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Animal Feed Science and Technology146 (2008) 302–312

Available online at www.sciencedirect.com

Effect of varying dietary energy and protein onbroiler performance in hot climate

Q.U. Zaman a,1, T. Mushtaq a,∗,2, H. Nawaz a, M.A. Mirza a,S. Mahmood b, T. Ahmad c, M.E. Babar d, M.M.H. Mushtaq d

a Institute of Animal Nutrition and Feed Technology, University of Agriculture, Faisalabad 38040, Pakistanb Department of Poultry Science, University of Agriculture, Faisalabad 38040, Pakistan

c Faculty of Veterinary and Animal Sciences, University of Arid Agriculture, Rawalpindi 46300, Pakistand Faculty of Animal Production and Technology, University of Veterinary and

Animal Sciences, Lahore 54000, Pakistan

Received 22 June 2005; received in revised form 13 December 2007; accepted 30 January 2008

Abstract

The experiment was conducted to evaluate the effect of varying dietary metabolizable energy (ME)and crude protein (CP) concentrations on broiler performance during hot summer conditions. One dayold straight-run (0.50 male and 0.50 female) Starbro broiler chicks (n = 600) were randomly dividedinto 30 experimental units of 20 chicks each. Two levels of dietary ME (12.13 and 12.55 MJ/kg)and three levels of dietary CP (190, 210 and 230 g/kg) were used in a 2 × 3 factorial arrangementgiving six dietary treatments. Level of essential amino acids were maintained in all the diets bysupplementing low CP diets with crystalline amino acids. Each of the experimental diets was offeredto five replicates from hatching to 28 d of age. At the end of the experiment, two birds from eachreplicate were randomly selected for data on dressing yield, breast meat yield, abdominal fat, and liverand gizzard weights. Increasing dietary ME significantly increased the BW gain, abdominal fat andliver weights, and protein and fat contents of the carcass whereas the dry matter of carcass was reducedby increasing dietary ME. Dietary CP had quadratic effects on BW gain, F:G, carcass weight, and drymatter and protein contents of the meat. Breast weight and fat contents of meat increased linearly withincreasing CP of the diets. The low CP diets (i.e., 190 g/kg) at high ME (i.e., 12.55 MJ/kg) increased

∗ Corresponding author at: D-35, K.D.A. Scheme No. 1, Miran Muhammad Shah Road, Karachi, Pakistan.Tel.: +92 21 4543785; fax: +92 21 4543763.

E-mail address: tmmirza@fsd.paknet.com.pk (T. Mushtaq).1 Present address: Shahzor Feeds (Pvt.) Ltd., Lahore, Pakistan.2 Present address: Feed Tech. Division of Ghazi Brothers, Karachi 75350, Pakistan.

0377-8401/$ – see front matter © 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.anifeedsci.2008.01.006

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the BW gain, feed intake, carcass weight and improved F:G. However, lowest F:G was observed inbirds fed 210 g CP and 12.13 MJ ME/kg of diet. Protein and fat contents of the carcass were increasedin birds fed on diets having high CP and ME whereas dry matter contents of meat improved with highCP and low ME diets. The results of the trial showed a correlation between dietary CP and ME andhence the optimal value for one cannot be predicted without considering the other. Briefly, low CPwith high ME diets improved the overall performance when environmental temperature ranged from32 to 39 ◦C.© 2008 Elsevier B.V. All rights reserved.

Keywords: Dietary protein; Metabolizable energy; Amino acids; Broilers; Hot temperature

1. Introduction

High ambient temperature is very disruptive for broilers which results in reduced feedintake (Smith and Teeter, 1987) and weight gain as well as decreased carcass weights andabdominal fat (Pourrreza and Edriss, 1992) and increased mortality (Teeter and Belay, 1996;Reece et al., 1972). The time required to reach the desired market weight is also adverselyaffected (Hurby et al., 1995) during periods of heat stress.

Protein, having a major effect on growth performance, is the most expensive componentin broiler diets (Dirain and Waldroup, 2002). High dietary crude protein (CP) is generallydetrimental for broilers raised under high ambient temperatures due to higher heat incrementassociated with protein metabolism (Mushraf and Latshaw, 1999; Dirain and Waldroup,2002). Feeding high CP diets to heat-stressed broilers have shown adverse effects on weightgain, carcass composition, feed efficiency, and protein and energy utilization (Cheng et al.,1997).

