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Effects of Dietary Fiber and Reduced Crude Protein on Nitrogen Balance and Egg Production in Laying Hens¹

S. A. Roberts^*, H. Xin, B. J. Kerr, J. R. Russell^* and K. Bregendahl^*,2

^* Department of Animal Science, and Department of Agricultural and Biosystems Engineering, Iowa State University, Ames 50011; and Swine Odor and Manure Management Research Unit, Agriculture Research Service, USDA, Ames, IA 50011

² Corresponding author: kristjan{at}iastate.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Ammonia emission is a major concern for the poultry industry and can be lowered by dietary inclusion of fibrous ingredients and by lowering the dietary CP content. The objectives of this research were to determine the effects of dietary fiber and reduced-CP diets, which may lower NH₃ emission, on egg production and N balance in laying hens. A total of 256 Hy-Line W-36 hens were fed diets with 2 contents of CP (normal and reduced) and 4 fiber treatments in a 2 x 4 factorial arrangement from 23 to 58 wk of age. The fiber treatments included a corn and soybean meal-based control diet and diets formulated with either 10.0% corn dried distillers grains with solubles (DDGS), 7.3% wheat middlings (WM), or 4.8% soybean hulls (SH) added to contribute equal amounts of neutral detergent fiber. The CP contents of the reduced-CP diets were approximately 1 percentage unit lower than that of the normal-CP diets. All diets were formulated on a digestible amino acid basis to be isoenergetic. There were no effects (P > 0.05) of including corn DDGS, WM, or SH in the diet on egg production, egg weight, egg mass, yolk color, feed consumption, feed utilization, or BW gain. Although the corn DDGS and WM diets resulted in an increase (P < 0.001) in N consumption, N excretion was not affected (P > 0.10) compared with hens fed the control diet. The reduced-CP diets did not affect egg weight, feed consumption, or BW gain (P > 0.05); however, egg production, egg mass, feed utilization, N consumption, and N excretion were lower than that from the hens fed the normal-CP diets (P < 0.05). The results of this study show that the diets containing 10% corn DDGS, 7% WM, or 5% SH did not affect egg production or N excretion. However, the 1% lower CP diets caused a lower egg production and lower N excretion.

Key Words: corn-dried distillers grains with solubles • egg production • reduced crude protein diet • soybean hull • wheat middlings

