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Poult Sci 2006. 85:2195-2206
© 2006 Poultry Science Association
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METABOLISM AND NUTRITION

The Effect of Dietary Protein Level and Total Sulfur Amino Acid:Lysine Ratio on Egg Production Parameters and Egg Yield in Hy-Line W-98 Hens1

C. Novak{dagger}, H. M. Yakout§ and S. E. Scheideler*,2

* Department of Animal Sciences, University of Nebraska, Lincoln 68583; {dagger} Department of Animal and Poultry Science, Virginia Tech, Blacksburg 24061; and § Poultry Production Department, Alexandria University, El-Shatby 21656, Alexandria, Egypt

2 Corresponding author: sscheideler1{at}unl.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
A 3 x 3 treatment arrangement varying in dietary protein and TSAA:Lys was used to evaluate the effect of low-protein diets fed to Hy-Line W-98 laying hens. Phase I was 20 to 43 wk of age with 18.9, 17.0, and 14.4 g of protein/hen per day and 0.97, 0.85, and 0.82 TSAA:Lys, whereas phase II was 44 to 63 wk of age with 16.3, 14.6, and 13.8 g of protein/hen per day and 0.92, 0.82, and 0.72 TSAA:Lys. Egg production and feed consumption decreased from 83.7 to 82.2% and 98.8 to 95.6 g, respectively. Feed efficiency improved from 1.680 to 1.645 g of feed/g of egg mass with decreasing dietary protein. Body weight gain was similar for hens fed high or medium protein diets. In phase II, hens consuming 13.8 g of protein/day had significantly reduced egg weight compared with hens consuming 14.6 or 16.3 g of protein/day. Wet and dry albumen percentage, albumen solids, and albumen and yolk protein percentages were significantly decreased with feeding low-protein diets. Yolk protein percentage was increased from 14.85 to 15.11% when decreasing the ratio from 0.97 to 0.82. Hens consuming a low-protein diet produced eggs with the lowest specific gravity. An interaction was observed for protein retention during phase I, feeding 14.4 g of protein/day or a ratio of 0.97 improved protein retention by 9 and 16%, respectively. Overall, hens consuming 16.3 or 14.6 g of protein/hen per day performed similar to hens consuming 18.9 and 17.0 g of protein/hen per day during P1 and P2, respectively. Also, hens consuming diets containing 0.97 and 0.92 TSAA:Lys produced eggs with improved shell quality as compared with other ratios during P1 and P2, respectively.

Key Words: protein • ratio • egg mass • albumen and yolk protein • protein digestibility


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Increased concern over the impact of modern poultry production systems on the environment (N pollution) has led to manipulation of our current diet formulations to decrease the level of N being excreted in the excreta. Because chickens can only utilize about 40% of the dietary protein, it seems logical to decrease the level of protein in the diet (Lopez and Leeson, 1995). To do so, synthetic amino acids must be used to meet the requirements of limiting amino acids due to the dilution of amino acids as the dietary protein is reduced. An ideal protein diet is one way to reduce dietary protein, in turn decreasing fecal N while maintaining egg production parameters. Formulation of diets with the ideal levels of amino acids and limited excess or deficiencies and little of the amino acid being used as energy (ideal protein concept) may help decrease the cost of feed and reduce environmental N pollution.

There has been considerable work with ideal protein concept in turkeys (Boling and Firman, 1997), broilers (Baker, 1997; Knowles and Southern, 1998; Mack et al., 1999), and pigs (Tuitoek et al., 1997; Yen et al., 2005) to determine the optimal level and the proper ratio of each limiting amino acid on a retention basis to diminish interactions between amino acids and excessive feeding of amino acids. In laying hens, there is limited research in this regard. Shafer et al. (1996) reported an optimal diet for Dekalb Delta layers at 52 wk of age supplied a TSAA:Lys of around 0.85, which is similar to that reported by Novak and Scheideler (1998) in Dekalb Delta hens from 40 to 60 wk of age. Novak et al. (2004) reported a TSAA:Lys of 0.71 for optimal egg production parameters and egg yield in early-producing Dekalb Delta hens.

