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J APPL POULT RES 2008. 17:17-33. doi:10.3382/japr.2006-00126
© 2008 Poultry Science Association
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Research Reports

Response to Varying Dietary Energy and Protein With or Without Enzyme Supplementation on Leghorn Performance and Economics. 2. Laying Period

C. L. Novak*,1,2, H. M. Yakout{dagger} and J. Remus{ddagger}

* Department of Animal and Poultry Science, Virginia Tech, Blacksburg 24061; {dagger} Poultry Production Department, Alexandria University, El-Shatby 21545, Alexandria, Egypt; and {ddagger} Danisco Animal Nutrition 411 East Gano, St. Louis, MO 63147

1 Corresponding author: CLNovak{at}landolakes.com


   SUMMARY
TOP
 SUMMARY
DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Commercial laying hens were used to evaluate the use of an enzyme cocktail during their first cycle of lay. Hens were fed 1 of 8 dietary treatments that varied in ME and dietary protein, with or without exogenous enzymes, at an inclusion rate of 0.0375%, from 18 to 60 wk of age. Reducing dietary protein lowered BW gain, egg weight, and egg mass and impaired FCR. In addition, the albumen percentage decreased, whereas the yolk percentage and color increased when feeding lower protein diets. Percentage of energy and protein retention was generally increased by reducing dietary protein. Feeding hens less protein reduced protein digestibility at 60 wk. Dietary ME had little effect on most hen performance parameters. Although reducing ME increased redness of the egg yolk, absolute energy retention was lower when reducing ME overall. Energy digestibility at 60 wk was lower when ME was reduced. Enzyme supplementation reduced egg weight and increased yolk redness during phase A, and reduced egg mass and impaired FCR during phase B. Enzyme supplementation had little effect on energy and protein retention, whereas the response on excreta nitrogen was inconsistent. Excreta nitrogen was lower when feeding hens less protein, thus having a positive impact on the environment. Feeding diets lower in dietary protein or ME reduced the cost of feed, whereas enzyme supplementation increased the overall cost to produce a pound of egg.

Key Words: metabolizable energy • dietary protein • enzyme supplementation • laying hen


   DESCRIPTION OF PROBLEM
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Maintaining or improving laying hen performance, or both, may be achieved by maximizing nutrient utilization from current feedstuffs. Although high egg production and laying efficiency are characteristic of the modern laying hen, reductions in the cost of production and environmental pollution are needed. In the United States, corn and soybean meal are the major ingredients supplying energy and protein in commercial Leghorn diets [1]. As more corn goes to nonagricultural purposes such as ethanol production, it will be important to retain as much energy and protein as possible for the bird to use for production. Soybean meal contains non-digestible carbohydrates, which could be available to hens with proper enzyme supplementation [2]. Wheat makes an excellent replacement for corn in poultry feeds, but dietary modifications are essential because of the nonstarch polysaccharide (NSP) content [3]. The benefits of supplementing NSP-rich poultry diets with exogenous enzymes are well documented [4–7]. Although nutrients in corn are generally considered highly available, a 2 to 3% improvement in feed conversion with enzyme supplementation has been reported [2]. Wheat typically contains 5 to 8% NSP. Xylans are the principal NSP present in wheat, and high levels of dietary inclusion can increase intestinal viscosity. This increase in viscosity can impede digestion and subsequent absorption of nutrients, reducing feed intake and BW gain and impairing FCR [8, 9]. In the poultry feed industry, the use of commercially available exogenous enzymes has greatly increased during the past 15 yr. Supplementing exogenous enzymes can improve the digestion of nutrients from feedstuffs, thereby decreasing feed costs, improving bird performance, and decreasing the environmental impact of land-applied manure [3, 8, 10]. Nitrogen pollution continues to be an issue, and although feeding a reduced CP diet is effective in reducing nitrogen excretion [11, 12], it is not without performance shortfalls [11–14]. The use of an exogenous enzyme cocktail containing a protease may be effective in increasing the digestibility of CP, which is currently 82% [15]. This may in turn increase the availability of nitrogen sources from the diet and improve the performance of Leghorns consuming a low-protein diet.

