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UNIVERSITI PUTRA MALAYSIA
EFFECTS OF L-LEUCINE SUPPLEMENT ON THE GROWTH PERFORMANCE AND CARCASS CHARACTERISTICS OF
GROWER- FINISHER BROILERS FED WITH VARYING LEVELS OF PROTEIN AND ENERGY
EDI ERWAN ITA 2009 1
EFFECTS OF L-LEUCINE SUPPLEMENT ON THE GROWTH
PERFORMANCE AND CARCASS CHARACTERISTICS OF
GROWER- FINISHER BROILERS FED WITH VARYING
LEVELS OF PROTEIN AND ENERGY
By
EDI ERWAN
Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia
in Fulfilment of the Requirements for the Degree of Master of Science
October 2009
ii
DEDICATION
I wish to dedicate this thesis to my beloved family, my wife Susi
Fitria, who always understand and give me loving support. My sons
Muhammad Jilan Naufal, Muhammad Dzaki Manaf dan
Muhammad Faiz Ramadhan
iii
Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment
of the requirement for the degree of Master of Science
EFFECTS OF L-LEUCINE SUPPLEMENT ON THE GROWTH
PERFORMANCE AND CARCASS CHARACTERISTICS OF
GROWER- FINISHER BROILERS FED WITH VARYING
LEVELS OF PROTEIN AND ENERGY
By
EDI ERWAN
October 2009
Chairman : Professor Abdul Razak Alimon, PhD
Faculty/Institute : Institute of Tropical Agriculture
Four studies were conducted to determine the effects L-leucine supplementation on
the growth performance and carcass characteristics of grower-finisher chickens fed
diets containing different levels of crude protein (CP) and metabolizable energy
(ME). Experiment 1 utilized a series of 4 diets that were formulated to contain ME
levels (3200 Kcal/kg or 3000 Kcal/kg) and supplemented with two levels of L-
leucine either 0 or 0.5%. In Exp. 1, 80 Cobb broilers were used to examine the
effect of L-leucine supplementation on growth performance and carcass
characteristics fed different levels of energy. There was no interaction between the
dietary levels of L-leucine and ME. The supplementation 0.5% of L-leucine had no
significant effect on FI, WG and FCR but significant increased in carcass weight up
to 9% was observed. The decrease in ME from 3200 to 3000 kcal/kg also did not
iv
affect FI and FCR, but WG decreased up to 7.4%. Similarly, reducing ME had no
significant effect on carcass composition and sensory characteristics.
Exp. 2, The effect of the growth performance and sensory characteristics in reducing
CP supplemented by L-leucine. A series of 6 diets that were formulated to contain
CP levels of 20 and 18% at each of three levels of L-leucine supplementation (0, 0.5
and 0.67%). Treatments were applied to Cobb 180 broilers distributed across 36 floor
pens with 5 chicks per pen while the parameters measured and procedures were
similar to experiment 1. There was no interaction between the level of L-leucine
supplementation and CP levels. FI, WG and FCR were not affected with increasing
levels of L-leucine supplementation. Breast meat yield in numerically increased
when added by L-leucine to a level of 0.5%. However a significant decrease of breast
meat obtained when added with L-leucine to a level reached 0.67%. Similarly, the
sensory analysis indicated no significant differences in tenderness, juiciness, flavor,
aroma, and overall acceptability. Bone and lean were not affected with increasing
levels of L-leucine supplementation. Fat was decreased (P<0.05), when leucine was
added at 0.5%.
In experiment 3, four experimental diets were formulated with added L-leucine with
dietary levels as follow: D1 (control, ME 3200 kcal/kg; 20% CP without additional
of L-leucine), D2 (ME 3000 kcal/kg; 18% CP added by 0.5% L-leucine), D3 (ME
3000 kcal/kg; 18% CP added by 0.67% L-leucine) and D4 (ME 3000 kcal/kg; 20%
CP added by 0.75% L-leucine). Chickens fed excessive levels of leucine grown at a
significantly slower rate than the control, whereas addition of 0.5% L-leucine caused
the greatest depression. Similarly, the growth depression accompanied by significant
worsened of FCR. In contrast, breast meat increased (P<0.01) as supplementation of
v
low CP and ME with L-leucine, whereas level of 0.67% was the maximum weight.
