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Poult Sci 2007. 86:684-690
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METABOLISM AND NUTRITION

Nutrient Digestibility and Mass Balance in Laying Hens Fed a Commercial or Acidifying Diet1

W. Wu-Haan*, W. J. Powers*,2, C. R. Angel{dagger}, C. E. Hale, III{ddagger} and T. J. Applegate§

* Department of Animal Science, Iowa State University, Ames 50011; {dagger} Animal and Avian Sciences, University of Maryland, College Park 20742; {ddagger} Rose Acre Farms, Seymour, IN 47274; and § Department of Animal Sciences, Purdue University, West Lafayette, IN 47907

2 Corresponding author: wpowers{at}msu.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
The objectives of the current study were to evaluate the effect of an acidifying diet (gypsum) combined with zeolite and slightly reduced crude protein (R) vs. a control diet (C) on nutrient retention in laying hens and compare 3 approaches to estimating nutrient excretion from hens: 1) mass balance calculation (feed nutrients – egg nutrient), 2) use of an indigestible marker with analyzed feed and excreta nutrient content, and 3) an environmental chamber that allowed for capturing all excreted and volatilized nutrients. Hens (n = 640) were allocated randomly to 8 environmental chambers for 3-wk periods. Excreta samples were collected at the end of each trial to estimate apparent retention of N, S, P, and Ca. No diet effects on apparent retention of N were observed (53.44%, P > 0.05). Apparent retention of S, P, and Ca decreased in hens fed R diet (18.7, – 11.4, and 22.6%, respectively) compared with hens fed the C diet (40.7, 0.3, and 28.6%, respectively; P < 0.05). Total N excretion from hens fed the C and R diet was not different (1.16 g/hen/d); however, mass of chamber N remaining in excreta following the 3-wk period was less from hens fed the C diet (1.27 kg) than from hens fed the R diet (1.43 kg). Gaseous emissions of NH3 over the 3-wk period from hens fed the C diet (0.74 kg per chamber) were greater than emissions from hens fed the R diet (0.45 kg). The 3-wk S excretion mass (estimated using the calculation, indigestible marker, and environmental chamber methods, respectively) was greater from hens fed the R diet (1.85, 1.54, and 1.27 kg, respectively) compared with hens fed the C diet (0.24, 0.20, and 0.14 kg, respectively). The 3-wk P excretion was similar between diets (0.68 kg). Results demonstrate that feeding the acidified diet resulted in decreased N emissions, but because of the acidulant fed, greatly increased S excretion and emissions.

Key Words: laying hen • nitrogen • sulfur • mass balance • retention


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Diet acidifiers have been used as a strategy to reduce N volatilization from excreta (McCrory and Hobbs, 2001; Kim et al., 2004). Gypsum is an acidogenic compound that has been used as a Ca source in laying hen diets without reducing laying hen performance (Keshavarz, 1991). A variety of additives adsorb NH3, NH4+, or both; the most commonly used are zeolites, which exhibit a strong preference for binding nitrogenous cations such as NH+4, resulting in lower NH3 concentration in excreta (Nakaue and Koelliker, 1981). Wu-Haan et al. (2007) reported that a reduced emissions diet containing gypsum, zeolites, and slightly reduced protein reduced emissions of NH3, methane, and carbon dioxide and increased emissions of H2S without affecting hen performance. How-ever, it is not clear what effect this diet will have on nutrient retention and nutrient excretion.

The objectives of the current study were to evaluate the effect of an acidifying diet combined with zeolite and reduced crude protein on nutrient retention in laying hens and to compare 3 approaches for estimating nutrient excretion from hens: 1) mass balance calculation (feed nutrients – egg nutrient), 2) use of an indigestible marker with analyzed diet and excreta nutrient content, and 3) an environmental chamber that allowed for capturing all excreted and volatilized nutrients.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Experimental Design