The current study evaluated the performance and nutrient utilization of White Leghorn hens fed a conventional corn-, soybean meal-, and wheat middlings-based diet lowered in ME or dietary protein, or both, and supplemented with a commercially available enzyme cocktail containing amylase, protease, and xylanase.


   MATERIALS AND METHODS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Animals and Diets
A total of 256 pullets at 18 wk of age were housed at 4 pullets per cage (density 54 in.2/hen). Pullets continued (18 to 60 wk) on similar treatments implemented during the grow-out period and were grouped according to final average BW per treatment [13].

A 2 x 2 x 2 factorial arrangement implementing 2 levels of ME [recommended (RME) [16] vs. a 3% reduction (LME)], dietary CP [recommended (RCP) [16] vs. a 3% point reduction (LCP)], with or without enzyme (EZ) supplementation (added to the basal diets at 0.0375%). Enzyme [17] contained (per g) a guaranteed minimum of 800 units/g of {alpha}-amylase from Bacillus amyloliqufaciens, 8,000 units/g of proteases from Bacillus subtilis, and 600 units/g of β-xylanase from Trichoderma longibrachiatum. Each enzyme had its own activity and definition (and source organism) as follows: xylanase: 1 U was the amount of enzyme that would liberate 0.5 µmol of reducing sugar (expressed as xylose equivalents) from a cross-linked oat spelt xylan substrate at pH 5.3 and 50°C in 1 min; protease: 1 U was the amount of enzyme that would liberate 1 µmol of phenolic compound (tyrosine equivalents) from a casein substrate per minute at pH 7.5 and 40°C; amylase: 1 U was the amount of enzyme that would liberate 1 µmol of glucosidic linkages from a water-insoluble cross-linked starch polymer substrate per minute at pH 6.5 and 37°C. Feed and water were provided for ad libitum consumption.

Starting at 16 wk of age, light was gradually increased from 12 h/d in increments of 30 min/wk to establish a 16L:8D cycle at wk 24. Pullets or hens were housed in an environmentally controlled facility with a daily target temperature of 22°C.

A corn, soybean meal, and wheat middling basal diet (Table 1Go) was formulated to meet Bovans White Leghorn Breeder Guide recommendations [18] for production phases A, B, and C. Production phases were based on egg production changes: phase A: 18 to 38 wk (calculated: RME – 2,871 ME kcal/kg, RCP – 17%; analyzed: 3,706 gross energy kcal/kg, 18.11% CP); phase B: 39 to 50 wk (calculated: RME – 2,871 ME kcal/kg, RCP – 14%; analyzed: 3,766 gross energy kcal/kg, 19.30% CP); and phase C: 51 to 60 wk (calculated: RME – 2,882 ME kcal/kg, RCP – 13.5%; analyzed: 3,777 gross energy kcal/kg, 18.89% CP). Lowered ME, CP, or ME and CP basal diets were formulated and mixed, using the aforementioned diets for each production phase. Each basal diet (n = 4) was then divided in 2, 1 with EZ supplementation and 1 without, totaling 8 dietary treatments.


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  		Table 1. Composition and nutrient content of layer diets (phases A, B, and C) from 18 to 60 wk of age
 
Feed samples, collected from the mixer with a probe during each production phase, were subsequently ground in a 1-mm screened Tecator cyclotec grinder [19] to prepare for analysis. All diets were analyzed for gross energy and protein according to AOAC [20]. In general, nitrogen concentration was determined with a nitrogen analyzer [21] by the combustion method. The equation N x 6.25 was used to convert to CP. Gross energy was determined by bomb calorimetry with a Parr 1261 adiabatic calorimeter [22].

Measurements
From 18 to 60 wk of age, feed intake and FCR (g of feed/g of egg mass) were measured weekly, and egg production and mortality were recorded daily. Starting at 22 wk of age, egg weights were obtained weekly and egg specific gravity every other week. Data were obtained subsequent to gathering a 24-h egg collection according to Strong [23]. Egg mass was calculated weekly (egg production x egg weight). Individual BW were obtained every 4 wk and at phase. Individual hen weights were used to calculate a pen average, with BW gain to loss calculated for each phase and overall. Two eggs per pen were used every other week to determine the effect of diet on egg components (% of wet albumen, yolk, and shell). Yolk color was measured with a Minolta Chroma Meter CR-300 [24] by using the average of 3 readings per yolk (n = 2 yolks/pen). The L value represents lightness (negative toward black, positive toward white), the a value represents red-greenness (negative toward green, positive toward red), and the b value represents the blue-yellow color scale (negative toward blue, positive toward yellow). To analyze the yolk color, the tip of the measuring head was placed against the surface of the yolk.