Diets low in CP and supplemented with essential amino acids (AA) have shown improve-ments in growth rate and feed efficiency (Bregendahl et al., 2002; Rahman et al., 2002;Sterling et al., 2003; Si et al., 2004). Hurby et al. (1995) predicted that broilers reared at32 ◦C had lower protein requirements than those at 21 ◦C. Broiler chicks fed diets marginalin protein but fortified with methionine and lysine showed better performance than thosefed a diet higher in protein (Jennsen and Colnago, 1991).

The energy requirement of birds decreases as the ambient temperature increases above21 ◦C (Daghir, 1983). This reduced energy requirement is mainly due to reduction in energyrequirement for maintenance whereas the energy requirement for production is not influ-enced by environmental temperature (Hurwitz et al., 1980). High energy broiler starter dietsresulted in extra deposition of fat (Holsheimer and Jensen, 1991) indicating the wastage ofdietary energy.

Therefore, optimal broiler production in tropical environment requires an appropriatecombination of dietary ME and CP. This would not only ensure maximum utilization ofeach and every nutrient of the diet but also help to reduce the cost of production andenvironmental pollution associated with the loss of nitrogen in excreta. The present studywas, therefore, designed to investigate the effect of altering dietary ME and CP on theperformance and carcass characteristics of broilers reared at high ambient temperatures.

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2. Materials and methods

2.1. Birds and housing

The trial was conducted in a closed room with forced ventilation during June to Augustconsidered as the hot and humid months in Pakistan. Prior to the experiment, the broilerhouse was disinfected with whitewash and fumigated with formalin gas. Feeders anddrinkers were properly disinfected with 5% KMnO4 solution and dried under direct sun-light. The room was divided into 30 experimental units measuring 5 ft × 5 ft. A 5 cm-deepsoftwood shaving was used as bedding material over a concrete floor. During the first weekof experiment, the house temperature was maintained at 35 ◦C and after that daily cyclictemperature was followed. A 24 h light regime was provided throughout the experimentalperiod. Six-hundred-day-old straight-run Starbro broiler chicks (1/2 males and 1/2 females)were wing-banded, marked and randomly divided into 30 experimental units of 20 chickseach serving as a replicate. Each pen was equipped with separate manual drinker and feeder.Birds were vaccinated for Newcastle disease at 6 and 22 d and for infectious bursal diseaseat 11 and 22 d of age.

2.2. Experimental diets

Two levels of dietary ME (i.e., 12.13 and 12.55 MJ/kg) were used with three levels ofdietary CP (i.e., 190, 210 and 230 g/kg) in six experimental diets (Table 1) in such a way thatall the diets had very similar essential amino acid profile. Finished diets were analyzed fortheir CP, crude fibre, ether extract, and ash contents (AOAC, 1990). Each of the experimentaldiets was fed to five experimental units from hatching to 28 d of age. Feed and water wereprovided ad libitum during the experimental period.

2.3. Data collection

The experiment was terminated at the end of the 28th day and broiler performance wasmonitored in terms of body weight gain (BWG), feed intake (FI) and feed:gain (F:G). TheFI was also corrected for mortality, if any. On day 28, two birds from each replicate wererandomly selected and slaughtered to record the data on dressing yield, breast meat yield,abdominal fat and weight of visceral organs (heart, gizzard and liver). Proximate analysisof meat was done by the methods of AOAC (1990).

2.4. Statistical analyses

Pen mean was an experimental unit. The experimental design was completely ran-domised with factorial structure. Two levels of dietary ME (i.e., 12.13 and 12.55 MJ/kg)and three levels of dietary CP (i.e., 190, 210 and 230 g/kg) were analyzed as 2 × 3factorial design by General Linear Model using Minitab 13.1 (Minitab Inc., State Col-lage, PA). All the linear and quadratic terms were used in the statistical model foranalysis.