Animal-related experimental procedures were approved by the Iowa State University Committee for the Care and Use of Animals. The study consisted of 3 trials, each lasting 3 weeks, utilizing Hyline W36 hens, starting at 21 (trial 1), 38 (trial 2), and 59 wk (trial 3) of age. All hens were obtained from high-rise laying hen houses (Rose Acres Farms, Stuart, IA), located 1 h away from the research location. During each trial, a total of 640 hens (initial BW = 1.36, 1.47, and 1.52 kg in trial 1, 2, and 3; respectively) were allocated randomly to 1 of 8 chambers (indirect calorimeters) and fed for a 3-wk period (ending age was 24, 41, and 62 wk for trial 1, 2, and 3, respectively). In each chamber, 80 birds were divided among four 2-cage units (10 birds per cage, 355 cm2 of cage space per bird). Temperature in all chambers was maintained at 22 ± 2 ° C. Relative humidity ranged from 20 to 80%. Light (10 to 20 lx) was provided from 0600 to 1800 h for 21-wk-old birds and 0600 to 2200 h for the 38- and 59-wk-old birds. The light program was managed to mimic that of the commercial farm and meet the recommendations of the Hy-Line W36 Commercial Guide (Hy-line W36 Commercial Management Guide 2003–2005, Hy-Line International).

Diets

A reduced emission (R) or a control (C) diet was assigned randomly to each of the 8 chambers (4 chambers per diet) with the chamber constituting the experimental unit. The R diet was formulated at a reduced crude protein content and a 6.9% combination of CaSO4 and zeolites, which replaced 35% of the limestone on a calcium content basis (Wu-Haan et al., 2007). On an analyzed basis, the R diet contained about 5 times more S than did the C diet as a result of additional gypsum. The R and C diets contained similar Ca, P, and energy. Both diets were formulated to meet or exceed NRC (1994) nutrient requirements and are described by Wu-Haan et al. (2007).

Apparent Retention of Nitrogen, Sulfur, Calcium, and Phosphorus

Animal performance measures are reported by Wu-Haan et al. (2007). Celite (World Minerals Inc., Santa Barbara, CA) was added to the diets at an inclusion level of 1% for 38 and 59 wk of age hens to serve as an indigestible marker. Feed samples were collected weekly and pooled to produce a single composite sample of each diet for each of the 3 trials. Twenty-four hour excreta collection samples were used for apparent retention determinations. The excreta samples were freeze-dried (– 80 ° C), ground, and packaged in plastic bags, and stored (22 ° C) for analyses. Diet and excreta N, P, S, and Ca content were analyzed. Nitrogen was determined using the Kjeldahl method (AOAC, 1984). Diet and excreta total P were measured using the colorimetric molybdovanadate procedure (AOAC, 1984) and a Hach DR/4000 spectrophotometer (Hach Company, Loveland, CO). Sulfur content was determined using a Vario Max CNS machine (Elementar Corp., Mt. Laurel, NJ). Calcium was analyzed by the Central Analytical Laboratory at the University of Arkansas (Fayetteville) using an inductively coupled plasma technique. Acid-insoluble ash (AIA) was determined using the procedures described by Vogtmann et al. (1975).

Apparent retention was calculated as described by (Scott et al., 1976):


Formula

Nutrient Mass Balance Determination

All excreta produced during each 3-wk period accumulated in the chamber, and the mass of excreta was measured at the end of each trial. A subsample of the excreta was collected for N, P, and S analyses using the methods described previously.

All N, S, and P inputs and outputs of the system were calculated. Nutrient inputs were constituted by the feed. Nutrient outputs included nutrients exported in eggs, excreta, and gaseous emissions to the atmosphere. Content of N, S, and P in a 60.8-g-of-weight egg (with shell) was estimated at 1 g, 87.6 mg, and 126.1 mg, respectively (Cotterill et al., 1977; Stadelman and Pratt, 1989). Laying hens utilized in the current study were mature, and BW change was minimal; hence it was ignored. Mortality was 0.7% and ignored in the equation.

Three methods were compared for estimating nutrient excretions. The first method was a mass balance approach taking into account nutrient inputs and nutrients harvested as eggs. The calculated amount of excreta N (MN), S (MS), and P (MP) excreted during the 3 trials (3 ages) was calculated as


Formula 1(1)

The total weight of feed and eggs are represented as Wfeed and Weggs. Concentration of N, S, and P are represented as Cfeed and Ceggs for feed and eggs, respectively.

