limestone Hard shell Dicalcium phosphate Poultry oil NaCl Vitamin premix1 Mineral premix2 3 DL-Met 4 L-Lys Calculated analysis Crude protein ME, kcal/kg Ca Total phosphorus Available phosphorus Methionine Met + Cys Lys Trp Experimental analysis Crude protein Met Met + Cys Lys

Diet 1

TABLE 1. Ingredients of the diets

176

JAPR: Review Article

LIU ET AL.: METHIONINE + CYSTEINE PER LYSINE RATIO

177

TABLE 2. Experiment design (formulated based on lysine)

Diet

Added Lys1 (kg/ton)

Natural Lys %

Total Lys (%)

Added Met (%)

Added Met (kg/ton)

Natural Met (%)

Met + Cys (%)

Met + Cys/ Lys ratio

0.075 0.075 0.075 0.075

1.50 1.50 1.50 1.50

0.766 0.766 0.766 0.766

0.825 0.825 0.825 0.825

0.093 0.134 0.176 0.218

1.86 2.68 3.52 4.36

0.35 0.39 0.43 0.47

0.619 0.660 0.701 0.743

0.75 0.80 0.85 0.90

0.000 0.025 0.050 0.075 0.000 0.025 0.050 0.075

0.00 0.50 1.00 1.50 0.00 0.50 1.00 1.50

0.688 0.688 0.688 0.688 0.635 0.635 0.635 0.635

0.688 0.713 0.738 0.763 0.635 0.660 0.685 0.710

0.017 0.034 0.051 0.068 0.00 0.013 0.030 0.048

0.33 0.77 1.12 1.44 0.00 0.26 0.60 0.96

0.26 0.28 0.30 0.31 0.24 0.25 0.27 0.29

0.516 0.535 0.554 0.572 0.476 0.495 0.514 0.533

0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75

Lys = 78.6% Lys.

1

mixed; the measurement of albumen and yolk solids followed the same procedure as above. Data for all criteria in both experiments were analyzed using general linear model procedure in SAS/STAT [15]. The average means for different Met+Cys/Lys ratio in experiment 1 were separated with a Tukey test.

RESULTS Experiment 1 The Met+Cys/Lys ratio had no influence (P > 0.05) on feed consumption, egg production, egg mass, egg weight, and feed conversion. The average feed consumption, egg production, egg mass, egg weight, and feed conversion were 98.5 g/hen per day, 83%, 50.22 g/hen per day, 60.55 g and 1.98 g of feed per gram of egg, respectively. There were no differences (P > 0.05) in BW, egg specific gravity, and egg composition among the 4 Met+Cys/Lys ratios (data not shown). Experiment 2 Mortality, Feed Consumption, and Feed Conversion. Total mortality in experiment 2 was 0.52% (5 hens out of 960). Mortality was not significantly affected by the treatment (P > 0.05) (data not shown). Calculation of feed consumption was adjusted for mortality. An interaction (P < 0.05) occurred between protein

and added synthetic lysine (Table 3). There was no added lysine effect (P > 0.05) on feed consumption at 14.3% protein level, but there was an added lysine effect (P < 0.01) at 13.6% protein level. No interaction (P > 0.05) between protein and added synthetic lysine in feed conversion existed (Table 3). However, there was an added lysine effect (P < 0.01) on feed conversion at 14.3% protein level (Figure 1), but no added lysine effect (P > 0.05) occurred at 13.6% protein level. There was a protein effect (P < 0.01), and feed conversions were 2.03 g of feed per gram of egg at 14.3% and 2.15 g of feed per gram of egg at 13.6% protein level, respectively. Egg Production, Egg Mass, and Egg Weight. There was no interaction (P > 0.05) between protein and added synthetic lysine level on egg production, egg mass, and egg weight (Table 3). However, when data were separately analyzed for 14.3 and 13.6% protein level, the results showed that there were no added lysine effects (P > 0.05) on egg production, egg mass, and egg weight at 14.3% protein level, but there were beneficial effects (P < 0.05) on them at 13.6% protein level (Figures 2 to 4). There were differences (P < 0.01) in egg production, egg mass, and egg weight; all of them increased as the protein level increased. Body Weight and Egg Specific Gravity. There were no interactions (P > 0.05) between

Downloaded from http://japr.oxfordjournals.org/ at California Institute of Technology on May 28, 2015

Experiment 1 1 2 3 4 Experiment 2 1 2 3 4 5 6 7 8

Added Lys (%)