Excreta were collected from each pen at the end of each phase (38, 50, and 60 wk) to measure protein and energy retention and excreta nitrogen content. At 60 wk of age, all hens were euthanized by cervical dislocation, and ileal contents (from Meckel’s diverticulum to the ileocecal junction) were collected and pooled per pen for analysis of chromium, nitrogen, and energy as described above. Chromic oxide was added to the experimental diets at 3 g/kg (0.3%) as an inert marker. Chromic oxide was analyzed according to Czarnocki et al. [25]. Excreta and ileal samples were frozen and stored at –20°C subsequent to collection until analyzed further. Frozen ileal samples were freeze- dried, whereas frozen excreta samples were thawed, transferred to aluminum pans, and placed in a 65°C oven for 3 d to determine DM. After drying, all samples were ground [19] through a 1-mm screen to prepare them for analysis. Values obtained were used to calculate nutrient retention and ileal digestibility by using the following equation:


Formula

After calculating the percentage of energy and protein retention, the kilocalories of energy and grams of protein per hen per day for each production phase and overall were calculated by using analyzed values for gross energy and CP in diets used in the trial.

Economics were calculated as dollars per pound of egg mass for each production phase and overall (18 to 60 wk of age):


Formula


Formula


Formula

Cost figures began when 50% production was achieved (22 wk of age). All animal procedures were approved by the Virginia Tech Animal Care and Use Committee.

Statistical Analysis
A randomized complete block design was used to reduce the effect of lighting as a result of rows. Analysis of variance was performed by PROC MIXED of SAS [26]. Blocks, ME, CP, and EZ were considered fixed effects. With SAS, average values for each phase were generated and subsequently analyzed separately to determine differences between treatment means established by the LSMEANS statement following a Tukey adjustment. Percentage-based data were transformed by using an arcsine procedure prior to analysis. The following model was used to determine differences between treatment groups:


Formula

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


   RESULTS AND DISCUSSION
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Diet analysis for EZ content proved to be similar to calculated inclusion (data not included). Analyzed dietary CP and gross energy levels in our basal diets were somewhat different from formulated values. Because of the turnover of ingredients at the mill, variation in the nutrients present in raw ingredients may have changed the final nutrient levels. Ingredient ME values used for the formulations were based on NRC 1994 [16].

Hen Performance
Mortality was less than 4.5% during the 40-wk trial and was similar across treatment groups (data not shown). Neither ME nor EZ affected feed intake (Table 2Go). A similar response in feed intake when supplementing a high wheat middling-based diet with Avizyme 1300 has been reported [4]. A reduction in feed intake of 2 g/hen per d has been reported when feeding a diet reduced in CP by 4% points from 20 to 60 wk of age [27]. A similar response was noted in the present trial, but may be misleading as a result of the significant CP x EZ interaction. Without EZ supplementation, varying dietary CP had little effect, whereas when feeding an LCP diet with EZ, feed intake decreased more than without EZ. The opposite was observed when supplementing the RCP diet with EZ. Thus, with EZ supplementation, feed intake of layers fed the LCP diet was significantly lower compared with feeding an RCP diet [1].


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  		Table 2. Effect of dietary energy or protein, with or without enzyme, on feed intake and BW gain from 18 to 60 wk of age
 
Body weight gain was reduced (P ≤ 0.02) by lowering CP during phase B, indicating that the level of CP or amino acids was more important than dietary ME or EZ supplementation in maintaining optimal gain. During phase B, hens consuming the RCP diet gained on average 42% more weight than those fed the LCP diet. Additionally, an ME x EZ interaction during phase A indicated a significant increase in BW gain when feeding the RME diet with EZ supplementation compared with no EZ. This interaction could have been the result of an increase of 4 kcal/hen per d achieved when supplementing the RME diet with EZ [28, 29].