Furthermore, heart was not affected (P>0.05). Supplementation of L-leucine
significantly (P<0.01) decreased lean, bone and fat compared to control.
In Exp. 4, four experimental diets were formulated with added L-leucine with
constant level as follows: D1 (control, ME 3200 kcal/kg; 20% CP without additional
of L-leucine), D2 (ME 3000 kcal/kg; 16% CP added by 0.5% L-leucine), D3 (ME
3000 kcal/kg; 18% CP added by 0.5% L-leucine) and D4 (ME 3000 kcal/kg; 20% CP
added by 0.5% L-leucine). FI was not significantly affected by the treatments but
BWG decreased as CP decreased and supplementations with L-leucine did not
ameliorate this effect. Similarly, supplementation of L-leucine in low CP worsened
FCR. Live weight, carcass, abdominal fat, gizzard and liver decreased (P<0.05) as
supplementation in low CP with L-leucine compared to control diet. In contrast,
breast meat increased (P<0.01) as supplementation of low CP with L-leucine. In
conclusion, L-leucine supplementation up to 0.67% either in 2% decrease of CP or
3000 Kcal/kg ME did not affect the growth performance and sensory characteristic.
Supplementation of L-leucine up to 0.5% in diets tend to increase carcass weight
and breast meat. Lowering CP level than 2% seems worthwhile for slow growing
broiler in grower-finisher period and induced fat deposition.
vi
Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai
memenuhi keperluan untuk ijazah Master of Science
EFFECTS OF L-LEUCINE SUPPLEMENT ON THE GROWTH
PERFORMANCE AND CARCASS CHARACTERISTICS OF
GROWER- FINISHER BROILERS FED WITH VARYING
LEVELS OF PROTEIN AND ENERGY
Oleh
EDI ERWAN
JUNE 2009
Pengerusi : Professor Abdul Razak Alimon, PhD
Fakulti/Institut: Institut Pertanian Tropika
Empat eksperimen telah dijalankan bagi menentukan kesan L-leucine sebagai
makanan tambahan atas prestasi pertumbuhan dan ciri-ciri karkas yang meliputi
komposisi badan, ciri-ciri sensori ayam pembesaran-penamat (grower-finisher).
Ternakan ini diberi diberikan makanan yang mempunyai aras protein kasar dan
tenaga metabolise (ME) yang berbeza. Dalam eksperimen 1 menggunakan 4
kombinasi makanan yang mengandung aras ME 3,200 dan 3,000 Kcal/kg, masing-
masing diberikan 0 atau 0.5% L-leucine telah dikaji. Eksperimen ini menggunakan
80 ekor baka Strain Cobb yang dipelihara dalam 16 reban dengan 5 ekor setiap
reban. Penambahan L-leucine hingga 0.5% tiada mempengaruhi prestasi
pertumbuhan namun secara signifikan meningkatkan karkas sehingga 9%.
Pengurangan ME daripada 3,200 kepada 3,000 kcal/kg juga tidak memberi kesan
terhadap pengambilan makanan dan kecukupan makanan, namun berat badan
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menurun hingga 7.4%. Pengurangan ME tidak memberi kesan terhadap komposisi
karkas dan ciri-ciri sensori.
Eksperimen 2 bertujuan untuk menilai kesan pengurangan protein yang ditambahkan
L-leucine terhadap prestasi dan sifat-sifat karkas. 6 jenis diet yang mengandung 2
aras protein kasar (20 dan 18%) dan 3 aras penambahan L-leucine (0, 0.5 and
0.67%). Eksperimen ini menggunakan 180 ekor ayam pedaging baka Cobb yang
ditempatkan pada 36 buah reban dengan 5 ekor setiap reban. Parameter dan kaidah
pengukurannya adalah sama dengan eksperimen 1. Pengambilan makanan,
pertambahan berat badan dan FCR tidak dipengaruhi dengan peningkatan aras
pemberian L-leucine. Hasil daging dada didapati meningkat dengan penambahan
leucine pada aras 0.5% didalam diet. Namun begitu penurunan yang signifikan telah
dilihat apabila penambahan arasnya ditingkatkan kepada 0.67% dalam makanan.
