The effect of dietary crude protein on growth, ammonia concentration, and litter composition in broilers

EDUCATION AND PRODUCTION The Effect of Dietary Crude Protein on Growth, Ammonia Concentration, and Litter Composition in Broilers1 N. S. FERGUSON,* R. S. GATES,†,2 J. L. TARABA,† A. H. CANTOR,‡ A. J. PESCATORE,‡ M. J. FORD,‡ and D. J. BURNHAM§ *Animal Science and Poultry Science Department, University of Natal, P Bag X01, Scottsville, 3209, South Africa, Departments of †Biosystems and Agricultural Engineering and ‡Animal Sciences, University of Kentucky, Lexington, Kentucky 40546, and §Heartland Lysine Inc., 8430 W Bryn Mawr Ave, Chicago, Illinois 60631 from 215 g/kg (11.5 g/kg lysine) to 196 g/kg (11.3 g/kg lysine), but feed intake and feed:gain ratio increased. However, reducing CP did cause equilibrium NH3 gas concentration and litter N to decline by 31 and 16.5%, respectively. Both of these advantages will improve air quality within the housing facility and possibly reduce heating costs during winter associated with higher ventilation rates required to reduce elevated NH3 gas concentrations.

(Key words: crude protein, ammonia, litter composition, broiler) 1998 Poultry Science 77:1481–1487

INTRODUCTION There have been a number of attempts to reduce the amount of N wasted and particularly the amount of NH3 produced in broiler chickens (Carlile, 1984). As NH3 is produced by the microbial breakdown of uric acid in the broiler litter it is possible, in theory, to lower the rate and equilibrium NH3 gas concentration by manipulating either the source or the process of NH3 production. Some of the methods used to control NH3 have included dietary manipulation (Jacob et al., 1994; Ferguson et al., 1998), adequate ventilation and careful litter management (Reece et al., 1979; O’Connor et al., 1988; Hartung and Phillips, 1994), and the addition of chemicals to the litter such as yucca saponin (Johnston et al., 1981), antibiotics (Kitai and Arakawa, 1979), formaldehyde (Veloso et al., 1974), zeolites (Nakaue et al., 1981), and phosphates (Carlile, 1984). Although the use of chemicals to neutralize NH3 or reduce microbial fermentation has recently gained some commercial acceptance, it is realized at an additional cost. Correctly applied ventilation programs have been shown to be effective for reducing NH3 concentrations in poultry

Received for publication August 12, 1997. Accepted for publication June 24, 1998. 1Paper Number 97-05-106 of the Kentucky Agricultural Experiment Station. 2To whom correspondence should be addressed: gates@bae. uky.edu

houses but at an energy cost, particularly during winter months when additional heating is required (Gates et al., 1996; Hartung and Phillips, 1994; Xin et al., 1996). The most efficient and possibly the cheapest method of controlling NH3 production is to reduce the amount of N excreted from the birds. This reduction in excretion can be achieved by reducing the amount of dietary CP fed to the birds and supplementing with synthetic amino acids or by reducing the CP of the feed as the birds increase in weight by increasing the number of feeds provided during the growing-finishing phase. According to Jacobs et al. (1994) the former method reduced N excretion by 28% and the latter by up to 21% with a 2.5% reduction in dietary CP. Most N losses are due to the inadequacy of supplied protein to meet the amino acid requirements of the bird and particularly the imbalances between the different essential amino acids and between the essential and nonessential amino acids that are supplied in the diet. The closer the available essential amino acids in the diet match or balance the growth and maintenance requirements of the bird, the less amino acid degradation and excretion will occur. Amino acid and energy requirements of broilers vary widely with newer genotypes, and it is unclear whether these requirements are truly known (Gous, 1998). Current practice is to supply protein somewhat in excess of accepted requirements. This practice occurs because of the need to formulate rations to satisfy practical least cost rather than, say, maximum protein accretion levels.