Due to the direct relationship between dietary protein level and N excretion (Lopez and Leeson, 1995), the logical solution to excessive excreta N is to reduce protein content in the diet. Many researchers have been successful in reducing N excretion by reducing the CP content in the diet with and without supplemental amino acids (Schutte et al., 1992; Summers, 1993; Jamroz et al., 1996; Blair et al., 1999) but with mixed effects on production variables. Penz and Jensen (1991) reported decreased egg weights, BW, albumen, and yolk percentages and poorer feed conversion in Dekalb XL hens from 28 to 34 wk of age when fed low-protein diets (13% protein) supplemented with Lys, Met, or Trp individually or in combination at a level 20% above the NRC recommendations and a low-protein diet supplemented with amino N supplying amino acids (Gly and Glu) to equal the 16% protein diet in total N. Keshavarz and Jackson (1992) fed a low-protein diet supplemented with amino acids, which performed equivalent to a positive control in some, but not all, performance traits. During the trial, all production parameters were increased by supplementing the negative control regimen of all 3 dietary protein (14, 13, and 12% protein diet without supplemental amino acids). Summers et al. (1991) reported a reduction in egg mass of 11% from hens consuming a 10% protein diet supplemented with Lys, Met, Arg, and Trp at NRC recommendations compared with a high-protein diet (17%). In contrast, Harms and Russell (1993) reported similar production including egg mass when supplying hens with a low-protein diet (15 or 13% dietary protein at 28 or 29 wk of age) compared with a control diet (17.6 or 15.5% dietary protein) during heat stress. The aforementioned research suggests that supplementing low-protein diets with amino acids is dependent on the percentage of dietary CP and parameters evaluated. Thus, the objective of the following research was to evaluate low-protein diets combined with TSAA:Lys on production traits and egg yield, which would positively maximize hens’ production parameters.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
A total of 432 hens (Hy-Line W-98) were randomly assigned to 1 of 9 dietary treatment groups varying in protein and TSAA:Lys. Each of the 9 treatments was assigned to 8 replicate cages with 6 hens per cage. Hens were raised in a commercial facility from hatch to 16 wk of age. They then were placed in layer cages at the University of Nebraska-Lincoln Research Farm and fed a diet formulated to meet nutrient requirements recommended commercially (Hy-Line International, 2004–2006). Hens were housed in an environmentally controlled room (72 to 74°C) with feed and water provided for ad libitum consumption. Hens were maintained on a 16L:8D throughout the trial. Cage dimensions were 50 x 40 cm, equaling 2,000 cm2 of floor space. With 6 hens per cage, each bird had approximately 334 cm2 of floor space. The research was conducted under the approval of the University of Nebraska’s Animal Care Committee. A phase feeding program (phase I: 20 to 43 wk of age; phase II: 44 to 63 wk of age) was used during the experiment from 20 to 63 wk of age. Diets (Tables 1Go and 2Go—phase I and II) were formulated based on feed consumption and age of birds. Recommendations for dietary nutrients were based on the Hy-Line W-98 breeder guide (Hy-Line International, 2004–2006). All protein containing feeding stuffs was analyzed for protein (988.05), ether extract (991.36), and DM (934.01) before formulation (Association of Official Analytical Chemists, 1995), and utilizing regression equations (amino acid prediction model, Degussa Laboratories, Allendale, NJ), amino acid content was determined. Diets were subsequently formulated on an available amino acid basis. The experiment consisted of a 3 x 3 factorial arrangement of treatments. During phase I, there were 3 levels of dietary protein (calculated: 18, 16, and 14%; actual: 19.61, 17.71, and 14.77%) and 3 TSAA:Lys (calculated: 0.91, 0.81, or 0.71; actual: 0.97, 0.85, or 0.82). During phase II, the dietary protein was lowered to 16, 14.5, and 13% (actual: 15.69, 15.50, and 14.25% protein) while maintaining TSAA:Lys (predicted: 0.91, 0.81, and 0.71; actual: 0.92, 0.82, and 0.72). Methionine was supplied in excess of the NRC (1994) requirement to achieve the TSAA:Lys desired.