A CP x EZ interaction (P ≤ 0.04) was noted overall. From 18 to 60 wk, feeding an RCP diet with EZ resulted in higher BW gain (P ≤ 0.05) than with any of the other CP and EZ dietary treatment combinations. No differences in BW gain were observed as a result of feeding LCP with or without EZ. In phase C, however, an ME x CP x EZ interaction (P ≤ 0.04) occurred, in which feeding the RME/LCP diet without EZ resulted in higher BW gain (P ≤ 0.055) as compared with feeding the same diet with EZ. However, feeding hens an RME/RCP diet supplemented with EZ resulted in the greatest BW gain (P ≤ 0.004), as compared with feeding the RME/LCP diet with EZ (44.8 vs. –33.7 g/hen).

Similar to a previous report [30], neither ME nor EZ supplementation influenced egg production (Table 3Go). This was in contrast to a significant increase (1.2 or 6%) in egg production or eggs per hen housed when supplementing an LME diet with Avizyme 1500 [1]. A significant CP x EZ interaction was observed during phases B (P ≤ 0.03), C (P ≤ 0.02), and overall (P ≤ 0.04), which had a response pattern similar to that for feed intake. Although similar in pattern, indicating a direct effect of feed intake on egg production, the only significant difference when evaluating individual comparisons was with EZ supplementation when varying dietary CP (LCP < RCP).


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  		Table 3. Effect of dietary energy or protein, with or without enzyme, on egg production and egg weight from 18 to 60 wk of age
 
There was no effect of dietary ME on egg weight, whereas the LCP diet lowered egg weight (P ≤ 0.001) during all production phases (Table 3Go). Overall, case weight was 2.3% (47.1 vs. 46.0 lb/case) lower when feeding the LCP diets. During this time, the hen was growing and developing reproductively, producing essentially an egg a day. The reduction in egg weight throughout the trial may have been due to limited amino acid(s). Typically, there is a reduction in egg weight when feeding low-protein diets [27, 31–35]. It was noted previously [27] that a CP reduction of 2% points was adequate for maintaining several production traits, including egg weight. Enzyme supplementation also resulted in lower egg weights during phase B and overall (P ≤ 0.02 and 0.04). This effect was unexpected in view of the positive influence of exogenous enzymes on digestion and the release of nutrients that are subsequently available for maintenance and egg production. Others [30, 36] have noted similar responses when supplementing a corn and soybean meal diet with exogenous enzymes as an over-the-top application.

Egg mass (Table 4Go) was not affected by dietary ME; however, feeding LCP lowered the egg mass during phases B (P ≤ 0.0002) and C (P ≤ 0.0003) as well as overall (P ≤ 0.0004). Furthermore, egg mass was lower (P ≤ 0.05) with EZ supplementation during phase B (56.26 vs. 54.54 g), which was in contrast to an increase in egg mass when supplementing a corn- and soybean meal-based diet with Avizyme 1500 [1] and when supplementing a corn-, soybean meal-, and wheat middlings-based diet with Avizyme 1300 [3]. In addition, EZ supplementation had no effect on egg mass in wheat-based diets [37–39].


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  		Table 4. Effect of dietary energy or protein, with or without enzyme, on egg mass, FCR, and egg specific gravity from 18 to 60 wk of age
 
The response in feed conversion to dietary treatments was similar to that for egg mass, with only minor exceptions. Feed conversion ratio was not affected by changes in dietary ME, whereas feeding an LCP had an adverse effect on feed conversion in phases B and C, as well as overall. Feed conversion ratio was impaired by as much as 3.6% overall (1.91 vs. 1.98), with the largest response occurring during phase C (4.8% increase). This is in contrast to reports of improved FCR when feeding diets lowered in CP [27, 32]. Enzyme supplementation had a negative affect (P ≤ 0.05) on FCR in phase B and overall. This could be related to the ME x CP x EZ interaction (P ≤ 0.05) during phase B. Supplementing an RME/LCP diet with EZ impaired (P ≤ 0.003) FCR. In addition, with EZ supplementation, combining RME with LCP impaired (P ≤ 0.05) FCR as compared with combining RME with RCP. The impairment was associated with a minimal increase in feed intake but a reduction (P ≤ 0.03) in egg mass when feeding the RME/LCP diet with EZ supplementation (egg mass = ME x CP x EZ interaction = P ≤ 0.26). Impaired FCR values were noted when feeding hens an LME diet combined with RCP and EZ, compared with no EZ.