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Table 1Ingredient composition of experimental diets (g/kg)

Ingredients Metabolizable energy (MJ/kg) × crude protein (g/kg)

12.13 × 230 12.13 × 210 12.13 × 190 12.55 × 230 12.55 × 210 12.55 × 190

Corn 414.1 429.1 500.0 411.7 456.7 500.0Rice broken 50.0 70.0 71.2 30.0 50.0 50.1Rice polishings 65.0 65.0 65.0 65.0 65.0 65.0Corn gluten meal

(60% CP)40.0 24.4 7.0 40.0 30.0 7.0

Soybean meal 294.4 265.0 218.4 298.8 255.0 226.4Canola meal 40.0 59.5 48.8 40.0 40.0 44.5Fish meal 30.0 15.0 30.0 30.0 30.0 30.0Oil 18.7 20.0 9.20 36.6 29.5 26.7Molasses 20.0 20.0 20.0 20.0 20.0 20.0Dicalcium phosphate 11.2 14.3 12.1 11.2 11.8 11.9Limestone 10.8 11.4 10.7 10.9 10.8 10.7Premixa 5.0 5.0 5.0 5.0 5.0 5.0l-Lysine 0 0 0.90 0 0 0.80dl-Methionine 0.80 1.3 1.5 0.8 1.2 1.7l-Threonine 0 0 0.2 0 0 0.2

Nutrient composition (g/kg)Analyzed

Crude protein 229 209 190 229 208 188Crude fibre 34.1 38.4 35.9 38.2 36.7 35.5Ash 50.1 49.0 48.6 46.3 43.5 43.9

CalculatedME (MJ/kg) 12.13 12.13 12.13 12.55 12.55 12.55Calcium 10 10 10 10 10 10Available

phosphorus4.5 4.5 4.5 4.5 4.5 4.5

Arginine 14.3 13.3 12.0 14.4 12.9 12.0Glycine 10.4 9.4 8.9 10.1 9.5 8.9Serine 11.8 10.8 9.7 12.7 10.7 9.9Histidine 5.9 5.4 4.9 5.8 5.3 4.8Isoleucine 9.5 8.6 7.7 9.5 8.6 7.6Leucine 21.2 18.8 16.5 21.1 19.2 16.5Lysine 11 11 11 11 11 11Methionine 5.0 5.0 5.0 5.0 5.0 5.0Cystein 3.7 3.4 3.1 3.7 3.4 3.1Phenylalanine 11.3 10.1 8.8 11.3 10.1 8.8Tyrosine 9.8 8.8 7.8 9.8 9.8 8.0Threonine 8.4 8.0 8.0 8.5 8.0 8.0Tryptophan 3.1 2.8 2.4 3.1 2.7 2.5Valine 10.9 10.1 9.2 10.9 10.1 9.1

a Supplied per kg diet of finished feed: vitamin A (as retinyle acetate), 14,000 IU; vitamin D3 (as cholecalciferol),3500 IU; vitamin K (menadione sodium bisulfite), 2.8 mg; vitamin E (as d-�-tocopherol), 42 IU; biotin, 0.07 mg;folic acid, 1.7 mg; niacin, 35 mg; calcium pentothenate, 12.32 mg; pyridoxine, 3.36 mg; riboflavin, 7 mg; thiamin,1.7 mg; vitamin B12, 12.1 �g; Fe, 98 mg; Mn, 112 mg; Cu, 9.8 mg; Se, 0.07 mg; Zn, 70 mg; choline chloride,5.5 mg.

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3. Results

3.1. Live performance

Increasing the dietary ME improved the BWG. Dietary CP either as main effect or withdietary ME had a quadratic effect on BWG. The dietary CP had different effect on BWGwith respect to dietary ME where dietary CP for optimum body weight was 210 and 190 g/kgfor 12.13 and 12.55 MJ ME/kg, respectively. The low dietary ME levels had no effect onF:G whereas increasing CP significantly improved the F:G (quadratic response). Data onFI, BWG and FI are presented in Table 2. Dietary ME, CP or their interaction did not affectthe FI.

Table 2Effect of dietary energy and protein levels on body weight gain, feed consumption and feed:gain in broilers keptin heat stress environment

Weight gain (g) Feed intake (g) Feed:gain (g/g)

ME (MJ/kg)12.13 977 1736 1.7812.55 990 1753 1.77S.E.M.1 2.9 7.3 0.004

CP (g/kg)190 975 1761 1.81210 985 1732 1.76230 991 1740 1.76S.E.M.2 3.5 8.9 0.005

ME × CP12.13 × 190 949 1751 1.8512.13 × 210 999 1726 1.7312.13 × 230 982 1731 1.7612.55 × 190 1001 1771 1.7712.55 × 210 970 1738 1.7912.55 × 230 999 1750 1.75S.E.M.3 5.0 12.6 0.007

SignificanceME * – –

CP ** – ***

Linear *** – ***

Quadratic *** – ***

ME × CP *** – ***

ME × CP (linear) *** – ***

ME × CP (quadratic) *** – ***

1, 2, and 3Standard error of means of ME, CP and ME × CP, respectively.* P≤0.05.