JAPR: Review Article

178 TABLE 3. Influence of added synthetic lysine on performances Feed consumption (g/hen per day)

Factor Protein (%) Lys (%)

14.3%

SEM Protein Lys Protein × Lys

99.9 97.4 96.7 99.0 98.3 100.5 100.2 100.6 99.0 99.6 93.2 97.3 97.7 101.5 1.4 0.0210 0.0761 0.0265

2.03 2.15 2.12 2.13 2.07 2.05 2.09 2.04 2.03 1.97 2.15 2.23 2.10 2.13 0.04 0.0003 0.1065 0.3161

protein and added synthetic lysine in egg specific gravity or BW (Table 4). No added lysine effect (P > 0.05) on egg specific gravity occurred, but as added lysine increased, BW increased (P = 0.0508). There was also a protein effect (P < 0.05) on both egg specific gravity and BW. As the protein level increased, the

Egg production (%)

82.5 78.0 78.9 79.5 80.4 82.3 81.4 83.3 80.7 84.7 76.3 75.7 80.2 79.8 1.6 Probability 0.0002 0.1746 0.1795

Egg mass (g/hen per day) 49.37 45.58 45.93 46.70 47.95 49.31 48.33 49.47 48.98 50.70 43.53 43.93 46.93 47.92 1.04 <0.0001 0.0107 0.2960

Egg weight (g) 59.76 58.57 58.42 58.71 59.59 59.93 59.48 59.44 60.27 59.84 57.36 57.99 58.91 60.02 0.45 0.0004 0.0035 0.0800

egg specific gravity decreased and the BW increased. Egg Composition. There were no protein and lysine interactions or added lysine effect (P > 0.05) among total egg solid, yolk solid, albumen solid, and percentage of eggshell, yolk, and albumen. There were no protein ef-

FIGURE 1. Influence of added synthetic lysine on feed conversion at different protein levels.

Downloaded from http://japr.oxfordjournals.org/ at California Institute of Technology on May 28, 2015

13.6%

14.3 13.6 0.000 0.025 0.050 0.075 0.000% 0.025% 0.050% 0.075% 0.000% 0.025% 0.050% 0.075%

Feed conversion (g of feed/g of egg)

LIU ET AL.: METHIONINE + CYSTEINE PER LYSINE RATIO

179

fects among yolk solid, albumen solid, eggshell percentage, and yolk percentage. But total solid for 14.3% protein level was higher (P < 0.05) than that for 13.6% protein level, and the albumen percentage for 14.3% protein level was higher (P = 0.0517) than for 13.6% protein level (Table 5).

DISCUSSION Some previous studies indicated that the implied ratios in NRC and Hy-Line W-36 management guideline [9, 10] were too high for diets containing a higher lysine or protein level and stated that the correct Met+Cys/Lys ratio

FIGURE 3. Influence of added synthetic lysine on egg mass at different protein levels.

Downloaded from http://japr.oxfordjournals.org/ at California Institute of Technology on May 28, 2015

FIGURE 2. Influence of added synthetic lysine on egg production at different protein levels.

JAPR: Review Article

180

was 0.75 [6, 7, 8]. Many researchers reported that adding synthetic methionine to low-protein diets was economical [16, 17, 18, 19]. The results of experiment 1 showed that there was no response to the increase of TSAA, indicating

a Met+Cys/Lys ratio of 0.75 was also appropriate in these diets containing 0.82% lysine. Synthetic methionine is typically added to all corn-soybean diets, but little or no synthetic lysine is added even though lysine drops much

TABLE 4. Influence of added synthetic lysine on egg specific gravity and BW (kg) Egg specific gravity Factor

Month 1

Month 2

Overall

SEM

1.0801 1.0808 1.0806 1.0801 1.0806 1.0805 1.0799 1.0798 1.0805 1.0803 1.0814 1.0804 1.0808 1.0808 0.0004

1.0783 1.0788 1.0790 1.0785 1.0782 1.0784 1.0784 1.0780 1.0784 1.0783 1.0797 1.0790 1.0780 1.0786 0.0005

1.0792 1.0798 1.0798 1.0793 1.0794 1.0795 1.0791 1.0789 1.0794 1.0793 1.0805 1.0797 1.0794 1.0797 0.0004

1.54 1.52 1.51 1.53 1.54 1.55 1.53 1.55 1.55 1.56 1.49 1.52 1.53 1.55 0.02

Protein Lys Protein × Lys

0.0211 0.6086 0.4961

0.1464 0.4277 0.3757

0.0329 0.5859 0.3386

0.0206 0.0508 0.7652

Protein (%) Lys (%)

14.3%

13.6%

14.3 13.6 0.000 0.025 0.050 0.075 0.000% 0.025% 0.050% 0.075% 0.000% 0.025% 0.050% 0.075%

BW (kg)

Probability

Downloaded from http://japr.oxfordjournals.org/ at California Institute of Technology on May 28, 2015

FIGURE 4. Influence of added synthetic lysine on egg weight at different protein levels.