Shell Quality, Egg Composition, and Yolk Color
Shell quality was affected minimally by dietary treatments. Specific gravity (Table 4Go) was not affected by treatments, whereas percentage of wet shell (Table 5Go) was increased (P ≤ 0.01) during phase A and overall when feeding reduced-CP diets. This was probably related to the decrease in egg weight when feeding the LCP diets and not a result of an increase in shell deposition. In a previous report [30], feeding hens a diet with lower CP (4% points) reduced specific gravity. This could be related to the foundation of the shell (protein matrix) [40], because it was suggested that limiting amino acids for the development of this protein matrix may negatively influence shell quality.


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  		Table 5. Effect of dietary energy or protein, with or without enzyme, on wet albumen, yolk, and shell percentage1 from 18 to 60 wk of age
 
Egg albumen and yolk percentage (Table 5Go) were affected by dietary CP. Wet albumen percentage decreased (P ≤ 0.004), whereas yolk percentage increased (P ≤ 0.004) during each phase and overall at the higher CP levels, suggesting that the amino acids required for albumen synthesis (production requirements) may have been limited at the lower CP level. Previously, we observed reductions in albumen percentage when feeding diets lower in CP [27]. Penz and Jensen [32] also observed a similar reduction in albumen percentage when reducing dietary CP from 16 to 13%. In addition, it was reported that the hen would increase mRNA to compensate when feeding a reduced-CP diet [41], but possibly because of the lack of amino acids for synthesizing protein, albumen protein was not produced at the same level as in hens fed a higher protein diet. Failure to supply an adequate level of plasma amino acids to the magnum during egg albumen synthesis may also account for the reduction in egg size associated with feeding lower CP diets. The increase in yolk percentage was probably associated with the reduction in albumen percentage and egg size. Egg yolk is produced in the liver and continuously accumulated in the ovum until ovulation, and may not be affected by reducing dietary CP [27, 32, 42].

Yolk lightness (l) was not affected by dietary treatments (Table 6Go). Lowering ME and CP decreased red-greenness (a) during each phase and overall. In addition, an increase (P ≤ 0.0001) in yolk yellowness (b) was observed when feeding hens an LCP diet during the entire trial. When further evaluating yolk yellowness, an ME x CP interaction (P ≤ 0.05) was noted during phase C, which indicated that feeding hens an RME/LCP diet increased b (P ≤ 0.0001) as compared with yolks from hens fed an RME/RCP diet. In addition, hens fed an RME + LCP diet produced eggs with more yolk yellowness (P ≤ 0.009) than those fed the LME/LCP diet.


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  		Table 6. Effect of dietary energy or protein, with or without enzyme, on yolk color measurements from 18 to 60 wk of age
 
Increases in a and b would suggest that the yolk color was moving toward a deeper orange color. This is probably the result of increased corn (phase A: 55.05 vs. 61.86%) used in formulating the LCP diets, which would in turn increase the xanthophyll concentration and hence change the yolk color.

Energy Retention (Percent and Absolute) and Digestibility
Lowering CP increased (P ≤ 0.0001) the percentage of energy retained at 38 wk of age (Table 7Go). However, when feeding the LCP or LME diet, the absolute energy retained significantly decreased at 50, 60, and 38 to 60 wk of age. These results were probably due to the decrease in feed intake when feeding LCP diets with EZ and the minimal change when feeding hens diets lower in ME. There was no effect of EZ supplementation on percentage or absolute energy retention.


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  		Table 7. Effect of dietary energy or protein, with or without enzyme, on percentage and absolute energy retention and digestibility from 18 to 60 wk of age
 
At 38 wk of age, an ME x EZ interaction (P ≤ 0.003) resulted from an increased percentage of energy retention (P ≤ 0.05) in hens fed an LME diet with EZ, as compared with no EZ supplementation. Without EZ, hens fed an RME diet retained a significantly greater percentage of energy than those consuming the LME diet. However, when EZ was supplemented, energy had no effect on the percentage of energy retained.