** P≤0.01.*** P≤0.001.

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Table 3Effect of dietary energy and protein levels on carcass, breast, abdominal fat, liver, heart, and gizzard weights ofbroilers kept in heat stress environment

Carcassweight1

Breastweight1

Abdominalfat weight1

Liverweight1

Heart weight(g)

Gizzardweight (g)

ME (MJ/kg)12.13 62 16.0 2.3 3.7 11.6 26.812.55 63 16.2 2.4 3.8 12.2 27.7SEM2 0.2 0.06 0.03 0.03 0.25 0.33

CP (g/kg)190 62 15.9 2.3 3.7 11.8 27.2210 62 16.1 2.4 3.7 11.8 26.8230 623 16.3 2.4 3.7 12.0 27.7SEM3 0.2 0.08 0.04 0.04 0.30 0.41

ME × CP12.13 × 190 61 15.8 2.2 3.7 11.0 26.312.13 × 210 62 16.2 2.3 3.7 12.0 27.012.13 × 230 62 16.3 2.3 3.6 11.7 27.012.55 × 190 63 16.1 2.4 3.7 12.7 28.012.55 × 210 63 16.0 2.5 3.8 11.7 26.712.55 × 230 63 16.4 2.4 3.8 12.3 28.3SEM4 0.3 0.11 0.05 0.05 0.43 0.58

SignificanceME – – * * – –

CP * * – – – –Linear * * – – – –Quadratic * – – – – –

ME × CP * – – – – –ME × CP (linear) * – – – – –ME × CP (quadratic) * – – – – –

1Grams per 100 g of live weight.2, 3, and 4Standard error of means of ME, CP and ME × CP, respectively.*P≤0.05.**P≤0.01.***P≤0.001.

3.2. Carcass responses

Quadratic effects of dietary CP as CP × ME interactions were found on carcass yieldof birds reared in hot climate. Improvement in breast weight was noted on low ME dietswith moderate dietary CP (Table 3). A linear effect of dietary CP was noted on breastyield.

It was observed that dietary ME levels had a significant effect on the abdominal fatpad. A high correlation coefficient (P<0.002) of 0.67 was observed between dietary MEand abdominal fat pad. No effect of dietary CP was observed on abdominal fat pad. Theresults indicated that abdominal fat did not significantly increase with decreased in dietaryCP level if low protein diets were supplemented with essential amino acids. No significant

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differences were noted for heart, liver and gizzard weights of broiler birds fed differentexperimental diets except for increased liver weight with increasing dietary ME. Resultsindicated that ME had no effect on carcass, breast, heart and gizzard weights of the birds.

3.3. Carcass composition

Significantly reduced dry matter (DM) and increased CP and fat contents of carcasswere noted with increasing dietary ME levels. A linear effect of increasing dietary CP wasobserved on carcass fat, whereas the effect was quadratic on DM, and CP contents (Table 4).High ME and high CP diet increased the carcass fat and CP contents and reduced the carcassDM contents. No effect of dietary ME, CP or their interaction was noted on mineral (ash)contents of the carcass.

Table 4Effect of dietary energy and protein levels on meat composition (as such basis) of the broilers kept in heat stressenvironment (g/kg)

Dry matter Crude protein Fat Ash

ME (MJ/kg)12.13 423 241 174 10.112.55 421 246 180 10.2SEM1 0.18 0.15 0.11 0.03

CP (g/kg)190 422 239 176 10.1210 421 241 176 10.1230 423 250 178 10.2SEM2 0.23 0.18 0.13 0.04

ME × CP12.13 × 190 423 236 172 10.012.13 × 210 421 239 173 10.212.13 × 230 424 248 176 10.112.55 × 190 421 241 179 10.212.55 × 210 421 246 179 10.112.55 × 230 421 252 180 10.2SEM3 0.32 0.26 0.19 0.06

SignificanceME *** *** *** –

CP *** *** *** –Linear *** ** * –Quadratic *** ** – –

ME × CP ** ** ** –ME × CP (linear) ** ** * –ME × CP (quadratic) ** ** ** –

1, 2, and 3Standard error of means of ME, CP and ME × CP, respectively.* P≤0.05.