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Excretion of N, part of which is volatilized as NH₃ and lost to the atmosphere, is a concern to the poultry industry. In the United States, poultry (including laying hens) is the largest contributor of atmospheric NH₃ emissions among domestic animal species, accounting for 27% of the total NH₃ emissions in 2002 based on national emission inventory estimation (EPA, 2004; Aneja et al., 2006). Not only can NH₃ adversely affect health and production of poultry by contributing to deciliation of the trachea, corneal ulcers, impairment of macrophage function, reduced lung function, lower egg production, and lower BW gains (Kling and Quarles, 1974; Nagaraja et al., 1983; Carlile, 1984; Deaton et al., 1984; Omland, 2002; Miles et al., 2004), but it may also cause eutrophication of surface water resources and nuisance odors (De Boer et al., 2000; Angus et al., 2003; Ritz et al., 2004). The Federal Comprehensive Environmental Response, Compensation, and Liability Act and Emergency Planning and Community Right to Know Act require reporting of releases of NH₃ above 45 kg per day per animal-housing site, and the United Egg Producers animal husbandry guidelines (United Egg Producers, 2006) recommend atmospheric NH₃ concentrations below 25 ppm in laying-hen houses. Inclusion of feed ingredients with high concentrations of fiber has been shown to lower NH₃ emission from pigs and laying hens (Kreuzer and Machmuller, 1993; Tetens et al., 1996; Canh et al., 1997; Shriver et al., 2003; Roberts et al., 2007), and reduced-CP diets have been shown to decrease N excretion and NH₃ emission from pigs, broilers, and laying hens (Summers, 1993; Summers and Leeson, 1994; Bregendahl et al., 2002; Keshavarz and Austic, 2004). High-fiber or reduced-CP diets have been fed to laying hens without causing a depression in egg production (Summers, 1993; Leeson and Caston, 1996; Jaroni et al., 1999a; Lumpkins et al., 2005). However, the inclusion of high-fiber feed ingredients in diets fed to pigs or poultry may lower nutrient digestibility and, therefore, increase total N excretion (Jaroni et al., 1999b; Dilger et al., 2004; Hogberg and Lindberg, 2004). We hypothesized that including high-fiber feed ingredients and reducing the CP contents of laying-hen diets would contribute to a decrease in NH₃ emission from manure with no adverse effects on egg production or N balance. In a separate report, we showed that dietary inclusion of 10% corn dried distillers grains with solubles (DDGS), 7.3% wheat middlings (WM), or 4.8% soybean hulls (SH) lowered (P < 0.05) the NH₃ emission from laying-hen manure by up to 50% as a result of lowering the manure pH, but reducing the CP content by 1 percentage unit did not elicit a significant change in NH₃ emission (Roberts et al., 2007). The objectives of this study were to determine the effects of dietary fiber and reduced-CP diets on egg production, feed consumption, N and DM digestibilities, and N balance in laying hens.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Birds and Housing
A total of 256 Hy-Line W-36 laying hens were obtained from a commercial facility at 17 wk of age and placed in a completely enclosed fan-ventilated light- (12L:12D) and temperature- (20°C) controlled room. Hens were housed 2 per cage, corresponding to 619 cm² (96 in²) per hen, in wire-bottomed cages (Chore-Time, Milford, IN) each equipped with a plastic self-feeder and a nipple drinker. Feeders were fitted with a wire grate to minimize waste of feed but not restrict feed consumption. Photoperiod was increased incrementally according to the Hy-Line W-36 2003–2005 Commercial Management Guide (Hy-Line International, Des Moines, IA) to 16L:8D at 25 wk of age. Prelay and prepeak diets were formulated according to recommendations in the W-36 commercial management guide for 17 to 18 and 19 to 22 wk of age, respectively, and fed to all hens before the commencement of the trial. At 23 wk of age (corresponding to 95% production), hens were reassigned to cages according to a randomized complete block design with BW and cage location within the barn as blocking criteria, and hens were fed the treatment diets. The Iowa State University Institutional Animal Care and Use Committee approved techniques and procedures involved in the animal care and handling.

Experimental Diets
Before formulation of diets, all protein-supplying ingredients were analyzed for contents of total amino acids by methods 982.30E a, b, and c (AOAC, 2006) and for CP by method 990.03 (AOAC, 2006), ether extract by method 920.39A (AOAC, 2006), and crude fiber by method 978.10 (AOAC, 2006) at the Missouri Experiment Station Chemical Laboratories (University of Missouri, Columbia; Table 1). Ingredients were also analyzed for neutral detergent fiber by the method of Van Soest and Robertson (1979) using an Ankom fiber analyzer (Ankom Technology Corporation, Fairport, NY). The analyzed total amino acid contents were adjusted to true digestible amino acid contents using coefficients published by Ajinomoto Heartland (2005). The requirements for true digestible amino acids of the hens were estimated as 89% (i.e., the average true digestibility coefficient of the amino acids in corn and soybean meal) of the recommendations for total amino acids, which were derived from NRC (1994) and recent literature (Harms and Russell, 1996, 2000a,Harms and Russell, b; Russell and Harms, 1999; Faria et al., 2002; Antar et al., 2004). Target values for daily consumption of true digestible amino acids were as follows: 580 mg of Ile, 765 mg of Lys, 340 mg of Met, 640 mg of TSAA, 445 mg of Thr, 135 mg of Trp, and 625 mg of Val for hens 32 to 44 wk of age. Hens were phase-fed to account for changes in nutrient requirements and feed consumption with age: phase 1 (23 to 31 wk of age), phase 2 (32 to 44 wk of age), and phase 3 (45 to 58 wk of age) were formulated with 105, 100, and 95 of the amino acid target values, respectively. Diets were formulated for total Ca, nonphytate P, and ME contents according to recommendations in the W-36 commercial management guide; NaHCO₃ (American Soda, Parachute, CO) was included to equalize the calculated dietary electrolyte balance among diets within a phase. All diets contained Celite (Celite Corporation, Lompoc, CA) as a source of acid insoluble ash (AIA), used as an indigestible marker.