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  		Table 1. Phase I experimental diets for laying hens fed different dietary protein levels and TSAA:Lys ratios
 

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  		Table 2. Phase II experimental diets for laying hens fed different dietary protein levels and TSAA:Lys
 
Feed samples were collected for each phase of feeding and were subsequently ground using a 1-mm screen Tecator cyclotec grinder (1093 Sample Mill, Tecator, Hoganas, Sweden). All diets were analyzed for Ca (927.02) and P (965.17) and protein (988.05) according to the Association of Official Analytical Chemists (1995). Amino acids were also determined in complete feed rations by Degussa Laboratories utilizing the performic acid oxidation method (994.12).

Feed consumption and egg production were recorded daily on a cage basis, whereas BW were obtained individually on a monthly basis. Body weight gain for each phase and overall was also calculated. Feather scoring was done at the conclusion of the trial utilizing the method of Adams et al. (1977). Weekly, 1-d egg production was used for measuring egg weight. Egg mass was then calculated (egg weight x egg production). Every 2 wk, specific gravities were determined using 1-d egg production from a cage, and 2 eggs per cage were either used for Haugh unit or wet and dry egg component determinations. Specific gravities and egg component measurements were done on alternating weeks. In addition to the above shell-quality test, shell breaking strengths were measured using an Instron instrument (model no. 55R1123, Instron Corp., Canton, MA) every other week during the second phase of the trial. Every 5 wk starting at 20 wk of age until the end of the trial, protein content in fresh yolk and albumen were measured individually in 3 eggs per treatment. The individual components were analyzed for N by Kjeldahl procedures (988.05; Association of Official Analytical Chemists, 1995) and subsequently used to calculate protein values.

At 39 and 59 wk of age, a retention trial was conducted to determine percentage of protein retained using chromic oxide as a marker. Chromic oxide was added at a rate of 0.3% of the diet and fed for 5 d. Starting the third day of marker inclusion, 3 d of manure production was randomly sampled from each cage and collected in aluminum pans, frozen (–20°C), and freeze-dried in a FTS system (Dura Dry; model FD-20-54, FTS Systems Inc., Stone Ridge, NY). Feed samples containing chromic oxide and dried excreta were ground using a 1-mm screen Tecator cyclotec grinder (1093 Sample Mill, Tecator). Ground excreta were sifted (1-mm screen) to remove feathers before analysis. Protein analysis was conducted by Kjeldahl methodology (TecatorKjeltec System, 1003 Distilling Unit, Tecator). Chromic oxide was analyzed by the procedure of Williams et al. (1962) and Perkin-Elmer (1971).

Experimental design for the aforementioned experiment was a randomized complete block design. Blocking was implemented to reduce the effect of lighting as a result of rows. An ANOVA was performed by PROC MIXED procedures (SAS Institute, 1996). Blocks were considered random, whereas protein and TSAA:Lys were fixed. A factorial arrangement of treatments was implemented with 3 levels of protein and 3 TSAA:Lys. Utilizing SAS, mean values for phase I, II, and the entire trial were generated and subsequently analyzed separately to determine differences among treatment means. Linear effects of treatments were also established using contrast statements. The following model was used to determine differences between treatment groups


Formula

where Yijk = variable measured; m = overall mean; Ri = effect as a result of the ith block; aj = effect of the jth level of A; bk = effect of the kth level of B; (ab)jk = interaction effect of the jth level of A and the kth level of B; and eijk = error component. Significance of difference was based on the probability of a type I error set at P ≤ 0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Actual protein and amino acids intake based on feed consumption and diet analysis are presented in Table 3Go. During phase I, protein intake was slightly higher than expected but within expectations. The TSAA:Lys in phase I diets were not as calculated as a result of fluctuating ingredients at the feed mill, which may have affected some of our responses. Phase II was very close to the calculated values.


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  		Table 3. Feed consumption, protein,1 and amino acid intake (actual by diets within phases) of laying hens fed different dietary protein levels and TSAA:Lys1,2
 
Overall, feed consumption (Table 4Go) linearly decreased as protein intake decreased (P < 0.02). Phase I (P < 0.02) and II (P < 0.01) showed a similar response to decreasing protein intake. Also during phase II, there was a protein by ratio interaction (P < 0.05), with hens consuming less feed when fed 13.8 g of protein/hen per day combined with the 0.92 ratio compared with the other TSAA:Lys. Overall, hens consuming high and medium protein intake produced significantly higher than those consuming the lowest protein. Although feed consumption and egg production were affected by protein intake, hens consuming the medium- and high-protein diets performed similarly during the trial.