Penambahan L-leucine tidak memberi kesan terhadap ciri-ciri sensori, begitu juga
dengan berat tulang dan daging. Kandungan lemak berkurang apabila leucine
ditambah pada aras 0.5%.
Dalam eksperimen 3, empat makanan ternak diformulasikan dengan diberi beberapa
aras L-leucine. D1 (sebagai kawalan. mengandungi ME 3,200 kcal/kg, 20% CP
tanpa penambahan L-leucine), D2 (3000 kcal/kg; 18% CP dengan penambahan 0.5%
L-leucine), D3 (ME 3000 kcal/kg; 18% CP dengan penambahan 0.67% L-leucine)
dan D4 (ME 3000 kcal/kg; 20% CP dengan penambahan 0.75% L-leucine).
Eksperimen ini menggunakan 100 ekor ayam. Ayam yang di beri lebih banyak L-
leucine ternyata lebih lambat membesar dibandingkan dengan kumpulan kawalan,
Manakala penambahan L-leucine pada aras 0.5% menyebabkan penurunan lemak
viii
tertinggi. Walau bagaimanapun, hasil daging dada meningkat dengan penambahan
L-leucine apabila pemberian L-leucine pada aras 0.67% memberi hasil tertinggi
dibandingkan dengan aras-aras yang lain. Selanjutnya, berat jantung tidak
dipengaruhi oleh penambahan L-leucine.
Dalam eksperimen ke 4, empat makanan diformulasikan dengan penambahan L-
leucine pada aras yang tetap (0.5%). Susunan makanan adalah seperti berikut: D1
(sebagai kawalan mengandungi ME 3,200 kcal/kg, 20% CP tanpa penambahan L-
leucine), D2 (3000 kcal/kg; 18% CP dengan penambahan 0.5% L-leucine), D3 (ME
3000 kcal/kg; 16% CP dengan penambahan 0.5% L-leucine) dan D4 (ME 3000
kcal/kg; 20% CP dengan penambahan 0.5% L-leucine). Eksprimen ini menggunakan
60 ekor ayam. Tidak ada kesan perlakuan terhadap pengambilan makanan. Walau
bagaimanapun berat badan didapati menurun dengan berkurangnya aras protein.
Penambahan L-leucine saja tidak meningkatkan prestasi pertumbuhan ayam
dibandingkan dengan kumpulan kawalan. Berat hidup, karkas, lemak abdomen,
empedal dan hati menurun sejalan dengan penambahan L-leucine pada makanan
berprotein rendah jika dibandingkan dengan kumpulan kawalan.
Sebagai kesimpulan, bahwa penambahan L-leucine sehingga ke aras 0.67% tidak
memberi kesan terhadap prestasi dan ciri-ciri sensori sama ada di dalam makanan
yang dikurangkan 2% aras proteinnya, ataupun pengurangan tenaga metabolismenya
menjadi 3000 kcal/kg.
Penambahan L-leucine pada aras 0.5% di dalam makanan memberi kecenderungan
ke arah peningkatan berat karkas and daging dada. Pengurangan protein melebihi
ix
2% akan mengakibatkan penurunan kadar pertumbuhan ayam pedaging disamping
menggalakkan penimbunan lemak yang lebih banyak.
x
ACKNOWLEDGEMENTS
I would like to express my utmost gratitude to my highly respected supervisor,
Professor Dr. Abdul Razak Alimon, Chairman of the supervisory committee for
giving me the opportunity to work on this wonderful project and his invaluable
guidance, advice, support, and encouragement throughout the period of the study.
I wish to express my heartfelt thankfulness to Assoc. Professor Dr. Halimatun
Yaakub and Dr Awis Qurni Sazili of members of supervisory committee for their
suggestions and guidance towards the completion of this study.
Deepest thanks is due to Rector Professor Dr. H.M Nazir, MA, Vice Rector for
Academic, Professor Dr. Munzir Hitami, MA, Dean of Agriculture and Animal
Science faculty, Dr. Tantan R. Wiradarya, MSc, State Islamic University of Suska,
Riau, Indonesia for allowing me the study leave and his willingness to support on all
of my duties while I was abroad.