** P≤0.01.*** P≤0.001.

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4. Discussion

High ambient temperature is generally detrimental to birds which results in reducedFI and subsequently depress BWG and F:G. Kamran et al. (2004) noted non-significanteffect of energy and protein dilution on FI that verified the findings of the present study.Similarly, Han et al. (1992) noted no differences in FI of broilers when CP contents ofthe diet were decreased from 230 to 210 g/kg. Bartov and Plavnik (1998) reported similarresults in terms of FI until 42 days of age in broilers fed diets with low and recommendedCP level. However, the results of the present findings are not in agreement with those ofLeeson et al. (1996), Cheng et al. (1997) and Nawaz et al. (2006). They reported increasedFI with the reduction in dietary ME. Similarly, Ferguson et al. (1998) and Bregendahl etal. (2002) also reported a significant increase in FI in broiler chicks fed 200 g CP/kg ofdiets supplemented with amino acids than those fed diets containing 230 g CP/kg. They,however, did not study the effect of ME on FI in high temperature environments. Birdsgenerally eat for calories and during period of high temperature, the FI is not great enoughto satisfy their energy requirements. The increase in dietary ME is one of the possibleways to fulfil the bird’s energy requirements during periods of high ambient tempera-ture. This may be the possible reason why FI was not affected by dietary ME levels.The heat increment for protein is much higher when the birds’ ambient temperature ishigh than when it is low. The levels of dietary protein or amino acids also stimulatesprotein turnover that result in more metabolic heat production (Mushraf and Latshaw,1999).

Low CP and high ME diets also improved the BW gain. Kamran et al. (2004) reportedimprovement in BWG when CP of the diet was reduced from 230 to 210 g/kg in a hotenvironment. High CP with low ME in the present study resulted in reduced BW gainprobably due to less energy being available to excrete metabolites of protein catabolism.The results of the present study confirm the findings of Cheng et al. (1997) who reportedadverse effect of feeding high CP diet to heat-stressed broilers on BW gain. However,the results of the present study did not agree with Ferguson et al. (1998) who reportedthat reduction in the CP contents of the diet did not affect the live weight gains ofbroiler chicks from hatching to 21 days. However, they did not conduct their studyduring the periods of high ambient temperature. Dirain and Waldroup (2002) observedthat the increase in the dietary CP could be more detrimental to heat-stressed broil-ers due to the higher heat increment associated with protein metabolism. The presentstudy demonstrated that high dietary CP is detrimental in hot environment with lowenergy diets.

The dietary CP had quadratic effect on F:G in the present study. Moran et al. (1992)found that F:G significantly increased when CP was decreased from 230 to 210 g/kg and210 to 170 g/kg in the starter and grower diets of broiler when the essential amino acids weresupplemented. In the present study, however, dietary CP was not reduced to as much as wasdone by Moran et al. (1992). The results of the present study did not confirm the findingsof Hulan and Proudfoot (1981) who noted better F:G as a result of decreasing protein level.Ferguson et al. (1998), Bregendahl et al. (2002) and Zarate et al. (2003) also observed animprovement in F:G in broiler chicks fed on diets with CP contents reduced from 230 to190 g/kg and supplemented with essential amino acids in hot summer months. Han et al.

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(1992), Bartov and Plavnik (1998) and Kamran et al. (2004) reported no difference in F:G ofbroilers when CP contents of the diets were decreased from 230 to 210 g/kg. The differencein F:G may be due to difference in temperature, broiler strain, type of diet, housing andmanagement conditions etc.

The carcass and breast weights were not affected when the dietary CP was reduced.The results of the present study are in accordance with the findings of Moran et al. (1992)and Leeson et al. (1996) who observed only a small effect of energy and protein dilutionon carcass and breast yields. Kamran et al. (2004) reported an improvement in carcassyield in low CP diets due to reduced heat increment associated with the metabolism ofexcessive protein, which led to reduced heat stress, and, therefore, improved feed utiliza-tion. It seems that low CP slightly increased the digestibility of amino acids required forcarcass formation. Similarly, Bartov and Plavnik (1998) reported an increase in carcassyield on low protein diet at 51 days of age. Holsheimer and Veerkamp (1992) also foundsignificantly increased carcass yield with normal CP but high lysine diet as compared tohigh CP but normal lysine diet. The response of carcass weights to low CP diets mightbe due to better utilization of protein. Similarly, Fancher and Jenson (1989) reported nodifference in breast meat yield when female broilers were given minimum essential aminoacids levels in 159 and 183 g/kg CP diets from 3 to 6-week of age. Kerr and Kidd (1999)concluded that lowering the dietary CP with essential amino acids supplementation resultedin breast meat yield similar to those birds fed on control diet. Similarly, Zarate et al. (2003)reported that reducing CP as compared to industry standards reduced breast meat yield sig-nificantly in summer-reared broilers, and even the essential amino acids supplementationin 10% excess of the industry standards had not any detectable influence on breast meatyield.