The second method (marker) estimated excretions of N (EN), S (ES), and P (EP) by hens during the 3-wk periods using an indigestible marker and analyzed feed and excreta nutrient content:


Formula 2(2)

The Wexcreta represents the estimated total weight of excreta based on measured feed intake as well as feed and excreta concentrations of the indigestible marker. The Wexcreta was calculated as follows: Wexcreta = (AIAfeed x Wfeed)/AIAexcreta, where AIAfeed and AIAexcreta represent the concentration of indigestible marker in feed and in the 24-h excreta sample, respectively, as measured in acid-insoluble ash. Concentration of N, S, and P of the 24-h excreta sample is represented by Cexcreta.

The third method (chamber) involved calculating the mass of N (TN), S (TS), and P (TP) excreted by hens during the 3-wk period by weighing the mass (Wexcreta) and sub-sampling for nutrient analyses (Cexcreta) and adding these to the mass of N and S emitted (EN,S) to the atmosphere during the 3-wk period, based on measured emissions of NH3, NO, NO2, NO2, and H2S:


Formula 3(3)

Detailed emissions data (NH3, NO, NO2, SO2, and H2S) are reported by Wu-Haan et al. (2007).

Statistical Analyses

Data were analyzed using a GLM procedure of SAS version 8.4 (SAS Institute, Cary, NC). The model included the fixed effects of diet (C and R diets), age, and the interaction between age and diet. Significant differences among the means were declared at P < 0.05.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Performance measures are reported by Wu-Haan et al. (2007). Across ages, the average daily egg weight (56.3 g), average daily egg production (81.0%), and average daily feed intake (92.4 g/hen/d) of hens fed the R diet were not different from hens fed the C diet.

Apparent Retention of Nitrogen, Sulfur, Calcium, and Phosphorus

Apparent retention, based on marker method of N is presented in Table 1Go. Across ages, apparent retention of N in hens fed the R diet (51.78%) was not different from hens fed the C diet (55.11%). Apparent retention of N in hens at 41 and 62 wk was 53.41 and 53.48%, respectively, with no age or diet x age interaction effects observed. These results are similar to work by Keshavarz and Austic (2004) who reported that apparent retention of N was 48.8% when hens were fed a diet containing 16.5% protein. The difference in retention values between Keshavarz and Austic (2004) and the current study are possibly due to ingredients utilized in the diets and the method used to determine retention (ileal vs. excreta sampling).


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  		Table 1. Apparent retention of excreta N, S, P, and Ca of hens fed a control (C) or reduced emission (R) diet at 41 and 62 wk of Hy-Line W36 age1
 
Apparent retention of S is presented in Table 1Go. Sulfur retention was affected by diet and hen age. Across ages, apparent retention of S decreased in hens fed the R diet (18.70%) compared with hens fed the C diet (40.71%). Hens at 41 wk (34.71%) had greater apparent retention of S than hens at 62 wk of age (24.71%). Gypsum, a sulfur-containing compound, was added to the diet as an acidifying agent, which led to greater S excretion and likely caused reduced digestive efficiency.

Across ages, apparent retention of P was lower in hens fed the R diet (– 11.41%) than hens fed the C diet (0.30%; Table 2Go). No age effect was observed. The negative retention is much lower than previously reported values (15 to 40%; Carlos and Edwards, 1998; Um and Paik, 1999) and is likely a reflection of the relatively high concentration of P in the diet (average 0.63%) combined with the unaccounted part of the P balance equation related to bone mineralization/demineralization.


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  		Table 2. Composition (as fed-basis) of the reduced emission diet (R) and the control diet (C) fed to 21-, 38- and 59-wk-old laying hens1
 
Apparent retention of Ca is also presented in Table 1Go. Across ages, apparent retention of Ca was reduced in hens fed the R diet (22.6%) compared with hens fed the C diet (28.6%). These results are similar to that reported by Jalal and Scheideler (2001) who demonstrated a Ca retention of 29.3%. The acidifying diet likely shifted the acid-base balance of hen’s blood system resulting in greater Ca excretion (Keshavarz, 1991) and reduced digestive efficiency in hens fed the R diet.