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ABSTRACT An experiment was conducted to determine the effect of diets with reduced CP and supplemental amino acids on broiler performance, N excretion, litter characteristics, and equilibrium NH3 gas concentration. Results suggest that reducing CP (and lysine) below 241 g/kg (13.7 g/kg lysine) in the diets fed during the first 3 wk may slightly increase feed:gain and therefore may not be advisable. During the period 22 to 43 d of age there were no significant differences in weight gain and BW at 6 wk of age when reducing CP

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FERGUSON ET AL. TABLE 1. Composition and nutrient content of the experimental diets Starter period: 1 to 21 d Low

Medium1

High

Corn Soybean meal 48% Corn oil Ground limestone Dicalcium phosphate Salt L-lysine HCl DL-methionine L-threonine L-tryptophan Vitamin-mineral premix2 Analyzed composition ME, Mcal/kg3 Crude protein (N × 6.25) Total lysine Total Met and Cys Total threonine Total tryptophan Total isoleucine

617.0 308.0 31.0 12.0 19.5 4.8 2.0 2.7 0.5 0.2 2.5

545.0 373.0 40.5 12.0 19.0 4.8 1.0 2.3 0.3 0.1 2.5

475.0 438.0 50.0 12.0 18.5 4.8 ... 2.0 ... ... 2.5

3.10 219.0 12.0 9.4 8.5 3.1 9.1

3.10 241.3 13.7 9.5 9.7 3.4 10.1

3.10 264.0 15.4 9.6 10.8 3.7 11.0

Low (g/kg) 724.0 214.0 25.3 11.1 16.9 4.0 1.1 2.0 0.1 0.1 2.0 3.18 165.3 9.3 7.3 7.0 1.9 6.4

Medium1

High

655.0 275.0 35.0 11.0 16.0 4.0 1.0 2.0 ... ... 2.0

586.0 336.0 44.8 10.9 15.9 3.7 ... 1.0 ... ... 2.0

3.18 195.8 11.3 7.5 8.4 2.3 8.1

3.18 214.7 11.5 7.7 8.7 2.5 8.4

1Medium

diet is a 1:1 blend of High and Low diets. the following per kilogram of diet: vitamin A, 6,000 IU; cholecalciferol, 1,000 IU; vitamin E, 15 IU; meadione dimethylpyrimidinol bisulfate, 2.0 mg; thiamin, 2.7 mg; riboflavin, 5.4 mg; niacin, 27 mg; pantothenic acid, 11 mg; pyridoxine, 2.5 mg; biotin, 0.23 mg; folacin, 0.6 mg; vitamin B12, 0.014 mg; ethoxyquin, 125 mg; copper, 6 mg; iodine, 0.53 mg; iron, 120 mg; manganese, 83 mg; zinc, 60 mg; cobalt, 5 mg. 3Formulated value. 2Provided

In a previous experiment (Ferguson et al., 1998) we found that if essential amino acid requirements are met, dietary CP can be decreased by nearly two percentage points before production is adversely affected. However, only two CP treatments were used and the CP contents of the diets fed during the first 3 wk of age were too low. There were also significant interactions between protein and phosphorus treatments that made bird response to solely a reduction in dietary CP unclear. No significant effects for either CP or phosphorus were found for equilibrium NH3 gas concentration, with substantial variation among replicates, suggesting that additional samples per replicate were needed. The objective of this study was to determine the effect of diets with lowered CP and supplemented amino acids on broiler performance, N excretion, litter characteristics, and equilibrium NH3 gas concentration.

MATERIALS AND METHODS

Birds and Management Seven hundred and ninety male commercial broilers3 were randomly assigned to 15 floor pens. Each pen (2.4 m × 1.8 m) was equipped with one infrared lamp brooder, an automatic bell drinker, and two tube feeders (only one was used during the first 3 wk of age). Each of the concrete

3Cobb

× Avian.

floor pens was covered with approximately 8 cm of good quality pine wood shavings. Five pens of 48 chicks each were randomly assigned to one of three dietary treatments. Birds that died were replaced by birds that had been fed the same dietary treatment in an attempt to maintain consistent stocking densities (0.09 m2 per bird) throughout the 6 wk. To avoid the effect that air flow has on litter composition, pens with similar air velocity at bird head height were assigned to each treatment. The average air velocity did not exceed 0.2 m/s at bird head height. Weekly BW and feed consumption were determined. Birds that died during each week were weighed and the feed intakes and feed conversion were adjusted according to the number of bird days. The experiment was completed after 43 d.