Hen BW was measured at the beginning of the experiment and after each phase. Feed consumption was recorded weekly and calculated as grams of feed disappearance over 7 d divided by the number of hen days, adjusted for mortalities (only 4 hens died during the study, of causes not attributed to the dietary treatments). Feed utilization was calculated weekly as grams of egg mass divided by kilograms of feed consumed.

N Balance.
Nitrogen balance was determined during wk 6 of phase 3 (birds at 51 wk of age). Manure was collected from each cage within 2 min of excretion over 4 h, placed into capped 50-mL centrifuge tubes, and stored on ice. Manure was analyzed for N contents using micro-Kjeldahl method 984.13 (AOAC, 2006) on a Kjeltech 1028 distilling unit (US Tecator Inc., Herndon, VA) on the day of collection, and the remaining sample was stored at –20°C until further analysis. Manure was thawed, dried, and analyzed for contents of AIA using the method of Vogtmann et al. (1975). Details of the manure collection and analyses are described by Roberts et al. (2007). Eggs from a 48-h collection period, during the same week as manure collection, were used for determination of egg N. Eggs were weighed, broken, and the albumen and yolk pooled within cage. The yolk-albumen mixture was weighed, 4 mL was removed for DM determination by drying at 70°C for 24 h, and the remainder frozen at –20°C. The frozen egg contents were lyophilized and subsequently analyzed for N content.

The following calculations were used to determine manure excretion, N excretion, N retention, apparent fecal N digestibility, and apparent fecal DM digestibility. The excretion of DM manure was calculated as follows: Manure_Excretion = (AIA_Feed x Feed_Consumption)/AIA_Manure, where Manure_Excretion = the manure excreted (g); AIA_Feed and AIA_Manure = the analyzed AIA contents of feed and manure, respectively (%); and Feed_Consumption = the feed consumed (g). Nitrogen excretion was calculated as follows: N_Excretion = Manure_Excretion x N_Manure, where N_Excretion = the N excreted (g) and N_Manure = the N content of the manure (%). The N retention was calculated as follows: N_Retention = N_Consumption – N_Egg – N_Excretion, where N_Retention = the N retained by the hen (g); N_Consumption = the N consumed (g); and N_Egg = the N in eggs (g). Apparent fecal N digestibility was calculated as follows: N_{Digestibility} = 100 – [100 x (N_Excretion/N_Consumption)], where N_{Digestibility} = the apparent fecal N digestibility of the N contents in the diet (%). The apparent fecal DM digestibility was calculated as follows: DM_{Digestibility} = 100 – [100 x (Manure_Excretion/Feed_Consumption)], where DM_{Digestibility} = the apparent fecal digestibility of the DM contents of the diet (%). All calculations were made on a DM basis, and results are expressed on a per-hen, per-day basis.

Statistical Analyses
Statistical analyses were performed using JMP (version 5.1.2, SAS Institute Inc., Cary, NC). Data were analyzed by ANOVA appropriate for a randomized complete block design with 16 blocks and 8 dietary treatments in a 2 x 4 factorial arrangement (Morris, 1999). The ANOVA model included effects of block, protein, fiber, and the interaction of protein and fiber. Dunnett’s multiple comparison procedure (Dunnett, 1955) was used to compare the results from each of the fiber treatments to the results from the control; the main effect of protein was used to compare the reduced- and normal-CP diets. The experimental unit was a cage with 2 hens, and P 0.05 was considered significant. There were no interactions (P > 0.05) between dietary fiber and CP contents, so the main effects of each factor are discussed separately.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION REFERENCES

 
Adjusting diet composition may decrease the amount of NH₃ that is lost from laying-hen facilities but may also potentially affect egg production and N balance. Although the high-fiber ingredients resulted in a decrease in the total NH₃ emission and emission rate (Roberts et al., 2007), feeding high-fiber ingredients is only an acceptable method for egg producers to mitigate NH₃ emission if there are no adverse effects on egg production. In the present study, there were no effects (P > 0.05) of dietary inclusion of 10% corn DDGS, 7% WM, or 5% SH on egg production, egg weight, egg mass, feed consumption, feed utilization, or BW gain compared with the control diet (Table 6). Diets were formulated to be isoenergetic, with equal contents of true digestible Lys and TSAA; hence, no differences were expected.