Nutrient Mass Balance

On an analyzed basis, across diet and age, the concentrations of N, S, and P of the 24-h excreta samples were 4.61, 1.74, and 1.98% (DM basis), respectively. Across diet and age the concentrations of excreta N, S, and P that were present in the excreta accumulated during the 3-wk period trial were 3.96, 2.02, and 1.99% (DM basis). The increased concentration of S but not of N or P in the 24-h sample compared with the cumulative sample is difficult to explain given that excreta did not dry considerably during storage and that N and S volatilized. Analytical error combined with sampling error is the most likely explanation. Sampling error would include feathers in the accumulated sample but not in the 24-h sample.

Chamber N mass balance is presented in Table 3Go. Nitrogen intake was greater in hens fed the C diet (4.20 kg) than in hens fed the R diet (3.98 kg) because of the higher dietary protein concentration of the C diet given that feed intake was similar (92.1 and 92.7 g/hen/d for hens fed the C and R diets, respectively) in both diets (Wu-Haan et al., 2007). The N content of eggs with shells has been previously estimated as 1.7% (Cotterill et al., 1977; Stadelman and Pratt, 1989), and these values were used to calculate the mass of N that left the system in the form of egg during the course of the trial. Total N content of eggs produced by hens over the course of the 21-d housing period was assumed to be similar for hens fed the C and R diets (1.27 kg), based on no differences in egg production (Wu-Haan et al., 2007). Age did affect egg production (Wu-Haan et al., 2007); as a result of this the N exported in eggs was greater for hens at 41 wk (1.38 kg) of age than for hens at 24 (1.22 kg) and 62 wk (1.21 kg) of age. The N content of excreta accumulated during the 3-wk trial period for hens fed the C diet (1.27 kg) was less than for hens fed the R diet (1.43 kg). However, emissions of NH3 from hens fed the C diet (0.74 kg) were greater than emissions from hens fed the R diet (0.45 kg), likely the result of the R diet’s ability to trap N via acidification, resulting in less NH3 volatilization.


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  		Table 3. Chamber mass balance of nitrogen (N) during a 3-wk period of hens (80 hens per chamber) fed an acidifying diet supplemented with gypsum, zeolites, and slightly reduced crude protein diet (R) at 21, 38, and 59 wk of age compared to commercial diet (C)1
 
Nitrogen excretion data were estimated using 3 methods: mass balance calculation (feed - egg), an indigestible marker combined with concentration measures, and use of the environmental chamber to capture all emissions (equations [1], [2], and [3], respectively). Using equation [1], N excretion from hens fed the C and R diets were 2.93 and 2.70 kg, respectively, over the 3-wk trial period. Estimated N excretion using equation [2] was 1.88 and 1.92 kg from hens fed the C and R diets, respectively. Measured N excretion after the 3-wk accumulation period (equation [3]) resulted in an estimated 2.01 kg of N excretion from hens fed the C diet and 1.89 kg from hens fed the R diet. Using equation [2] (marker method) resulted in a N excretion value that was only 69.3% of the value that resulted from using the mass balance approach (equation [1]) but was similar to the value obtained using equation [3] (environmental chamber). Differences in values that resulted from application of the 3 different equations could be due to the N lost during sampling and storage (such as dust, feather) that was not considered in the mass balance calculation. The emissions of N2 and N2O were not measured because of equipment limitations; however, the contribution of these 2 gases is likely small. Dinitrogen gas emissions have been reported as significant contributors to N losses from anaerobic lagoons as a result of chemical, or nonbiological, denitrification (Harper et al., 2004). Harper et al. (2004) theorized that NH+ 4 oxidizes to N2 at very low O2 pressures. In their work, Harper et al. (2004) estimate that as much as 43% of N entering the farm was ultimately lost as N2. Nitrous oxide would form also as the result of anaerobic conditions and is highly unstable. Harper et al. (2004) measured N2O emissions from swine lagoons and estimated N2O emissions as representing 0.1% of N inputs into the farm system.