Diets and Treatments Experimental treatments consisted of three diets: 1) high CP (High), 2) low CP with additional synthetic amino acids (Low), and 3) an equal blend (1:1) of High and Low CP treatments (Medium). Crude protein and amino acid contents of corn and soybean used to formulate the diets were obtained from their respective amino acid analyses. Within a time period all diets were isocaloric. The starter and grower diets were fed during Weeks 1 through 3 and Weeks 4 through 6, respectively. The composition and nutrient values for the diets are shown in Table 1. The Low protein treatment was supplemented with more essential amino acids to meet NRC minimum recommended values (NRC, 1994). However, the analyzed data showed that the

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Ingredient

Grower period: 22 to 43 d

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DIETARY PROTEIN AND LITTER EQUILIBRIUM AMMONIA TABLE 2. Effect of dietary crude protein on 1 to 21 d, 22 to 43 d, and 1 to 43 d average feed intake, weight gain, and feed conversion Feed Intake

Weight gain

Protein treatments

Days 1 to 21

Days 22 to 431

Days 1 to 431

Low Medium High SEM (n = 5) Significance:

1,072 1,056 1,043 16.9 NS

4,238a 4,203a 3,972b 55.3 *

5,304a 5,259a 5,015b 70.0 *

Feed:gain

Days 1 to 21

Days 22 to 43

Days 1 to 43

Days 1 to 21

Days 22 to 431

Days 1 to 431

767 778 791 13.6 NS

1,814b 1,900a 1,902a 25.3 *

2,581b 2,679a 2,693a 32.8 *

1.40a 1.36b 1.32b 0.012 ***

(g:g) 2.34a 2.21b 2.09c 0.031 ***

2.06a 1.96b 1.86c 0.023 ***

(g)

a-cMeans

within a column with no common superscript differ significantly (P < 0.05). Low protein replication was excluded from the feed intake and feed:gain treatment means because of very high feed wastage (n = 4). *P < 0.05. ***P < 0.001. 1One

Gas and Litter Sampling To examine the effects of diet manipulation on the litter equilibrium NH3 gas concentration, a 19-L container was pressed into the litter between the two feeders and the drinker. The litter was prepared by first removing the top 5 to 10 mm, which typically consisted of a hard, dry, crusted layer, and exposing wet litter. The removal of the top layer was to ensure a more uniform estimate of equilibrium NH3 gas concentration. The gas sampling container contained a small fan to mix the sample air at a constant velocity (1 m/s) to ensure that the surface-air boundary layer was sufficiently disturbed. Every 2 min for a period of approximately 20 min, the sampling line was purged and a 2-mL sample of air was diverted from within the container to a Bruel and Kjaer 1302 photoacoustic infrared gas monitor6 to measure NH3 concentration. The sampled air was then returned to the isolation container. Equilibrium NH3 gas concentration was determined as the steady-state concentration. Gas sampling was repeated every week in each pen and required 1 full d. Further details can be found in Ferguson et al. (1998) and Gates et al. (1997). A litter sample was taken weekly from each pen from the same area from which the NH3 concentration was measured. The samples were obtained by removing the first 10 mm of the exposed surface after the top layer had been removed. The litter samples were collected in freezer bags and refrigerated until the next day when pH

4Ameribond brand, Lignotech Inc., Rothschild, WI 5Beckman Systems Inc., Fullerton, CA 92634-3100. 6California Analytical Inc., Orange, CA 92665.

54474.

measurements were taken and moisture contents were determined by weighing samples before and after placing in an oven at 103 C for 24 h. The remaining sample was freeze-dried for 7 d and then milled using a 1-mm sieve. The milled samples were then analyzed for N using the procedures described by the AOAC (1995). Significance levels of P < 0.10 were used for separation of treatment means for the equilibrium NH3 gas concentration measurements, because when analyzing real time measurements there are a number of dynamic factors affecting litter. These factors include pH, moisture content and litter N content. Variation in these factors can result in large variations among replicates (Ferguson et al., 1998).

Statistical Analysis Data were subjected to analysis of variance using the one-way ANOVA procedure of SigmaStat (1995). To determine the relationship between NH3 and litter quality, the Forward Stepwise Regression procedure was used. The independent variables considered were N intake, pH, moisture, and N content of the litter. For all measurements, the pen means represented the experimental unit. Significant differences were determined by Tukey’s test and the Student’s t tests.