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  		Table 4. Performance parameters of laying hens fed different dietary protein levels and TSAA:Lys1
 
Feed efficiency (Table 4Go) was significantly affected by protein intake during phase I (P < 0.02). As protein intake decreased, there was a linear improvement in feed efficiency from 1.611 to 1.567 g of feed/g of egg mass. Feed efficiency was similar for hens consuming the medium-and high-protein diets.

Body weight gain (Table 4Go) was affected by protein intake only during phase II (P < 0.01) and overall (P < 0.01). As protein intake was decreased from 16.3 to 13.8 g/hen per day, there was a linear (P < 0.01) decrease in hen weight gain from 90.7 to 22.3 g during phase II. The same negative linear effect (P < 0.01) of decreasing protein intake in overall BW gain was also noted. Hens consuming the medium- and high-protein diets had similar gain during the study.

Egg weights were unaffected (P < 0.06) by protein intake during phase II and overall, but eggs were heavier from hens fed the 2 higher levels of protein (Table 5Go). Overall, egg mass (Table 5Go) was affected by protein intake (P < 0.0001), and a protein x ratio interaction (P < 0.03) was noted. Hens consuming high or medium protein combined with high or medium ratios had similar egg mass. As the level of protein decreased in the diet, egg mass linearly decreased during phase II (P < 0.0001) and overall (P < 0.0001). Hens consuming 14.6 and 16.3 g of protein per day produced an egg mass of 52.3 vs. 52.2 g, respectively, during phase II. Also during phase II, increasing the TSAA:Lys negatively affected (P < 0.06) egg mass.


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  		Table 5. Egg weight and egg mass of laying hens fed different dietary protein levels and TSAA:Lys1
 
Protein intake during phase II and overall had a similar influence on wet and dry albumen percentage and albumen solids (Table 6Go). Wet albumen percentage decreased linearly (P < 0.01) during phase II from 60.3 to 59.7% as protein intake decreased from 16.3 to 13.8 g/hen per day. Dry albumen (Table 6Go) and yolk (Table 7Go) significantly decreased and increased linearly, respectively, as protein intake decreased. When hens were fed either high- or medium-protein diets, albumen percentages were similar. Percentage of albumen protein (Table 6Go) was affected by only protein intake. Albumen protein decreased linearly by reducing protein intake during phase I (P < 0.05) and II (P < 0.01). Albumen protein decreased from 10.37 to 9.67% when feeding the high-and low-protein diets, respectively. Albumen protein was similar in eggs from hens supplied high- and medium-protein diets. During phase II, reducing protein intake linearly reduced Haugh units. Dietary effects on Haugh units during phase I and overall were nonsignificant.


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  		Table 6. Albumen parameters of laying hens fed different dietary protein levels and TSAA:Lys1
 

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  		Table 7. Yolk parameters of laying hens fed different dietary protein levels and TSAA:Lys1
 
Protein intake influenced yolk component (Table 7Go). Percentage of wet yolk was linearly increased (P < 0.05) during phase II. As protein intake was decreased from 16.3 to 13.8 g/day, there was a linear increase in percentage of yolk from 27.0 to 27.4%, respectively. Effect of increasing protein intake on dry yolk values was similar as wet. Percentage of yolk protein (Table 7Go) was linearly affected by protein intake (P < 0.003) and ratio (P < 0.03) during phase I. As protein intake decreased from 18.9 to 14.4 g/hen per day, there was a subsequent decrease of 0.4% in yolk protein. As TSAA:Lys ratio was increased from 0.82 to 0.97, percentage of yolk protein decreased linearly.