Three-way interactions were observed at 50 (P ≤ 0.03) and 60 (P ≤ 0.02) wk of age (Table 7Go). At 50 wk, when hens were fed an RME diet, adjustments in neither dietary CP nor EZ supplementation affected the percentage of energy retained. When feeding an LME/RCP diet, EZ supplementation had minimal effects on the energy retained. However, when feeding an LME/LCP diet, EZ supplementation significantly increased the percentage of energy retained. In addition, when feeding an LME diet without EZ, CP had little effect on the percentage of energy retained, but when hens were fed a diet supplemented with EZ, combining LME with LCP significantly increased the percentage of energy retained. Responses observed at 60 wk of age were similar, with 2 exceptions. When hens were fed an RME diet, lowering the CP significantly reduced the percentage of energy retained, whereas effects were minimal when diets were supplemented with EZ. In addition, when hens were fed an LME diet without EZ, lowering the CP significantly reduced the percentage of energy retained.

Only an ME x EZ interaction (P ≤ 0.03) was observed in regard to energy digestibility, and this occurred at 60 wk (Table 7Go). A significant increase in energy digestibility occurred by lowering ME without supplementing EZ. In addition, supplementing LME diets with EZ increased (P ≤ 0.0004) the hens’ ability to digest energy and was similar to that of hens consuming an RME diet with EZ.

Protein Retention (Percent and Absolute) and Digestibility
Similar to observations noted with energy retention (Table 7Go), lowering the dietary CP increased (P ≤ 0.0007) the percentage of protein retained at 38 wk of age (Table 8Go). Although the percentage of protein retained increased, absolute protein retained decreased on average by 10.1 and 14.4% during phase A and overall, respectively. These observations may be the result of lower feed intake and possibly the hens’ inability to utilize available protein, as noted by a decrease in digestibility at 60 wk.


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  		Table 8. Effect of dietary energy or protein, with or without enzyme, on percentage and absolute protein retention and digestibility from 18 to 60 wk of age
 
At 38 wk, there was an ME x EZ interaction (P ≤ 0.05). Feeding the RME diet supplemented with EZ decreased (P ≤ 0.006) the percentage of protein retention (Table 8Go). In addition, hens fed the LME diet with EZ retained a higher (P ≤ 0.02) percentage of protein than those fed an RME diet supplemented with EZ. All other comparisons were similar. This interaction was also noted for overall absolute protein retained. When an RME diet was supplemented with EZ, absolute protein retention was significantly lowered. In addition, with no EZ, lowering ME reduced the daily protein retained.

As with the percentage of energy retention, there were ME x CP x EZ interactions at 50 (P ≤ 0.006) and 60 (P ≤ 0.0009) wk for percentage of protein retention (Table 8Go). The interaction at 50 wk was similar to that observed for percentage of energy retention, with one exception. Adding EZ to an LME/RCP diet significantly reduced the percentage of protein retention. However, at 60 wk, the percentage of protein retention was not affected by feeding an LCP diet without EZ or supplementing an RCP/RME diet with EZ. When hens were fed a diet with LCP and LME, the percentage of protein retained increased significantly with EZ supplementation. In addition, these hens also retained more (P < 0.05) protein than hens fed an RCP/LME diet with EZ.

Significant ME x CP x EZ interactions at 38 (P ≤ 0.04), 50 (P ≤ 0.01), and 60 (P ≤ 0.04) wk were observed for absolute protein retention (Table 8Go). At 38 wk, there were no significant differences when feeding the RME diets and varying CP or supplementing EZ. However, combining LME diets with RCP and EZ resulted in higher (P ≤ 0.006) absolute protein retention. When supplementing an LME diet with EZ, feeding the optimal level of CP was important, as noted by a significant reduction in absolute protein retained when lowering CP. At 50 wk, there were no significant differences when feeding the RME diets with EZ, but feeding the LCP diets significantly reduced absolute protein retained. Moreover, when feeding an LME diet, lowering CP significantly reduced absolute protein retention without EZ. However, supplementing the LME/RCP diet with EZ significantly reduced absolute protein retained daily. Last, at 60 wk absolute protein retained when feeding an RME diet was lowered with LCP, with further reductions when EZ was added to the RME/LCP diet. In addition, when feeding an LME/LCP diet, EZ supplementation increased (P ≤ 0.01) absolute protein retention. Additionally, without EZ, lowering CP in an LME diet caused hens to retain significantly less protein per day.