Chamber mass balance of S data is presented in Table 4Go. Sulfur intake was greater for hens fed the R diet (1.95 kg) than hens fed the C diet (0.35 kg) due to the addition of sulfur (CaSO4) to the R diet. The sulfur content of eggs has been previously estimated as 0.14% (Cotterill et al., 1977; Stadelman and Pratt, 1989), and this value was used in estimating the mass of S removed from the system in eggs over the course of the trial. The S content of excreta after 3 wk of storage was lower for hens fed the C diet (0.14 kg) than hens fed the R diet (1.26 kg). Emissions of H2S from hens fed the C diet (1.89 g) were also less than emissions from hens fed the R diet (6.70 g). Using equations [1], [2], and [3], S excretion over the 3-wk period was greater from hens fed the R diet (1.85, 1.54, and 1.27 kg, respectively) compared with hens fed the C diet (0.24, 0.20, and 0.14 kg, respectively). Using equation [2] (marker method) resulted in an S excretion value that was only 83% of the value that resulted from using the mass balance approach (equation 1) and 123% of the value obtained using equation [3] (environmental chamber). The mass balance approach may reflect outdated values of S for egg composition, thereby overestimating S retention, whereas the marker method did not account for the S content of feathers because feathers were excluded from the 24-h sample used in the marker method (equation [2]) but were present on the accumulated sample used with equation [3].


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  		Table 4. Chamber mass balance of S during a 3-wk period of hens (80 hens per chamber) fed an acidifying diet supplemented with gypsum, zeolites, and slightly reduced crude protein diet (R) at 21-, 38-, and 59-wk of age compared with the commercial diet (C)1
 
Chamber mass balance of P data are presented in Table 5Go. Phosphorus contents of feed consumed, eggs, and excreta were similar between hens fed the C diet (0.82, 0.11, and 0.66 kg, respectively) and hens fed the R diet (0.86, 0.11, and 0.69 kg, respectively). The average P excretions from hens fed both diets was equal to 0.40 g/hen/d. Age significantly affected P excretion. These results could be due to dietary P supplement differences at 21, 38, 59 wk of age relative to bird requirements. The P content of excreta at the end of the 3-wk excreta accumulation period was similar from hens fed the C (0.66 kg) and R diet (0.69 kg). Using equation [1], the calculated P excretions were the same (0.67 kg) from hens fed the R diet compared with hens fed the C diet. When the indigestible marker method was used (equation [2]), the estimated P excretions were greater from hens fed the R diet (0.92 kg) than those fed the C diet (0.72 kg). The measured P excretion using the chamber method was similar from hens fed the C (0.66 kg) and the R (0.69 kg). Using equation [2] (marker method) resulted in a P excretion value that was 122% of the value that resulted from using the mass balance approach (equation [1]) or the environmental chamber approach (equation [3]).


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  		Table 5. Chamber mass balance of P during a 3-wk period of hens (80 hens per chamber) fed an acidifying diet supplemented with gypsum, zeolites, and slightly reduced crude protein diet at 21, 38, and 59 wk of age compared with the commercial diet (C)1
 
Because P does not volatilize it was considered as a marker to evaluate the recovery from the environmental chambers. The findings demonstrate that the chamber method effectively accounted for nutrient excretions estimated using the mass balance method. Differences observed among the 3 methods of estimating nutrient excretion are likely attributed to losses of nutrients in feathers and feed dust, changes in BW and mortality, and sampling and equipment errors. For N and S, the estimated excretion method, based on 24-h collection of excreta when a marker was fed, was the closest to actual measured excretions using the chamber method.


   ACKNOWLEDGMENTS
 
This material is based upon work supported by the National Research Initiative Air Quality Program of the Cooperative State Research, Education, and Extension Service, USDA, under Agreement No. 2005-35112-15356 and funding received by the Iowa Egg Council. The authors wish to acknowledge Rose Acre Farms for donation of the hens and Sarah Zamzow and Martha Jeffrey for their laboratory assistance during the course of this project.