Wet shell percentage was influenced by protein intake (P < 0.04) during phase II (Table 8Go). Hens consuming the 13.8 g of protein/h per day produced eggs with more shell than those consuming the 14.6 and 16.3 g of protein/h per day, which were similar. During phase I, there was a ratio main effect (P < 0.02). Hens consuming a diet containing a TSAA:Lys of 0.97 produced eggs with a greater percentage of wet shell (12.88%) than hens consuming diets containing 0.85 (12.61%) or 0.82 (12.66%). Percentage of dry shell was affected by ratio during phase I (P < 0.03) and overall (P < 0.01). During phase I, hens consuming the 0.97 ratio diet produced eggs with significantly greater percentage of dry shell (9.63%) compared with hens consuming the 0.85 (9.42%) or 0.82 (9.46%) diets. No effect of protein intake was observed on wet and dry shell percentages. Specific gravity was affected overall (P < 0.01) by protein intake and by ratio (P < 0.01) during phase I. As protein intake decreased, there was a linear (P < 0.001) decrease in overall specific gravity from 1.0829 to 1.0817. Similar significant responses were observed during phase I and II. Eggs produced from hens consuming the medium-and high-protein diets had similar specific gravity. During phase I, eggs produced from hens consuming the 0.97 ratio diet had greater specific gravity (1.0850) compared with hens consuming the 0.85 (1.0839) or 0.82 (1.0844) ratio diets. Dietary treatments had no effect on eggshell breaking strength (Table 8Go).


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  		Table 8. Eggshell quality of laying hens fed different dietary protein levels and TSAA:Lys1
 
During phase I, reducing ratio resulted in a decrease (P < 0.002) in protein retention (Table 9Go) from 41.72 to 35.72 for ratios 0.97 to 0.82, respectively. Also, a significant protein x ratio interaction was noted, during which hens consuming 14.4 mg of CP/d combined with a TSAA:Lys of 0.82 resulted in higher protein retention (46.07%) compared with all other dietary treatments. During phase II, protein intake affected (P < 0.08) protein retention at the intermediate level 16.3 mg/hen per day (47.71%). In phase I, dietary protein reduction resulted in a significant decrease in fecal N (Table 9Go), with the lowest at the lower protein level of 14.4 mg/d (5.12%). Also, a protein by ratio interaction (P < 0.0003) was observed, of which, higher protein (18.9 mg/hen per d) and the intermediate ratio (0.85) had higher fecal N of 6.55%. As protein intake decreased, fecal N was reduced (P < 0.0001), resulting in the lowest N excretion (4.49%) associated with the lowest protein intake of 13.8 mg/d during phase II. The highest protein intake (16.3 mg/hen per d) resulted in higher fecal N values across all TSAA:Lys of 4.98, 4.97, and 4.91 for 0.92, 0.82, and 0.72 ratio, respectively. Feather score was not affected by protein intake or TSAA:Lys.


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  		Table 9. Protein retention, fecal N, and feather score of laying hens fed different dietary protein levels and TSAA:Lys1
 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
In the present study, decreasing protein intake reduced feed consumption by as much as 2 g/hen per day, whereas the medium- and high-protein diets were similar. Feeding low-protein diets has been reported to increase feed consumption in the past. Bartov (1979) reported an increase in feed intake when feeding low-protein diets to chickens, which was explained as the result of an amino acid "appetite" that results when feeding diets marginal in amino acids. Hurwitz et al. (1998) determined this may only be the case for certain amino acids, such as Lys and TSAA, because diets marginal in Arg did not result in an increase in feed intake in growing chickens. In the present study, Lys, TSAA, Thr, and Trp were at or above breeder guide recommendations, which may have satisfied the bird’s appetite for amino acids. Egg production was reduced by as much as 2% during the trial by feeding the lower-protein diet, whereas hens fed the high- and medium-protein diets performed similarly. The effect of low protein intake was more dramatic during the second phase of egg production (43 to 63 wk of age), which may indicate a delayed response to reduced protein intake or amino acids. The reduction in protein or amino acids and energy, due to reduced feed intake, may also have influenced egg production. Harms and Russell (1993) fed a low-protein diet (13%) supplemented with essential amino acids [meeting NRC 1984 recommendations (NRC, 1984)] and reported similar egg production when compared with feeding a diet with 17% protein. This trial was short (6 wk) and may not hold true for the entire production trial. The reduction in egg production may also be the result of interactions among amino acids due to possibly an excessive intake of essential amino acids in the low-protein diets. Also, essential amino acids may be becoming limiting because of their conversion to nonessential amino acids that are in low concentration in low-protein diets. In contrast to the present research, Keshavarz and Jackson (1992) reported similar egg production (18 to 66 wk of age) when using low-protein diets in a phase-feeding program (14, 13, and 12% protein) with supplemental Met, Lys, Trp, and Iso compared with positive control (18, 16.5, and 15% protein). A similar response was reported when utilizing a phase-feeding regimen of 15, 14, and 13% protein diets with adequate Met and Lys. During the present trial, as a result of decreased feed consumption when feeding the low-protein diet, hens were consuming less TSAA than recommended by the Hy-Line W98 breeder guide (Hy-Line International. 2004–2006), which may have contributed to the reduction of egg production during phase II. Results of this trial indicate that reducing protein intake from 18.9 to 17.0 g/hen per day and 16.3 to 14.6 g/hen per day during phase I and II, respectively, with supplemental Lys, Met, Trp, and Thr, maintained egg production. Feed efficiency (g of feed/g of egg mass) was improved as dietary protein decreased. As a result of decreased feed consumption and only a slight decrease in egg weight with decreased protein intake, it was expected that the efficiency would be increased. It is also possible that hens became more efficient in utilizing the dietary protein available. Body weight gain decreased linearly as dietary protein decreased, whereas TSAA:Lys did not influence BW gain. This observation was surprising; because of the role of Lys in tissue protein synthesis, it was expected that the highest TSAA:Lys evaluated would be optimal for maintaining body condition. As the hen ages, the requirement for Lys would decrease and the requirement for TSAA should increase due to their roles in maintenance.