RESULTS AND DISCUSSION Bird responses over 1 to 21, 22 to 43, and 1 to 43 d in feed intake, weight gain, and feed conversion to decreasing CP are shown in Table 2. Over the first 3 wk, there were no significant differences between treatments in feed intake and weight gain but the feed:gain ratio increased with a reduction in CP. However, there were no significant differences in feed conversion between the Medium and High treatments but rather between High and Low, and Medium and Low treatments. Although there were no significant differences in feed intake between treatments from 1 and 21 d of age, the response does show a trend for intake to increase as CP of the diet decreases. This result can be explained by comparing the levels of amino acids in the three starter-period diets. Although the Low protein treatment was formu-

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lysine level was lower than the recommended value (9.3 vs 10.0 g/kg). A pellet binder4 was added to the diets at a rate of 16.7 g/kg and the diets were pelleted at a local commercial feed mill. Each feed was sampled and analyzed for Kjeldahl N, dry matter (AOAC, 1995) and, after acid hydrolysis, amino acid composition using a high performance cation exchange resin column.5 Each feed sample was analyzed twice.

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7Means

are reported followed by the standard error of means.

In an experiment to determine the role of an essential: nonessential amino acid ratio in broiler chicks, Bedford and Summers (1985) found that as long as the essential amino acids comprised 55% of CP, then the level of dietary CP was not a factor affecting growth and feed intake. However, when the ratios were lower (35:65 and 45:55 essential:nonessential, respectively), then dietary CP was a significant factor, with increased performance associated with higher protein contents. Han et al. (1992) observed that amino N in itself can be a limiting factor in low protein diets. In this experiment, all the diets contained essential:nonessential amino acid ratios of close to 55:45, suggesting that the reduced performance of birds on the Low protein treatment was not due to insufficient amounts of essential amino acids relative to the nonessential protein content. According to Gous and Morris (1985) and Abebe and Morris (1990), the concentration of the first limiting amino acid had the most important effect on growth and feed intake. Gous and Morris (1985) found that increasing CP of a diet deficient in an essential amino acid, by the addition of nonessential amino acids, did not elicit a significant response. In this study, the lysine content of the Low treatment fed in the last 3 wk was 18 and 19% lower than Medium and High treatments, respectively, and 7% lower than the NRC value of 10.0 g/kg (Table 1). Therefore, it may be argued that the growth response observed in the current data was not a CP effect but rather a lysine-limiting effect. However, it is also possible that there were differences in the amino acid digestibility of the diets because they had various levels of corn, soybean meal, and synthetic amino acids, with crystalline amino acids being more available than protein-bound amino acids (Chung and Baker, 1992). Thus, even if each diet had similar total amino acid levels, the actual amount of amino acid available to the bird may have been significantly different, with the consequence that one or more amino acids may have become limiting at the nutrient uptake level. Even though the Low treatment diet contained lysine in a more readily available form, it is still likely to be limiting compared to the Medium and High treatments. This limitation would explain the measured improvement in growth and feed:gain associated with increasing the level of total lysine from the Low (9.3 g/kg) to Medium (11.3 g/kg) to High (11.5 g/kg) treatments. The results of reducing CP levels in the diet on average bird weight at 21 and 43 d of age are shown in Table 3. Unlike in a previous experiment (Ferguson et al., 1998), in which there were significant differences at 21 d of age, there were no significant differences in the BW at 21 d of age, although there was a trend for lower BW at lower protein levels. By 43 d of age there was a significant difference in BW between the High (2,728 ± 32.7 g) and Medium (2,713 ± 27.8 g) treatments, on the one hand, and the Low treatment (2,616 ± 10.3 g) on the other. These results confirm the idea that there is a critical dietary CP level below which bird performance will decline. In this