LIU ET AL.: METHIONINE + CYSTEINE PER LYSINE RATIO

181

TABLE 5. Influence of added synthetic lysine on egg composition Total solids (%)

Factor Protein (%) Lys (%)

14.3%

SEM Protein Lys Protein × Lys

24.71 24.36 24.42 24.74 24.48 24.49 24.47 24.89 24.81 24.67 24.37 24.60 24.16 24.32 0.15 0.0287 0.4621 0.6489

47.92 48.39 48.37 48.08 47.21 48.96 48.51 47.52 46.47 49.19 48.24 48.64 47.96 48.74 0.66 0.4831 0.3267 0.6595

more than methionine when protein level decreases. The results of experiment 2 demonstrated that adding synthetic lysine improved overall hen performance. An economic analysis was also conducted for experiment 2, using the feed and egg prices at the time of this study [20, 21]. Results indicated that the optimal added synthetic lysine level was 0.075% for the 14.3% protein diet and 0.050% for the 13.6% protein diet. These results indicated protein use in low-protein diets could be improved with added synthetic lysine. Eggs are predominantly marketed with the shell, but the percentage of eggs consumed in the form of processed eggs has been increasing over the past 2 decades [13]. Therefore, egg

Albumin solids (%) 12.27 11.90 11.99 11.86 12.59 11.89 12.15 11.99 12.96 11.98 11.84 11.73 12.21 11.81 0.21 Probability 0.0933 0.0799 0.7755

Shell (%) 8.73 8.89 8.74 9.13 8.67 8.70 8.49 9.08 8.54 8.81 8.99 9.19 8.80 8.60 0.13 0.2145 0.0631 0.2885

Yolk (%) 29.27 29.72 29.68 29.46 29.26 29.57 29.41 28.97 28.85 29.87 29.96 29.96 29.67 29.28 0.34 0.2045 0.8398 0.3661

Albumen (%) 62.00 61.39 61.58 61.41 62.07 61.72 62.11 61.96 62.60 61.32 61.05 60.86 61.53 62.13 0.30 0.0517 0.4569 0.0797

component percentage and solid content have attracted interests of nutritionists. No influence (P > 0.05) of Met+Cys/Lys ratio (data not shown) and added synthetic lysine on egg quality was detected in this study, but egg total solid and albumen percentage was higher (P < 0.05) at 14.3% protein level than at 13.6% protein level. There are some studies [22, 23, 24] about the effect of dietary protein on egg quality, but only a few studies were about the effect of individual nutrients. Prochaska reported lysine intake of 1,613 compared with 677 mg/ hen per day significantly increased albumen weight, solids, and protein, but there were no significant differences in yolk weight, protein, and solids [13]. More research is needed on the effects of different nutrients on egg quality.

CONCLUSIONS AND APPLICATIONS 1. There were no effects when methionine was increased to increase Met+Cys/Lys ratio above 0.75 when lysine was formulated at 0.82%. 2. A beneficial effect of added synthetic lysine was obtained for feed consumption, egg production, egg mass, and egg weight at 13.6% protein level, and for feed conversion at 14.3% protein level, indicating that the quality of low-protein diets can be improved by added lysine when the Met+Cys/Lys ratio is maintained at 0.75. 3. No influence of added synthetic lysine on egg quality was detected in this study, but total egg solids and albumen percentage increased as the protein level increased.

Downloaded from http://japr.oxfordjournals.org/ at California Institute of Technology on May 28, 2015

13.6%

14.3 13.6 0.000 0.025 0.050 0.075 0.000% 0.025% 0.050% 0.075% 0.000% 0.025% 0.050% 0.075%

Yolk solids (%)

JAPR: Review Article

182

REFERENCES AND NOTES 1. Harms, R. H. 1981. Specifications of feeding commercial layers based on daily feed intake. Feedstuffs 47:40–41.

14. Association of Official Analytical Chemists. 1984. Official Methods of Analysis. 14th ed. Washington, DC.

2. Jais, C. F. X., and M. Kirchgessner. 1993. Effect of diets with low protein content and supplemented with amino acids on egg production and nitrogen excretion of laying hens. Agribiol. Res. Z. Agrarbiol. Agrikulturchem. Okologie 48:26–38.