Egg weight was lower when hens consumed less protein (14.4 and 13.8 g/hen per day for phases I and II, respectively) than for the hens consuming greater protein intake. Even with supplemental amino acids (Met, Lys, Trp, and Thr), egg weight was reduced significantly when hens consumed very low-protein diets. It has been reported that even when supplementing certain amino acids, egg weight is reduced due to other marginal amino acids (Penz and Jensen, 1991). A reduction of dietary protein reduces intake of nonessential amino acids such as Glu, Cys, and Gly, which are important N sources. These amino acids may become limiting or essential amino acids may be converted for nonessential purposes, which may result in a limitation of protein (egg) synthesis. Penz and Jensen (1991) reported decreased egg weights when feeding a low-protein diet (13%) supplemented with Lys, Met, or Trp individually or in combination at a level 20% greater than NRC recommendations compared with control-fed hens on a 16% protein diet. Egg mass decreased linearly during the second phase as protein intake decreased. With a combination of low egg production and decreased egg weight, egg mass was decreased in hens fed the lower-protein diets (14.4 and 13.8 g/hen per day). The negative effect of low-protein diets with or without supplemental amino acids on egg mass has also been reported by other researchers (Penz and Jensen, 1991; Summers et al., 1991; Keshavarz and Jackson, 1992). In contrast, Harms and Russell (1993) reported similar responses in egg production parameters, including egg mass, when low-protein diets (15 or 13%) with supplemental Lys, Met, Trp, Arg, Thr, Val, and Ile were compared with high-protein (17.6 or 15.5%) diets.

Egg components were influenced by protein intake but not by the TSAA:Lys. Wet and dry albumen and albumen solid percentages all decreased linearly when protein intake was decreased and were probably one of the factors responsible for the reduction in egg weight. The decrease in percentage of albumen may have been the result of a decrease in albumen synthesis. The lack of response during phase II may have been an indication that the hen had reached its optimal BW and was utilizing amino acids and energy previously used for body growth for egg protein synthesis. The aforementioned response to decreased protein intake is not uncommon and has been reported by others (Hamilton, 1978; Penz and Jensen, 1991; Keshavarz and Jackson, 1992). Penz and Jensen (1991) reported decreases in albumen percentage and increases in yolk percentage as dietary protein decreased from 16 to 13%, whereas Butts and Cunningham (1972) reported differences between chicks consuming 12 and 18% protein on albumen and whole egg solids. Keshavarz and Nakajima (1995) reported an increase in albumen weight and no change in yolk when increasing dietary protein from 17 to 21%. The changes observed may be the result of decreased amino acids available for albumen synthesis (production requirement), but because the yolk is synthesized in the liver, the synthesis for yolk protein synthesis remains constant during dietary protein reduction if the liver preferentially sequestered essential amino acids.