Nitrogen consumption was higher for hens fed corn DDGS or WM compared with hens fed the control diet (Table 8; P < 0.001). The higher N consumption was expected, because amino acids in fibrous feed ingredients are typically less digestible than those in low-fiber ingredients (Kirchgessner et al., 1994; Stein et al., 2006), requiring consumption of larger amounts of total amino acids (and, therefore, N) to satisfy the requirement for digestible amino acids. The higher N consumption of the hens fed the corn DDGS or WM diet was expected to result in a higher N excretion than that of the control-fed hens. However, N excretion was unaffected by the corn DDGS or WM treatment (P > 0.10). As a result, N retention was higher for the hens fed WM (P = 0.01) but not corn DDGS (P = 0.08) compared with hens fed the control diet. Although N retention was unexpectedly negative for the control-fed hens, N retentions of the hens fed the corn DDGS, WM, or SH diets were not different from 0 (P > 0.05; t-test), indicating that hens fed the high-fiber diets were neither gaining nor losing body N.

There were no effects of the reduced-CP diet on egg weight, feed consumption, or BW gain during the trial (Table 6; P > 0.10). Contrary to expectations, however, egg production, egg mass, and feed utilization were lower from the hens consuming the reduced-CP diets compared with hens fed the normal-CP diets during phases 2 and 3 (P < 0.05). Because amino acid-supplemented reduced-CP diets have been fed to laying hens with no discernible effect on egg production parameters (Summers, 1993; Summers and Leeson, 1994; Keshavarz and Austic, 2004), the poorer production observed for the hens fed the reduced-CP diets in the present experiment suggests that the target amino acid values for 1 or more amino acids were set too low for the phase 2 and 3 diets. Indeed, Meluzzi et al. (2001) found that reduced-CP, amino acid-supplemented diets sustained performance for 8 wk, after which time egg production and egg mass were lower from hens fed 13.6 and 15.3% CP diets compared with hens fed 17.1% CP diets.

Nitrogen consumption was lower (P < 0.01) for hens fed the reduced-CP diets than that of hens fed the normal-CP diets (Table 8). This difference was expected, because the reduced-CP diets contained less N than the normal-CP diets, and hens fed the normal- or reduced-CP diets consumed similar amounts of feed (P > 0.10). Hens fed the reduced-CP diets had similar N content in eggs and N retention compared with that of the control-fed hens (P > 0.10). The decreased N consumption of the hens fed the reduced-CP diets, therefore, resulted in decreased N excretion compared with hens fed the normal-CP diets (P < 0.05). The lower N excretion is in agreement with results from studies in which broilers, pigs, or laying hens were fed reduced-CP diets (Kreuzer and Machmuller, 1993; Summers, 1993; Summers and Leeson, 1994; Tetens et al., 1996; Canh et al., 1997; Bregendahl et al., 2002; Shriver et al., 2003; Keshavarz and Austic, 2004). Although others have shown that lower N excretion from reduced-CP-fed animals resulted in lower NH₃ excretion (Latimier and Dourmad, 1993; Liang et al., 2005), the lower N excretion from the hens in the present study did not result in lower NH₃ emission (Roberts et al., 2007).

Results of this study showed that inclusion of 10% corn DDGS, 7% WM, or 5% SH in laying-hen diets had no adverse effects on egg production, egg quality, or N balance. Therefore, increasing the dietary fiber content may be a feasible option to mitigate NH₃ emission in a commercial egg-production operation (Roberts et al., 2007). The reduced-CP diets resulted in decreased egg production, which may be attributed to an amino acid deficiency.

	ACKNOWLEDGMENTS

 
We would like to thank the Midwest Poultry Consortium, St. Paul, Minnesota, and Novus International Inc., St. Louis, Missouri, for financial support. Additionally, we would like to acknowledge Feed Energy Company, Des Moines, Iowa, and Archer Daniels Midland Company, Des Moines, Iowa, for in-kind contributions and Novus International Inc. for amino acid analyses. The assistance provided by personnel in the Xin, Kerr, and Bregendahl laboratories and at the Iowa State University Poultry Science Research Center, as well as statistical guidance from Philip Dixon in the Department of Statistics at Iowa State University, is greatly appreciated.

	FOOTNOTES

 
¹ Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by Iowa State University or the USDA and does not imply approval to the exclusion of other products that may be suitable.

Received for publication December 28, 2006. Accepted for publication April 24, 2007.

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