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lated to contain amino acid levels higher than the requirements of the bird, the concentrations were at least 20% lower than the High treatment (except methionine and cystine). The data appear to follow the linear phase of a typical amino acid response curve, which would suggest that the increased feed intake was a result of either a limiting amino acid or too low nonessential:essential amino acid ratio (Gous and Morris, 1985; Morris et al., 1987). In a previous experiment Ferguson et al. (1998) observed similar trends, confirming that a reduction in CP during the starter period (1 to 21 d) may not adversely affect feed intake but could possibly reduce either weight gains or feed conversion. However, other authors have observed equal weight gain and feed efficiency when comparing high protein vs low protein diets supplemented with amino acids during the 7 to 21 d period (Schutte, 1987; Parr and Summers, 1991; Han et al., 1992). The response in feed intake in the last 3 wk and for the whole 6-wk period followed the same trend as in the first 3 wk except that there were significant differences between treatments and particularly between the High vs Medium (5.8% respective increase) and High vs Low (6.6% respective increase) treatments. The reduction in CP did not affect live weight gains from Day 1 to 21 but did result in significantly reduced gains (4.6% reduction) over the 22 to 43 d and 1 to 43 d period when comparing the Low treatment with either High or Medium treatments. There were no differences between the Medium and High treatments over the 22 to 43 d (1,900 ± 20.1 vs 1,902 ± 25.3 g, respectively)7 and 1 to 43 d period (2,679 ± 27.7 vs 2,693 ± 32.9 g, respectively). These results suggest that there is a point below which any further reduction in CP of the diet will cause a reduction in growth despite the addition of synthetic amino acids, unless an essential amino acid was limiting. In this experiment, a decline from 210 to 188 g/kg CP had no effect on weight gain but a further reduction from 188 to 165 g/kg significantly reduced weight gains by 86 g over the period 22 to 43 d and by 98 g for the whole 43 d. Despite the Medium and High CP treatments resulting in similar weight gains over the 22 to 43 d and 1 to 43 d periods, they had significantly different feed:gain ratios (2.213 ± 0. 037 vs 2.089 ± 0.026, respectively, and 1.964 ± 0.028 vs 1.862 ± 0.019, respectively). This result agrees with Cabel and Walroup’s (1991) conclusion that protein requirements for minimum feed conversion are greater than that for weight gain. The increased feed conversion with decreased CP is a result of the birds on the Medium treatment consuming close to 6% more feed per unit BW gain than birds on the High treatment. However on the Low protein treatment, birds not only ate more but also grew more slowly. It would therefore appear that a 2 percentage point reduction in dietary CP will result in a 5% increase in feed:gain, mainly as a result of increased feed intake.

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DIETARY PROTEIN AND LITTER EQUILIBRIUM AMMONIA TABLE 3. Effect of dietary crude protein on average bird weight at 21 and 43 d of age Body weight

Protein treatment

21 d

Low Medium High SEM (n = 5) Significance

802 812 826 10.3 NS

43 d (g) 2,616b 2,713a 2,728a 25.5 *

a,bMeans in a column with no common superscript differ significantly (P < 0.05). *P < 0.05.

TABLE 4. The effect of dietary crude protein on the mean ± SEM of equilibrium ammonia gas concentration and litter characteristics1 Treatment Low Medium High Significance a,bMeans

NH3 (ppm) 53 ± 7.2 58 ± 5.1 83 ± 13.8 †

pH

Moisture

5.0 ± 0.20b 5.1 ± 0.09a,b 5.5 ± 0.34a *

560 ± 10.8b 569 ± 16.2b 603 ± 29.1a *

Nitrogen2 (g/kg) 47 ± 2.0b 49 ± 1.4b 59 ± 0.2a ***

in a column with no common superscript differ significantly (P < 0.05). pen from the Medium and High treatments (n = 4) were excluded because of unusually high air flow over the litter, which affected the equilibrium NH3 gas concentration and litter characteristics (Low treatment n = 5). 2Nitrogen values expressed on a dry matter basis. †P < 0.10. *P < 0.05. ***P < 0.001. 1One