My special gratefulness is also addressed to all staff of Nutrition Laboratory: Mr.
Saparin and Mr. Zakaria; Poultry Farm staff : Mr. Mazlan and Mr. Ponusami for their
help and working in such a nice environment during the completion of my study.
My appreciations are also due to my parents, (Allahyarham) Kusniadi and Hajjah
Tumiyam for their undying love and upbringing, my brothers Arifin K and Rahmad
and sisters Esprapti, drh. Susilawati, MM and Soleha, S.Pd for their constant
encouragement and support during the course of the study.
xi
Very special thanks and appreciation to my wife, Susi Fitria,S.E, and lovely boys
Muhammad Jilan Naufal, Muhammad Dzaki Manaf and Muhammad Faiz Ramadhan
for their moral support, encouragement, patience, love and understanding.
Last but not least, I would like to thank to Muhammad Afdal, Muhammad Malik,
Abdoreza Soleimani Farjam, Norbaiyah Binti Bahyuddin, Tang Siew Ching, Abdel
Rahim Abubakar, Nurbaiyah, Hamidah, Muhammad Ramin for their encouragement
throughout my study.
xii
I certify that an Examination Committee met on June 2008 to conduct the final
examination of Edi Erwan on his Master thesis entitled” Effects of L-Leucine
Supplement on The Growth Performance and Carcass Characteristics of Broilers
Chicken Fed with Varying Protein and Energy Levels’ in accordance with
Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian
Malaysia(Higher Degree) Regulation 1981. The Committee recommends that the
candidate be awarded the relevant degree.
Members of Examination Committee are as follows:
Ismail Idris, PhD
Associate Professor
Faculty of Agriculture
Universiti Putra Malaysia
(Chairman)
Loh Tech Chwen, PhD
Associate Professor
Faculty of Agriculture
Universiti Putra Malaysia
(Member)
Engku Azahan, PhD
Associate Professor
Faculty of Veterinary Medicine
Universiti Putra Malaysia
(Member)
Wan Zahari Mohamed, PhD
Director
Strategic Livestock Research Center
MARDI, Serdang
(External examiner)
______________________________
HASANAH MOHD. GAZALI, PhD
Professor/Deputy Dean
School of Graduate Studies
Universiti Putra Malaysia
xiii
This thesis is submitted to the Senate of Universiti Putra Malaysia and has been
accepted as fulfillment of the requirement for the degree of Master of Science. The
members of the supervisory Committee as follows:
Abdul Razak Alimon, Ph.D
Professor
Faculty of Agriculture
Universiti Putra Malaysia
(Chairman)
Halimatun Yaakub, Ph.D
Associate Professor
Faculty of Agriculture
Universiti Putra Malaysia
(Member)
Awis Qurni Sazili, Ph.D
Lecturer
Faculty of Agriculture
Universiti Putra Malaysia
(Member)
______________________________
HASANAH MOHD GAZALI Ph.D
Professor / Dean
School of Graduate Studies
Universiti Putra Malaysia
Date: 14/1/2010
xiv
DECLARATION
I declare that the thesis is my original work except for quotations and citations which
have been duly acknowledged. I also declare that it has not been previously, and is
not concurrently, submitted for any other degree at University Putra Malaysia or at
any other Institution.