15. SAS Institute. 2000. SAS/STAT User’s Guide. SAS Institute Inc., Cary, NC.

3. Summers, J. D. 1993. Reduction of nitrogen excretion of the laying hen by feeding lower crude protein diets. Poult. Sci. 72:1473–1478. 4. Blair, R., J. P. Jacob, S. Ibrahm, and P. Wang. 1999. A quantitative assessment of reduced protein diets and supplements to improve nitrogen. J. Appl. Poult. Res. 8:25–47.

17. Combs, G. F. 1962. The interrelationship of dietary energy and protein in poultry nutrition. Nutrition of Pigs and Poultry. University of Nottingham, 8th Easter School in Agricultural Science. D. Lewis and J. T. Moran, ed. Butterworths, London. 18. Harms, R. H., and R. D. Miles. 1988. Influence of Fermatco on the performance of laying hens when fed different levels of methionine. Poult. Sci. 67:842–844.

6. Bateman, A., M. Bryant, and D. A. Roland, Sr. 2000. Optimal M+C/Lysine ratio for first cycle phase I commercial Leghorns. Poult. Sci. 79(Suppl. 1):92. (Abstr.)

19. Waldroup, P. W., and H. M. Hellwig. 1995. Methionine and total sulfur amino acid requirements influenced by stage of production. J. Appl. Poult. Res. 4:283–292.

7. Yadalam, S. S. 2001. Influence of M+C/L ratio, calcium, phosphorus and phytase on performance and profit of commercial Leghorns. M.S. Thesis, Auburn University, Auburn, AL.

20. Roland, D. A., Sr., M. M. Bryant, J. X. Zhang, D. A. Roland, Jr., S. K. Rao, and J. Self. 1998. Econometric feeding and management 1. Maximizing profits in Hy-Line W-36 hens by optimizing total amino acid intake and environmental temperature. J. Appl. Poult. Res. 7:403–411.

8. Yadalam, S. S., M. M. Bryant, and D. A. Roland, Sr. 2000. Optimal M+C/Lysine ratio for first cycle phase I commercial Leghorns. Poult. Sci. 79(Suppl. 1):92. (Abstr.) 9. National Research Council. 1994. Nutrient Requirement for Poultry. 9th rev. ed. National Academy Press, Washington, DC. 10. Hy-Line International. 2000. Hy-Line Variety W-36 Commercial Management Guide 2000-2001. Hy-Line Int., West Des Moines, IA.

21. Roland, D. A., Sr., M. M. Bryant, J. X. Zhang, D. A. Roland, Jr., S. K. Rao, and J. Self. 2000. Econometric feeding and management of commercial Leghorns: Optimizing profits using new technology. Pages 463–472 in Egg Nutrition and Biotechnology. J. S. Sim, S. Nakai, and W. Guenter, ed. CABI Publishing, CAB Int., Wallingford, UK.

11. Holder, D. P., and M. V. Bradford. 1979. Relationship of specific gravity of chicken eggs to number of cracked eggs and percent shell. Poult. Sci. 58:250–251.

22. Butts, J. N., and F. E. Cunningham. 1972. Effect of dietary protein on selected properties of the egg. Poult. Sci. 51:1726–1734.

12. Fletcher, D. L., W. M. Britton, A. P. Rahn, and S. I. Savage. 1981. The influence of layer flock age on egg component yields and solids content. Poult. Sci. 60:983–987.

23. Gardner, F. A., and L. L. Young. 1972. The influence of dietary protein and energy levels on the protein and lipid content of the hen’s egg. Poult. Sci. 51:994–997.

13. Prochaska, J. F., J. B. Carey, and D. J. Shafer. 1996. The effect of L-lysine intake on egg component yield and composition in laying hens. Poult. Sci. 75:1268–1277.

24. Akbar, M. K., J. S. Gavora, G. W. Friars, and R. S. Gowe. 1983. Composition of eggs by commercial size categories: Effects of genetic group, age, and diet. Poult. Sci. 62:925–933.

Downloaded from http://japr.oxfordjournals.org/ at California Institute of Technology on May 28, 2015

5. Saitoh, M. 2001. The trend of studies on reducing nutrient excretion in poultry and pigs by nutritional approaches. Anim. Sci. J. 72:J177-J199.

16. Johnson, D., Jr., and H. Fisher. 1958. The amino acid requirement of laying hens. Br. J. Nutr. 12:276–285.