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experiment, the results suggest that reducing the CP content below 18.8% in the diet fed from 3 to 6 wk of age will adversely affect feed intake, feed conversion, weight gain, and BW at 6 wk of age. Results of the litter quality and equilibrium NH3 gas concentration are shown in Table 4. Equilibrium NH3 gas concentration was significantly affected (P < 0.10) by CP, with a trend for NH3 concentration to decrease with decreasing dietary CP. There was a 31% (25 ppm) decline in equilibrium NH3 gas concentration associated with a reduction in dietary CP and supplementation with amino acids. There were significant differences (P < 0.05) between treatments in the pH, moisture content, and litter N (Table 4). The increase in acidity of the litter observed in the Low treatment (pH = 5.0) may be associated with a drier litter and may also contribute to the reduction of NH3 production by inhibiting those bacteria that hydrolyze uric acid and urea to produce NH3 and therefore reduce the amount available for release (Taraba et al., 1980). The lower pH reduces the unionized NH3 available for volatilization. The very low pH values observed in this experiment of between 5.0 and 5.5 compared to the normal range of 7.5 to 8.5 (Anthony et al., 1994; Ferguson et al., 1998) is probably

due to our removal of the top 5 to 10 mm layer of compacted, crusty litter prior to taking NH3 measurements and litter samples. The material immediately beneath the top layer showed signs of decomposition and, hence, an increase in the acidity of the litter. Moisture content of the litter was correlated with CP levels, although the position of feeders and water troughs was exactly the same in each pen. The equilibrium NH3 gas concentration increased with increasing moisture content of the litter. It has been documented that NH3 emission is positively correlated with litter moisture content (Elliott and Collins, 1982; Carr et al., 1990), whereas previous work by these authors (Ferguson et al., 1998) indicated a negative correlation. Litter pH has been shown to be correlated with litter moisture content (Carr et al., 1990; Ferguson et al., 1998). Moisture content and pH of the litter regulate the release of NH3 (Elliott and Collins, 1982). The measured NH3 concentration in the gas phase is in equilibrium with free, or unionized, NH3 contained in the moisture of the litter. The free NH3 depends directly on total NH3 content of the litter and on the disassociation constant, which in turn depends on the [H+] concentration. Small changes in pH (–log[H+]) result in large percentage changes in [H+]. For example, the measured increase in mean pH between low and high CP treatments (5.0 vs 5.5) represents a threefold increase in [H+]. Thus, the larger SEM for pH in the high CP treatment translates to greater variation in measured equilibrium NH3 gas concentration. Reducing dietary CP from 215 to 196 or 165 g/kg did result in a significant reduction in the amount of N in the litter but there were no further significant decreases between feeding 196 and 165 g/kg. The potential then exists to not only reduce NH3 emissions by reducing CP and maintaining adequate amino acid levels, but also to reduce the amount of N in broiler litter. To determine which variables had a significant effect on the equilibrium NH3 gas concentration, a regression analysis was performed. Moisture content, N intake, and

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litter N content had the most effect on equilibrium concentrations of NH3, such that: NH3 = –392.3 (± 74.72) + 0.64(± 0.38) × NI + 0.78 (± 0.38) × MC – 14.52 (± 8.31) × Litter N; r2 = 0.81

ACKNOWLEDGMENTS The authors would like to acknowledge the technical and financial support of Heartland Lysine Inc. In addition, this work was partly funded by USDA Regional Project S-261, “Interior Environment and Energy Use in Poultry and Livestock Facilities.”

REFERENCES Abebe, S., and T. R. Morris, 1990. Note on the effects of protein concentration on responses to dietary lysine by chicks. Br. Poult. Sci. 31:225–260. Anthony, N. B., J. M. Balog, F. B. Staudinger, C. W. Wall, R. D. Walker, and W. E. Huff, 1994. Effect of a urease inhibitor and ceiling fans on ascites in broilers. 1. Environmental variability and incidence of ascites. Poultry Sci. 73: 801–809. AOAC, 1995. Official Methods of Analysis. 16th ed. Association of Official Analytical Chemists, Arlington, VA.

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where NH3 = equilibrium ammonia gas concentration (parts per million); NI = N intake between 3 and 6 wk of age (grams per bird); MC = moisture content of the litter (grams per kilogram); Litter N = N content of the litter (grams per kilogram DM); pH was not included. However, if [H+] concentration rather than pH were used, it would be included. The relationship between equilibrium NH3 gas concentration and moisture content of the litter was the same as has been previously reported (Carr et al., 1990; Groot KoerKamp and Elzing, 1996). The results of this experiment suggest that reducing CP concentration (and lysine) below 215 g/kg (13.7 g/ kg lysine) in the diets fed to chicks during the first 3 wk may slightly increase feed:gain and therefore may not be advisable. During the period 22 to 43 d there were no significant differences in weight gain and BW at 6 wk of age when reducing the CP from 215 g/kg (11.5 g/kg lysine) to 196 g/kg (11.3 g/kg lysine) but it was at the expense of increased feed intake and, hence, a reduced feed conversion. However there were advantages to reducing the CP, as equilibrium NH3 gas concentration declined by 31% and litter N was reduced by 16.5% on a dry matter basis. Both of these advantages can help improve air quality within the housing facility and possibly reduce the heating costs during winter associated with higher ventilation rates required to reduce elevated NH3 gas concentrations. Reduced litter N may also translate into decreased environmental loading for land application of poultry litter; reduced NH3 emissions from housing results in less atmospheric loading.

