INFLUENCE OF CHICKEN GROWTH HORMONE GENE ON THE LINEAR MORPHOMETRY AND PRODUCTION PERFORMANCE OF THREE CHICKEN GENOTYPES IN NIGERIA

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INFLUENCE OF CHICKEN GROWTH HORMONE GENE ON THE LINEAR MORPHOMETRY AND PRODUCTION PERFORMANCE OF THREE CHICKEN GENOTYPES IN NIGERIA

ABSTRACT

Recently, there is a trend on the development and improvement of the locally adapted chickens within their environments. This would enable them to withstand the climatic conditions and endemic poultry diseases. The research was conducted in order to characterize the chicken growth hormone (cGH) gene and associate its relationship with linear morphometry and production performances in three genotypes of Nigerian chicken namely: the Funaab Alpha, the Shika Brown and the Local chicken. The study was carried out at the Poultry unit of the Teaching and Research Farms, Federal University of Technology Owerri, Imo-state and Molecular Genetics Laboratory of the Department of Animal Science, University of Port-Harcourt, River-state. The objectives were: 1. To determine the growth, laying performance and egg quality characteristics of the three genotypes. 2. Determine the linear morphometry of the genotypes and to establish the relationships between the linear morphometry, growth, egg quality and laying performance of the chickens. 3. Characterize the cGH gene status of the three genotypes and to establish its relationship with the linear morphometry and production performance of the chickens. A total of two hundred and seventy chickens (ninety per genotype) were used on a three replicate pens of thirty birds each. The birds were sourced at day old, brooded and raised to egg production on deep litter during which data were collected on growth performance index, linear body measurements, egg quality characteristics and laying performance, and genomic analysis for chicken growth hormone gene. Data collected were subjected to analysis of variance of General Linear Model procedure (SAS, 2004). Correlation and Regression were done using Pearson‟s moment correlation of SAS (2004), while significant means were separated using Duncan‟s new multiple range test (Duncan, 1955). Significant differences (P<0.05) were obtained on growth performance index (body weight, weight gain, feed intake and feed conversion ratio) with the Funaab Alpha as the best performed genotype, then the Shika Brown and the local chicken respectively. This suggested that Funaab Alpha is good in meat production. On egg laying and quality characteristics, significant differences (P<0.05) were obtained in most of the traits studied. Shika Brown had the best performance in most traits (egg length and width, egg weight, shell thickness, albumen height, width and length, yolk height and width, shell colour; albumen, yolk and egg shape indices and Haugh unit), then the Funaab Alpha and local breed followed respectively. This finding is suggesting Shika Brown a better breed for egg production while Funaab Alpha could qualify better as dual purpose breed. Significant difference (P<0.05) was also obtained in the linear body measurements. Funaab Alpha had the most performance, then Shika Brown and the Local chicken followed respectively. Highly significant (P<0.01) and positive correlation were obtained between the body weight and linear morphometry, egg weight, egg length, egg width, albumen height, albumen width, albumen length, shell colour, yolk height, yolk width, yolk index, albumen index and shape index; between the shell thickness and egg width, Haugh unit and albumen index, yolk height and yolk width, albumen index. Significant (P<0.05) and positive correlations were found to exist between shell thickness and egg weight, yolk height and Haugh unit, yolk index and albumen index, Non-significant (P>0.05) and positive correlations were also found to exist between the shell colour and shell thickness, yolk index, egg shape index; shell thickness and egg length, albumen width, yolk height, yolk width, shape index; egg weight and Haugh unit, yolk index, egg shape index. Highly significant (P<0.01) and negative correlation were found to exist between shell thickness and body weight, linear morphometry, egg length and shape index, Haugh unit, albumen length and yolk index, shape index, yolk width and yolk index. Significant (P<0.05) and negative correlation exist between albumen width and yolk index, while non-significant (P>0.05) and negative correlation exist between albumen index and shape index, yolk height and shape index, albumen length and Haugh unit, albumen width and shape index, shell thickness and albumen height, albumen length, Haugh unit, yolk index, albumen index. Multiple linear regression of the body weight on linear morphometry in the three genotypes were highly significant (P<0.01) with coefficient of determination of 0.92, 0.88 and 0.36 for Funaab Alpha, Shika Brown and local chicken respectively. This result suggests that evaluation of linear measurements in Funaab Alpha and Shika Brown would appear to be a useful criterion to improve body weight. Two base pair substitution mutation (GT and CA) were found on locus 5 chromosome for the Funaab Alpha and locus 6 chromosome for the Shika Brown and local chicken respectively. Local genotype had highest number (6) of haplotypes while Funaab Alpha and Shika Brown had haplotypes number of 4 each. This suggested that local chicken had more allelic variation than the other two genotypes. On the other hand, Funaab Alpha had heterozygosity of 0.48 more than the Shika Brown and local chicken with heterozygosity of 0.44 each, indicating higher genetic variability. Meanwhile, negative theta value (-0.0843) obtained in F statistics indicated heterozygote excess (outbreeding) which means that the chickens were outbred. Genetic distances and identities revealed that Funaab Alpha and Shika Brown were most related (0.07) with closest identity (0.93) than any other group in this study. Association of cGH gene with linear body measurements and production performances revealed non-significant (P>0.05) differences in most traits between the mutant and the normal genotypes.