E D I E R W A N
Date: 4/9/2009
xv
TABLE OF CONTENTS
Page
ABSTRACT iii
ABSTRAK vi
ACKNOWLEDGEMENTS x
APPROVAL xii
DECLARATION xiv
LIST OF TABLES xviii
LIST OF FIGURES xix
LIST OF ABBREVIATIONS xx
CHAPTER
1 INTRODUCTION 1
2 LITERATURE REVIEW 3
2.1. Protein in Broiler Rations 3
2.2. Energy in Broiler Ration 4
2.3. Leucine Requirement of Broilers 6
2.4. Carcass Characteristics 10
2.5. Sensory Analysis 13
2.5.1. Flavor and Aroma 15
2.5.2. Tenderness 16
2.5.3. Juiciness 17
2.6. Category Scales 17
3 MATERIALS AND METHODS 19
3.1. Experiment 1. 19
3.2. Experiment 2. 20
3.3. Experiment 3. 20
3.4. Experiment 4. 21
4 EFFECT OF VARYING LEVELS OF LEUCINE
AND ENERGY ON PERFORMANCE AND
CARCASS CHARACTERISTICS OF BROILER
CHICKENS
Abstract 22
4.1. Introduction 23
4.2 Materials and Methods 24
4.3. Results and Discussion 26
References 31
Copyright Permission/Acceptance letter 33
xvi
5 EFFECTS OF VARYING LEVELS OF L-LEUCINE
AND METABOLIZABLE ENERGY IN FINISHER
DIET ON CARCASS COMPOSITION AND MEAT
SENSORY CHARACTERISTICS OF BROILER
CHICKENS
Abstract 34
5.1. Introduction 35
5.2. Materials and Methods 35
5.2.1. Pysical Carcass Composition 37
5.2.2. Sensory evaluation 38
5.3. Results and Discussion 39
References 45
Copyright Permission/Acceptance letter 48
6 EFFECT OF LEUCINE SUPPLEMENTATION ON
GROWTH PERFORMANCE, CARCASS AND
SENSORY CHARACTERISTICS OF GROWER-
FINSHER BROILER FED VARYING PROTEIN
LEVELS
6.1. Introduction 49
6.2. Materials and Methods 51
6.2.1. Husbandry and Facilities 51
6.2.2. Diet Formulation and Treatments 51
6.2.3. Data Collection and Statistical Analyses 52
6.2.4. Growth Performance 53
6.2.5. Carcass Characteristics and Physical carcass
Composition 53
6.2.6. Sensory Characteristics by Consumer Panel 53
6.3. Results 53
6.3.1. Growth Performance 54
6.3.2. Relative Organ eight and Carcass Characteristics 55
6.3.3. Physical Carcass Composition 57
6.3.4. Sensory Characteristics by Consumer Panel 58
6.4. Discussion 60
7 EFFECT OF DIETARY EXCESS OF L-LEUCINE
ON GROWTH PERFORMANCE AND CARCASS
CHARACTERISTICS OF BROILER
CHICKENS FED LOW PROTEIN AND ENERGY
7.1. Introduction 65
7.2. Materials and Methods 67
7.2.1. Husbandry and Facilities 67
7.2.2. Diet Formulation and Treatments 67
7.2.3. Data Collection and Statistical Analyses 68
7.2.4. Growth Performance 69
7.2.5. Carcass Characteristics and Physical carcass
Composition 69
xvii
7.3. Result 69
7.3.1. Growth Performance 69
7.3.2. Carcass Characteristics 70
7.3.3. Carcass Composition 71
7.4. Discussion 71
8 LEUCINE SUPPLEMENTATION OF LOW CP
IN GROWER-FINISHER BROILER DIETS ON
GROWTH PERFORMANCE AND CARCASS
CHARACTERISTICS
8.1. Introduction 75
8.2. Materials and Methods 76
8.2.1. Experimental Facility 76
8.2.2. Experimental Design and Animal Husbandry 77
8.2.3. Dietary Treatments 77
8.2.4. Growth Performance 79
8.2.5. Carcass Characteristics and Composition
Measurements 79
8.3. Results 80
8.3.1. Growth Performance 80
8.3.2. Carcass Characteristics 80
9.3.3. Carcass Composition 81
8.4. Discussion 82
9 GENERAL DISCUSSION 85
REFERENCES 90
APPENDICES 100
BIODATA OF STUDENT 105
LIST OF PUBLICATIONS 106
LIST OF AWARDS 108
xviii
LIST OF TABLES
Table Page
2.1 Three-stage feeding program in broilers (NRC, 1994) 4
2.2 Classification of amino acids 7
2.3 Amino acid requirements of broilers as percentage of diet 8
4.1 Composition (%) and nutrient content of diets with different
level of leucine and energy in experiment
26
4.2 Weight gain, feed intake, and feed conversion rate as affected by
L- leucine supplementation and energy levels (21-42d)
27
4.3 Final carcass characteristics of broiler fed diets as affected by L-
leucine supplementation and energy levels (42 days of age)
28
5.1 Composition and nutrient content (%) of experimental diets. 39
5.2 Carcass characteristics of broiler chickens fed diets
supplemented with L-leucine and at two energy levels (42 days
of age)
43
5.3 Sensory acceptance of chicken meat characteristics as affected
by L- leucine supplementation and energy levels (21-42d)
44
6.1 Composition (%) and nutrient content of experimental diets 52
6.2 Weight gain, feed intake and feed conversion ratio (FCR) of
broilers fed diets with two levels of protein and supplemented
with L-leucine from day 21 to day 42.