Bedford, M. R., and J. D. Summers, 1985. Influence of the ratio of essential to non-essential amino acids on performance and carcass composition of the broiler chick. Br. Poult. Sci. 26:483–491. Cabel, M. C., and P. W. Waldroup, 1991. Effect of dietary protein level and length of feeding on performance and abdominal fat content of broiler chickens. Poultry Sci. 70: 1550–1558. Carlile, I. 1984. Ammonia in poultry houses: A literature review. World’s Poult. Sci. J. 40:99–113. Carr, L. E., F. W. Wheaton, and L. W. Douglass, 1990. Empirical models to determine ammonia concentrations from broiler chicken litter. Trans. ASAE 33:1337–1342. Chung, T. K., and D. H. Baker, 1992. Apparent and true amino acid digestibility of a crystalline amino acid mixture and of casein: comparison of values obtained with ilealcannulated pigs and cecectomized cockerels. J. Anim. Sci. 70:3781–3790. Elliott, H. A., and N. E. Collins, 1982. Factors affecting ammonia release in broiler litter. Trans. ASAE 25(2): 413–418, 424. Ferguson, N. S., R. S. Gates, J. L. Taraba, A. H. Cantor, A. J. Pescatore, M. L. Straw, M. J.Ford, and D. J. Burnham, 1998. The effect of dietary protein and phosphorus on ammonia concentration and litter composition in broilers. Poultry Sci. 77:1085–1093. Gates, R. S., D. G. Overhults, and S. H. Zhang. 1996. Minimum ventilation for modern broiler facilities. Trans. ASAE 39(3): 1135–1144. Gates, R. S., J. L. Taraba, N. S. Ferguson, and L. W. Turner. 1997. A technique for determining ammonia equilibrium and volatilization from broiler litter. Presented at the 1997 ASAE Annual International Meeting, Paper No. 97-4074, ASAE, St. Joseph, MI. Gous, R. M., 1998. Making progress in the nutrition of broilers. Poultry Sci. 77:111–117. Gous, R. M., and T. R. Morris, 1985. Evaluation of a diet dilution technique for measuring the response of broiler chickens to increasing concentrations of lysine. Br. Poult. Sci. 26:147–161. Groot KoerKamp, P.W.G., and A. Elzing, 1996. Degradation of nitrogeneous somponents in and volatization of ammonia from litter in aviary housing systems for laying hens. Trans. ASAE 39(1):211–218. Han, Y., H. Suzuki, C. M. Parsons, and D. H. Baker, 1992. Amino acid fortification of a low-protein corn and soyabean meal diet for chicks. Poultry Sci. 71:1168–1178. Hartung, J., and V. R. Phillips, 1994. Control of gaseous emissions from livestock buildings and manure storages. J. Agric. Eng. Res. 57:173–189. Jacob, J. P., R. Blair, D. C. Bennett, T. A. Scott, and R. C. Newberry, 1994. The effect of dietary protein and amino acid levels during the grower phase on nitrogen excretion of broiler chickens. Page 309 in: Proceedings of Canadian Animal Science Meetings, University of Saskatchewan, Saskatoon, SK, Canada. Johnston, N. L., C. L. Quarles, D. J. Fagerberg, and D. D. Caveny, 1981. Evaluation of yucca saponin on performance and ammonia suppression. Poultry Sci. 60: 2289–2296. Kitai, K., and A. Arakawa, 1979. Effect of antibiotics and caprylohydrozamic acid on ammonia gas from chicken excreta. Br. Poult. Sci. 20:55–62.

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