At 60 wk, protein digestibility was significantly affected by ME and CP main effects, which are not discussed because of the presence of significant 2-way interactions. For the ME x CP interaction (P ≤ 0.03), the greatest protein digestibility was found when hens were fed an RME/RCP diet as compared with feeding an RME/LCP or LME/RCP diet. The ME x EZ interaction (P ≤ 0.02) was similar to that for energy digestibility at 60 wk (Table 7Go).

Nitrogen Excretion
Overall, excreta contained on average 5% nitrogen (Table 9Go), which is similar to that reported previously [27]. Although varying ME had no effect, supplementing EZ increased (P ≤ 0.05) excreta nitrogen at 50 wk.


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  		Table 9. Effect of dietary energy or protein, with or without enzyme, on excreta nitrogen and economic evaluation from 18 to 60 wk of age
 
Metabolizable energy x CP interactions were observed at 38 (P ≤ 0.01) and 60 (P ≤ 0.05) wk. At 38 wk, excreta nitrogen was decreased by lowering CP in an RME or LME diet. Additionally, feeding an LME/LCP diet reduced excreta nitrogen further than feeding an RME/LCP diet. This response was similar, as noted above for the percentage of protein retained, indicating that when hens were supplied an LME/LCP diet, protein retention was increased. At 60 wk, ME had no effect on excreta nitrogen when combined with LCP; however, lowering ME in an RCP diet resulted in less nitrogen excreted.

Overall, feeding LCP diets decreased (P ≤ 0.0001) excreta nitrogen by 17.3%, a trend that was noted at 38, 50, and 60 wk but that is not discussed here because of the ME x CP interaction noted above. Overall, the reduction in excreta nitrogen was lower than previously reported [7, 43] and may have been due to a more severe reduction in dietary CP.

Economics
Lowering ME (P ≤ 0.03) or CP (P ≤ 0.02) reduced the cost to produce a pound of egg (Table 9Go). Supplementation with EZ significantly increased the cost of producing a pound of egg during phase C as well as overall as a result of the aforementioned changes in egg mass (Table 4Go). The 3-way interaction noted during phase A suggests that although adding EZ to an LME or LCP diet increases the cost to produce a pound of egg, it was similar when added to an LME/LCP diet. Lowering CP alone or ME and CP significantly reduced feed cost as compared with a commercial diet (RME/RCP without EZ). The most economical feeding program from 18 to 38 wk of age was achieved by feeding hens an LCP diet, which was similar to feeding an LME diet or an LME/LCP diet. In addition to the reduction in input cost when feeding an LCP diet, a reduction in excreta nitrogen was achieved with similar performance. A similar response was noted during phase B, with 3 exceptions. Feeding the RME/LCP without EZ or the LME/LCP with EZ was similar to feeding the commercial diet, whereas feeding the RME/LCP with EZ was less cost effective. Although the overall ME x CP x EZ interaction was not significant (P ≤ 0.08), feeding hens the LME/LCP diet without EZ was the most economical as compared with feeding the commercial diet (P ≤ 0.024).


   CONCLUSIONS AND APPLICATIONS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
REFERENCES AND NOTES
 

  1. Hens responded to diets with lowered ME by increasing feed intake, thus eating to meet their energy requirement for maintenance and egg production.
  2. Lowering CP significantly reduced egg weight and impaired FCR.
  3. Supplementation with EZ did not improve performance when feeding hens an LCP diet and reduced intake, which in turn may have contributed to the lack of response.
  4. Supplementing a corn and soybean meal diet with EZ had little effect on performance, nutrient retention, or digestibility.
  5. Overall, excreta nitrogen was lowered significantly when feeding hens LCP diets, and lowering ME and CP may further decrease excreta nitrogen, but responses may be age dependent.
  6. From 18 to 60 wk of age, feed cost to produce a pound of egg mass was decreased when feeding an LME/LCP diet without EZ; however, lowering ME or CP reduced feed cost, whereas it was increased with EZ.


   FOOTNOTES
 
2 Current address: Commercial Poultry Nutrition, Land O’Lakes Purina Feed, LLC, 12200 N Ambassador Dr., Suite 225, Kansas City, MO 64163. Back


   REFERENCES AND NOTES
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 

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