Abdominal fat and liver weights increased with increasing dietary ME in the presentstudy. Han et al. (1992) and Kamran et al. (2004) also reported non-significant differencesin abdominal fat pad of broiler birds fed low protein diets supplemented with essentialamino acids. Similarly, Nawaz et al. (2006) reported no effect of CP and/or ME on ediblecarcass characteristics or abdominal fat weight. However, Cheng et al. (1997) reported asignificant decrease in abdominal fat with increase in dietary CP level. Similarly, Si et al.(2004) reported significant increase in abdominal fat pad with decrease in the dietary CPlevel. It seems that, in high CP diets, the energy usage for nitrogen excretion increased andhence it is not deposited as abdominal fat and vice versa.

In general, increases in dietary CP resulted in increased dry matter, CP and fat contentsof carcass whereas dietary ME increased CP and fat contents and decreased dry mattercontent of carcass. However, the differences among the various experimental diets were notgreat. Parr and Summers (1991) reported that chicks fed low protein diets (ranging from 165to 210 g CP/kg supplemented with essential amino acids) had similar total carcass proteincontents as those fed a 230 g/kg dietary CP. Neto et al. (2000) noted that breast muscleprotein was not significantly affected when a low protein diet (170 g/kg) supplemented withessential amino acids and methionine was fed to the broilers as compared to a 240 g CP/kgdiet. However, this area needs further investigations.

It can be concluded from the results of the present study that reducing dietary CP inthe diets of birds reared in hot climate had a little effect on the growth performance of thebroilers.

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References

AOAC, 1990. Official Methods of Analysis, 15th ed. Association of Analytical Chemist, Arlington, Virginia.Bartov, I., Plavnik, I., 1998. Moderate excess of dietary protein increases breast meat yield of broiler chicks. Poult.

Sci. 77, 680–688.Bregendahl, K., Sell, J.L., Zimmerman, D.R., 2002. Effects of low protein diets on growth performance and body

composition of broiler chicken. Poult. Sci. 81, 1156–1167.Cheng, T.K., Hamre, M.L., Coon, C.N., 1997. Responses of broilers to dietary protein levels and amino

acid supplementation to low protein diets at various environmental temperatures. J. Appl. Poult. Res. 6,18–33.

Daghir, N.J., 1983. Effect of lysine and methionine supplementation of low protein roaster diets fed after six weeksof age. Poult. Sci. 62, 572–575.

Dirain, C.P., Waldroup, P.W., 2002. Protein and amino acid needs of broilers in warm weather: a review. Int. J.Poult. Sci. 1, 40–46.

Fancher, B.I., Jenson, L.S., 1989. Dietary protein level and essential amino acids contents: Influence upon femalebroiler performance during the grower period. Poult. Sci. 68, 897–908.

Ferguson, N.S., Gates, R.S., Taraba, J.L., Cantor, A.H., Pescatore, A.J., Ford, M.J., Burnham, D.J., 1998. Theeffect of dietary protein and phosphorus on ammonia concentration and litter composition in broilers. Poult.Sci. 77, 1085–1093.

Han, Y., Suzuki, H., Parsons, C.M., Baker, D.H., 1992. Amino acid fortification of a low protein corn and soybeanmeal diet for chicks. Poult. Sci. 71, 1168–1178.

Holsheimer, J.P., Jensen, W.M.M.A., 1991. Limiting amino acids in low protein maize-soybean meal diets fed tobroiler chicks from 3 to 7 week of age. Poult. Sci. 32, 141–158.

Holsheimer, J.P., Veerkamp, C.H., 1992. Effect of dietary energy, protein, and lysine content on performance andyields of two strains of male broiler chicks. Poult. Sci. 71, 872–879.