   FOOTNOTES
 
1 This material is based upon work supported by the National Research Initiative Air Quality Program of the Cooperative State Research, Education, and Extension Service, USDA, under agreement No. 2005-35112-15356 and funding received by the Iowa Egg Council. The authors would also like to thank Sarah Zamzow and Martha Jeffrey for their laboratory assistance during the course of this project. Back

Received for publication September 15, 2006. Accepted for publication December 9, 2006.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Association of Official Analytical Chemists. 1984. Official Methods of Analysis. 14th ed. Assoc. Off. Anal. Chem., Washington, DC.

Carlos, A. B., and H. M. Edwards Jr. 1998. The effects of 1,25-dihydroxycholecalciferol and phytase on the natural phytate phosphorus utilization by laying hens. Poult. Sci. 77:850–858.[Abstract/Free Full Text]

Cotterill, O. J., W. W. Marion, and E. C. Naber. 1977. A nutrient re-evaluation of shell eggs. Poult. Sci. 56:1927–1934.[Web of Science][Medline]

Harper, L. A., R. R. Sharpe, T. A. Parkin, A. DeVisscher, O. van Cleemout, and F. M. Byers. 2004. Nitrogen cycling through swine production systems: Ammonia, dinitrogen, and nitrous oxide emissions. J. Environ. Qual. 33:1189–1201.[Abstract/Free Full Text]

Jalal, M. A., and S. E. Scheideler. 2001. Effect of supplementation of two different sources of phytase on egg production parameters in laying hens and nutrient digestiblity. Poult. Sci. 80:1463–1471.[Abstract/Free Full Text]

Keshavarz, K. 1991. The effect of calcium sulfate (gypsum) in combination with different sources and forms of calcium carbonate on acid-base balance and eggshell quality. Poult. Sci. 70:1723–1731.

Keshavarz, K., and R. E. Austic. 2004. The use of low-protein, low-phosphorus, amino acid- and phytase-supplemented diets on laying hen performance and nitrogen and phosphorus excretion. Poult. Sci. 83:75–83.[Abstract/Free Full Text]

Kim, I. B., P. R. Ferket, W. J. Powers, H. H. Stein, and T. A. T. G. VanKempen. 2004. Effects of different dietary acidifier sources of calcium and phosphorus on ammonia, methane and odorant emission from growing-finishing pigs. Asian-australas. J. Anim. Sci. 17:1131–1138.

McCrory, D. F., and P. J. Hobbs. 2001. Additives to reduce ammonia and odor emissions from livestock wastes: A review. J. Environ. Qual. 30:345–355.[Abstract/Free Full Text]

Nakaue, H. S., and J. K. Koelliker. 1981. Studies with clinoptilolite in poultry. I. Effect of feeding varying levels of clinoptilolite (zeolite) to Dwarf Single Comb White Leghorn pullets and ammonia production. Poult. Sci. 60:944–949.

NRC. 1994. Nutrient Requirements of Poultry. 9th rev. ed. Natl. Res. Counc., Natl. Acad. Press, Washington, DC.

Scott, M. L., M. C. Nesheim, and R. J. Young. 1976. Pages 7–54 in Nutrition of the Chicken. M. L. Scott and Associates, Ithaca, NY.

Stadelman, W. J., and D. E. Pratt. 1989. Factors influencing composition of the hen’s egg. World Poult. Sci. 45:254–258.

Um, J. S., and K. Paik. 1999. Effects of microbial phytase supplementation on egg production, eggshell quality and mineral retention of laying hens fed different levels of phosphorus. Poult. Sci. 78:75–79.[Abstract/Free Full Text]

Vogtmann, H., P. Frirter, and A. L. Prabuck. 1975. A new method of determining metabolizability of energy and retention of fatty acids in broiler diets. Br. Poult. Sci. 16:531–534.[Web of Science][Medline]

Wu-Haan, W., W. J. Powers, C. R. Angel, C. E. Hale III, and T. J. Applegate. 2007. Effect of an acidifying diet combined with zeolite and slight protein reduction on air emissions from laying hens of different ages. Poult. Sci. 86:182–190.[Abstract/Free Full Text]





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