Haugh unit was not affected during phase I or overall but was increased by decreasing dietary protein during phase II. Deaton and Quisenberry (1965), Aitken et al. (1973), and Leeson and Caston (1997) reported similar responses as ours for Haugh units when feeding low-protein diets. In contrast, Hamilton (1978) observed no observable change in Haugh units when feeding low-protein diets to 4 different strains of laying hens.

Shell quality was also affected by protein and ratio, which could potentially have serious consequences for commercial egg-laying operations. Wet shell percentage was increased by decreasing protein intake, whereas low- and high-protein diets were similar during phase II, and all dietary protein treatments were similar during phase I. From this information, hens consuming the low-protein diets may be producing an egg that has more adhering albumen on the shell than the other protein treatments or a smaller egg. Specific gravity was linearly decreased by low-protein diets, indicating that shell quality was being reduced. Although shell breaking strength was not significantly reduced by feeding low-protein diets, shell strength was numerically decreased with reducing protein intake. Increasing the TSAA:Lys increased shell quality, indicating the S amino acid requirement for shell protein matrix synthesis needs to be considered to optimize shell quality. Simkiss and Taylor (1957) reported that the shell protein matrix is comprised of 70% protein. Also, increasing the sulfate groups present in the shell matrix significantly increases the Ca-binding ability, which in turn may increase both shell percentage and specific gravity and overall shell quality. Other researchers have also indicated that decreasing dietary protein will decrease shell quality (Leeson and Caston, 1997; Keshavarz and Nakajima, 1995; Keshavarz and Jackson, 1992).

Protein retention was generally improved when feeding low-protein diets and by increasing the TSAA:Lys from low to high. During phase I, there was a 16% improvement in protein retention when increasing the ratio in the diet from 0.82 to 0.97. The increased improvement in retention indicates that TSAA:Lys is closer to what the hens needed to produce optimally. A 9% improvement in protein retention in combination with the lower protein ratio resulted in 32% less N excreted, which is consistent with Summers (1993), who reported a 40% reduction when feeding a diet containing 11% protein compared with 17%. This decrease could have a positive environmental impact. During the second phase of feeding, protein retention was not significantly affected by dietary protein intake. Hens consuming 13.8 g of protein/h per day gained significantly less weight (22.3 vs. 90.7 g/hen—consuming 16.3 g of protein/d), which may indicate that these hens used less protein per day. It is possible these hens were in a negative N balance state, which reduced any improvement in retention. An improvement of 4% in N retention was noted when dietary protein intake was decreased from 16.3 to 14.6 g/hen per day.

The utilization of low-protein diets for laying hens has considerable ability to reduce N excretion. Reducing protein intake from 18.9 to 17.0 g/hen per day (20 to 43 wk of age) and 16.3 to 14.6 g/hen per day (43 to 63 wk of age) will decrease N excretion without changing the production and egg yield. Also, hens consuming diets containing 0.97 and 0.92 TSAA:Lys produced eggs with improved shell quality as compared with other ratios during P1 and P2, respectively. Further development of an ideal amino acid pattern will be needed to reduce the protein intake further. The implementation of such a diet (ideal protein diet) will require a cost reduction of currently available synthetic amino acids and changes in formulation of the diets to make economically feasible in the field.


   FOOTNOTES
 
1 Published with the approval of the director as page number 15204, Journal Series, Nebraska Agricultural Research Division. Back

Received for publication April 19, 2006. Accepted for publication July 26, 2006.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Adams, A. W., J. V. Craig, and A. L. Bhagwat. 1977. Effects of flock size, age at housing, and mating experience on two strains of egg-type chickens in colony cages. Poult. Sci. 57:48–53.

Aitken, J. R., G. E. Dickerson, and R. S. Gowe. 1973. Effect of intake and source of protein on laying performance of seven strains under single and double cage housing. Poult. Sci. 52:2127–2134.

Association of Official Analytical Chemists. 1995. Official Methods of Analysis. 16th ed. AOAC Int. Washington, DC.

Baker, D. H. 1997 Ideal amino acid profiles for swine and poultry and their applications in feed formulation. Pages 15–18 in Biokyowa Technical Review 9. Biokyowa, Inc., Chesterfield, MO.

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