54
6.3 Weights (g) of Carcass, abdominal fat, breast meat, gizzard, liver
and heart of broiler fed diets supplemented with L-leucine with
two levels of protein at 42 days of age
56
6.4 Carcass composition of broiler fed diets as affected by L-leucine
supplementation and protein levels (42 days of age)1 (mean ±
standard deviation)
57
6.5 Chicken meat sensory characteristics rate as affected by L-
leucine supplementation and protein levels (21-42d) (mean ±
standard deviation)
59
7.1 Percentage inclusion and calculated composition of the test diets
in experiment
68
7.2 Effect of dietary treatments on growth performance of grower-
finisher broiler chickens from 21 to 42 days
70
7.3 Final carcass characteristics of broiler fed diets as affected by L-
leucine supplementation and energy levels (42 days of age)
70
7.4 Final carcass composition of broiler fed diets as affected by L-
leucine supplementation and protein levels (42 days of age)
71
8.1 Percentage inclusion and calculated composition of the test diets
in experiment
78
8.2 Weight gain (g), feed intake (g) and FCR (g/g) of broilers as
influenced Dietary levels of Protein*
80
8.3 Final carcass characteristics of broiler fed diets as affected by
Protein levels (42 days of age)
81
8.4 Final carcass composition of broiler fed diets as affected by L-
leucine supplementation (42 days of age)
82
xix
LIST OF FIGURE
Figure Page
1. Steps of testing order on Sensory Test 102
xx
LIST OF ABBREVIATIONS
wk Week
d Day
BCAAs Branched Chain Amino Acids
hr Hour
cal Calorie
kcal Kilo Calorie
g Gram
kg Kilogram
BWG Body Weight Gain
CP Crude Protein
FI Feed intake
FCR Feed Conversion Ratio
ME Metabolizable Energy
FCR Feed Conversion Ratio
EAA Essential Amino Acids
NRC National Research Center
Glu Glumatic Acid
E:P Energy: Protein
WHC Water Holding Capacity
AOAC Association of Official Analytic
Chemist
WG Weigh Gain
CHAPTER 1
INTRODUCTION
Proteins are organic compounds made up of 22 different amino acids (AA) or
derivates arranged in a linear chain and linked together by peptide bonds between the
carboxyl and amino groups of adjacent AA residues. These nutrients also work
together to achieve a particular function, and they are often associated to form stable
complexes (Maton et al., 1993). Crude protein (CP) is the most crucial nutrient in
determining feed cost in the poultry production (Witjetten et al., 2004a). Excessive
CP in the diet will affect a large portion of diet cost, and may negate economic
returns due to suboptimal growth and meat yields (Kidd et al., 2005). In addition, as
there may be a rule to reduce nitrogen excretion in future, reduction of nitrogen and
phosphorus in animal wastes will be one of the primary choice in the diet
formulation. (Si et al., 2004). Therefore, there is a revenue in broiler production
enterprise that can be managed by changing dietary CP (Eits et al., 2005). The
branched-chain amino acids (BCAAs)-leucine, isoleucine, and valine are essential
nutrients that must be obtained from food (Harper, 1984). These AA play important
roles in protein synthesis and energy production. BCAAs make up 35-40% of the
essential amino acids in body protein and 14% of the total amino acids in skeletal
muscle.
Although many research have been documented which examined the effects of low
CP diets on performance and carcass characteristics, but only a few have described
the effects of supplementing BCAAs, in particular leucine on performance and
2
carcass characteristics of grower-finisher broiler.