Hulan, H.W., Proudfoot, F.G., 1981. The effect of different dietary protein levels in a three-stage diet system ongeneral performance of chickens reared to roaster weight. Poult. Sci. 60, 172–178.

Hurby, M., Hamre, M.L., Coon, C.N., 1995. Predicting amino acids requirements for broilers at 21.1 ◦C and32.2 ◦C. J. Appl. Poult. Res. 4, 395–401.

Hurwitz, S., Weiselberg, M., Eisner, U., Bartov, I., Riesenfield, G., Shareit, M., Nir, A., Bornstein, S., 1980.The energy requirements and performance of growing chickens and turkeys as affected by environmentaltemperature. Poult. Sci. 59, 2290–2299.

Jennsen, L.S., Colnago, G.L., 1991. Amino acids and proteins for broilers and laying hens. In: Proceeding ofMaryland Nutrition Conference of Feed Manufacturer, Baltimore. MD, USA, pp. 29–36.

Kamran, Z., Mirza, M.A., Haq, A.U., Mahmood, S., 2004. Effect of decreasing dietary protein levels with optimumamino acids profile on the performance of broilers. Pak. Vet. J. 24, 165–168.

Kerr, B.J., Kidd, M.T., 1999. Amino acid supplementation of low-protein broiler diets. l-Glutamic acid andindispensable amino acid supplementation. J. Appl. Poult. Res. 8, 298–309.

Leeson, S., Caston, L., Summers, J.D., 1996. Broiler response to energy or energy protein dilution in finisher diet.Poult. Sci. 75, 522–528.

Moran Jr., E.T., Busnong, R.D., Bilgili, S.F., 1992. Reducing dietary crude protein for broilers while satisfyingamino acid requirements by least cost formulation: live performance, litter composition and yield of fast foodcarcass cuts at 6 weeks. Poult. Sci. 71, 1687–1694.

Mushraf, N.A., Latshaw, J.D., 1999. Heat increment as affected by protein and amino acid nutrition. World’s Poult.Sci J. 55, 233–239.

Nawaz, H., Mushtaq, T., Yaqoob, M., 2006. Effect of varying levels of energy and protein on live performanceand carcass characteristics of broiler chicks. J. Poult. Sci. 43, 388–393.

Neto, M.G., Pesti, G.M., Bakalli, R.I., 2000. Influence of dietary protein level on the broiler chicken’s responseto methionine and betaine supplements. Poult. Sci. 79, 1478–1484.

Parr, J.F., Summers, J.D., 1991. The effect of minimizing amino acid excesses in broiler diets. Poult. Sci. 70,1540–1549.

Pourrreza, J., Edriss, M.A., 1992. The effects of high vs. normal temperatures on the physical characteristics ofthe broilers carcass. J. Agric. Sci. Technol. 1, 35–41.

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312 Q.U. Zaman et al. / Animal Feed Science and Technology 146 (2008) 302–312

Rahman, M.S., Pramanic, A.H., Basak, B., Tarafdar, S.U., Biswas, S.K., 2002. Effect of feeding low protein dietson the performance of broilers during hot humid season. Int. J. Poult. Sci. 1, 35–39.

Reece, F.N., Dearon, J.W., Kubena, L.F., 1972. Effects of high temperature and humidity on heat prostration ofbroiler chickens. Poult. Sci. 48, 269–277.

Si, J., Fritts, C.A., Burnham, D.J., Waldroup, P.W., 2004. Extent to which crude protein may be reduced incorn-soybean meal broiler diets through amino acid supplementation. Int. J. Poult. Sci. 3, 46–50.

Smith, M.O., Teeter, R.G., 1987. Effects of potassium chloride and fasting on broiler performance under simu-lated summer conditions. Animal Science Research Report, Agriculture Experiment Station, Oklahoma StateUniversity. MP-119, pp. 161–164.

Sterling, K.G., Pesti, G.M., Bakalli, R.I., 2003. Performance of broiler fed various levels of dietary lysine andcrude protein. Poult. Sci. 82, 1939–1947.

Teeter, R.G., Belay, T., 1996. Broiler management during acute heat stress. Anim. Feed Sci. Technol. 58, 127–142.Zarate, A.J., Moran Jr., E.T., Burnham, D.J., 2003. Reducing crude protein and increasing limiting essential amino

acid levels with summer reared, slow and fast feathering broilers. J. Appl. Poult. Res. 12, 160–168.