Together with amino acids, the metabolizable energy (ME) level in broiler diets play
an important role in determining the growth performance and carcass characteristics
of the birds. When fed ad libitum, broiler chickens will consume sufficient feed to
satisfy their energy requirements and hence, energy level is crucial in determining
dry matter intake. If the energy intake of the broiler changes, so does the intake of
protein. The energy requirement of broiler decreases as the ambient temperature
increase above 21oC. Reduction in energy requirement in chickens is mainly due to
the reduction in requirement for maintenance whereas the energy requirement for
production is not influenced by environmental temperature (Hurwitz et al., 1980).
High energy broiler starter diets result in extra deposition of fat (Holsheimer and
Jensen, 1991) resulting in the wastage of dietary energy. Hence, to achieve optimal
broiler performance especially in tropical environment requires a suitable
combination both of ME and CP. This attempt not only to ensure optimum
utilization of each and every nutrient in the diets and help to reduce the cost of
production and environmental pollution associated with the loss of nitrogen in
excreta. There has been no research conducted with grower-finisher broiler in low
CP or ME diets that supplemented by L-leucine. The present study was therefore
designed to investigate the effect of altering dietary CP and ME on the performance
and carcass characteristics of broiler chickens supplemented L-leucine during
grower-finisher periods.
3
CHAPTER 2
LITERATURE REVIEW
2.1. Protein in Broiler Ration
In general, protein are composed of carbon, hydrogen, oxygen, nitrogen and in some
cases, sulfur. The percentage of nitrogen in protein is on average 16%. Voet et al
(1999) stated that proteins play a role in all biological process because essentially all
molecular transformations in body metabolism are mediated by protein catalyst, or
enzymes. The type and level of dietary protein in animal ration influence the
productivity of farm animals. Proteins are comp long chains of up to 22 amino acids
that are linked together by peptide bonds. Dietary protein content has a great
ef f ect on the growth performance of the birds and is the most expensive
nutrient in broiler diets (Drain and Waldroup, 2002) . Dietary CP is used by
broilers for many functions, the most important being accretion of protein as broiler
meat (Aftab et al., 2006). Hence, the recent issues regarding the environment and the
high cost of protein supplement affect nutritionist to decrease CP levels in diets while
sustaining performance. Since 1950‟s methionine and lysine as supplements have
been successfully used in poultry diets allowing for reduction in CP levels.
Moreover, with the development of additional feed-grade amino acids such as
threonine and tryptophan the chance exists to decrease the CP level in diets even
further since it is commonly agreed that greater performance in chicks can be
achieved if essential amino acids (EAA) in low CP diet equal to those needed in
higher CP diets (Pinchasov, 1990).
4
However, the effects of replacing low CP with several amino acids in broiler diets is
not always consistent ( Bregendahl et al., 2002; Jiang et al., 2005; Si et a., 2004;
Farran et al., 2003). The reason for the failure to achieve the performance with low
protein diets fortified with amino acids are not clearly understood. BCAAs have been
recognized as deleterious to many species when fed in excess (D‟Mello and Lewis,
1970, Farran et al., 2003). Such treatments resulted in depressed food intake and
reduced growth. It was reported that dietary excess of leucine content depressed
weight gain and feed intake during the starter period of broiler chickens (Edmon and
Baker, 1987; Smith and Austic, 1977; Farran and Thomas, 1990; Penz et al., 1984),
but increased carcass weight of growing-broiler chickens (Keer and Kidd, 1999). A
three-stage feeding program of protein requirement during starting, growing and
finishing periods as recommended by the NRC (1994) is shown in Table 2.1.
Table 2.1. Three-stage feeding program in broilers (NRC, 1994)
Three-stage program
Starter Grower Finisher
Age (days) 0-3 3-6 6-8
% protein 23 20 18
Increasing the dietary protein increases carcass protein and reduces carcass fat of
broilers. Little or no improvement in weight is achieved when dietary protein is
raised above 20% (Summers et al., 1968; Brown & McCartney, 1982). Less dietary
protein and more dietary energy was shown by Donaldson et al (1956), to be
required per unit of gain, as the calorie-to protein ratio is increased.
2.2. Energy in broiler rations
Energy is one of the most important factors in broiler diets and plays an important