Keywords: Chicken growth hormone (cGH) gene, Linear morphometry, Production performance, Funaab Alpha, Shika Brown, Local chicken

TABLE OF CONTENTS

CHAPTER PAGE

Cover page

Title page

Certification i Dedication ii

Acknowledgments iii

Abstract v

Table of contents vii

List of tables xi

List of figures xii

List of appendices xiii

CHAPTER ONE INTRODUCTION

1.1 Background information 1

1.2 Problem statement 5

1.21 Objectives of the study 7

1.24 Justification of study 7

1.25 Scope of the study 9

CHAPTER TWO LITERATURE REVIEW

2.1 Chicken production in Nigeria

2.1.1 The chicken 10

2.1.2 The chicken farmer 12

2.1.3 The structure of Local chicken production 13

2.2 Genetic characteristics of the Local chicken 14

2.3 Production characteristics 17

2.3.1 Free range system 17

2.3.2 Semi-intensive system 17

2.3.3 Egg production 18

2.3.4 Meat and egg production 18

2.3.5 Economic value of the native chicken 19 2.4 Improvement of chicken production in Nigeria 21

2.4.1 Introduction of exotic breeds 21

2.4.2 Crossbreeding of local and exotic breeds 22

2.4.3 Improvements in production environment 24

2.4.3.1 Housing 24

2.4.3.2 Disease control 25

2.4.3.3 Financial empowerment of farmers 27

2.4.3.4 Capacity development of farmers 28

2.4.4 Development of improved local chickens 28

2.5 Characteristics and conservation of chicken genetic resources 29

2.5.1 The Nigerian Chicken Genetic Resources 31

2.6 Shika Brown layer chicken 32

2.6.1 History /Origin 32

2.6.2 Performance of the Shika Brown 33

2.6.3 Present stage of development 35

2.7 Some reported breed development project 36

2.7.1 Funaab Alpha layer chicken 36

2.7.1.1 History/Origin 36

2.7.2 Performance of Funaab Alpha chicken 36

2.7.3 Present stage of development for Funaab Alpha 37

2.8 Linkage of research to industry 37

2.8.1 The Nigeria situation 37

2.8.2 African chicken genetic gain 40

2.9 Layer chicken production 43

2.9.1 Brooding and chick stage 43

2.9.1.1 Growth performance of chicks 45

2.9.1.2 Feed and feed intake in chicks 45

2.9.1.3 Weight gain in chicks 47

2.9.1.4 Feed conversion ratio 47

2.9.1.5 Disease management in chicks production 48

2.9.2 Grower stage of layer production 49

2.9.2.1 Rearing conditions 49

2.9.2.2 Growth performances of grower chicken 50

2.9.2.3 Feeding and feed intake in grower chicken 51

2.9.2.4 Weight gain in grower chicken 52

2.9.2.5 Feed conversion ratio in grower chicken 53

2.9.2.6 Disease management in grower chicken 54

2.9.3 Laying stage 55

2.9.3.1 Point of lay 55

2.9.3.2 Rearing conditions of layer chickens 56

2.9.3.3 Cage systems 57 2.9.3.4 Non cage system 58

2.9.3.5 Nutrition and genetics of laying birds 60 2.9.4 Production performance in layer chicken 61

2.9.4.1 Feeding and feed intake in layer chicken 61

2.9.4.2 Hen day production 63

2.9.4.3 Egg weight 63

2.9.5 Egg quality in layer chicken production 64

2.9.5.1 Egg colour and shape 64 2.9.5.2 Percent shell, albumen and yolk 66

2.9.5.3 Shell quality 66

2.9.5.4 Albumen and yolk indices 67

2.9.5.5 Haugh unit 68

2.10 Phenotypic factors influencing layer strain performance 69

2.10.1 Linear body composition 69

2.10.2 Relationship between linear body composition and growth performance 70

2.10.3 Relationship between linear body composition and laying performance 71

2.11 Genotypic factors influencing growth and laying performance 72

2.11.1 Gene and growth hormone(GH) 72

2.11.2 Chicken growth hormone gene 72

2.11.3 Functions/uses of chicken growth hormone (cGH) gene in chicken research 73

2.12 Chicken growth hormone (cGH) gene isolation 75

2.12.1 Sample collection 75

2.12.2 Steps in characterization 76

2.12.2.1DNA isolation from blood sample for RFLP studies 76

2.13 Sequencing of cGH gene 79

CHAPTER THREE

MATERIALS AND METHODS 80

3.1 Study Area 80

3.2 Study Overview 80

3.3 Experiment 1:

Determination of growth, laying performance and egg quality characteristics

of three chicken genotypes in Nigeria 81

3.3.1 Experimental location 81

3.3.2 Experimental birds 81

3.3.3 Management of experimental birds 81

3.3.4 Experimental diets 82

3.3.5 Experimental design 82

3.3.6 Statistical model 82

3.3.7 Data collection 84

3.3.8 Data analysis 85

3.4 Experiment 2:

Determination of the linear morphometry and their relationship with production

performance of the three chicken genotypes in Nigeria 86

3.4.1 Experimental birds and design 86

3.4.2 Establishment of relationship between growth, egg quality characteristics

and laying performance of the three chicken genotypes in Nigeria 86

3.4.3 Data collection on linear morphometry 86

3.4.4 Data analysis 87

3.5 Experiment 3:

Characterization of chicken growth hormone (cGH) gene and relationships

with production performance and linear morphometry 87

3.5.1 Blood sample collection and processing 87

3.5.2 Experimental design 87

3.5.3 Genomic DNA isolation 88

3.5.4 Chicken growth hormone (cGH) gene primer 89

3.5.5 Polymerase chain reaction (PCR) 89

3.5.6 Agarose gel electrophoresis 89

3.5.7 Data analysis 89

3.5.8 Sequence analysis 89

3.6 Association of chicken growth hormone (cGH) gene with linear morphometry

and production performance 90

CHAPTER FOUR RESULTS AND DISCUSSION

4.1 Experiment 1:

Determination of growth, laying performance and egg quality characteristics of the three chicken genotypes in Nigeria

4.1.1 Growth performance index of the three chicken genotypes in Nigeria during the

chick stage (0 – 8 weeks of age) 94

4.1.2 Growth performance index of the three chicken genotypes in Nigeria during the

grower stage (9 – 20 weeks of age) 96

4.1.3 Laying performance and egg quality characteristics of the three chicken genotypes

in Nigeria at 36th week of egg production 99

4.1.4 Pearson‟s correlation of the egg quality characteristics of the three chicken genotypes in Nigeria 107

4.2 Experiment 2:

Determination of the linear morphometry and their relationship with production performance of the three chicken genotypes in Nigeria

4.2.1 The linear morphometry of the three chicken genotypes in Nigeria during the

chick stage (0 – 8 weeks of age) 108

4.2.2 The linear morphometry of the three chicken genotypes in Nigeria during the

grower stage (9 – 20 weeks of age) 110

4.2.3 Multiple linear regression of the body weight (dependent variable) and linear morphometry (predictors) of the three chicken genotypes in Nigeria 114 4.2.4 Pearson‟s correlation of the body weight, linear morphometry, laying performance

and egg quality characteristics 117

4.3 Experiment 3:

Characterization of chicken growth hormone (cGH) gene and relationships with production performance and linear morphometry

4.3.1 Haplotype and Nucleotide diversity of the cGH gene of three breeds of chicken 125

4.3.2 Variation in G>T and C>A mutations revealed by cGH gene Single Nucleotide

Polymorphisms in three genotypes of Nigerian chicken 128

4.3.3 F-Statistics table of the locus and allele in the three genotype studied. 130

4.3.4 Genetic Distances and Identities in the three genotype of Nigerian chicken as

revealed by cGH gene. 134

4.3.5 The Performance of the GG>GT and CC>CA cGH SNPs on the linear morphometry

of the Shika Brown. 138

4.3.6 The Performance of the GG>GT and CC>CA cGH SNPs on the linear morphometry

of the Local chicken. 141

4.3.7 The Performance of the GG>GT and CC>CA cGH SNPs on the linear morphometry

of the Funaab Alpha. 144

4.3.8 The Performance of the GG>GT and CC>CA cGH SNPs on the egg characteristics

and laying performance of the Shika Brown. 147

4.3.9 The Performance of the GG>GT and CC>CA cGH SNPs on the egg characteristics

and laying performance of the Funnab Alpha chicken. 150

4.3.10 The Performance of the GG>GT and CC>CA cGH SNPs on the egg characteristics

of the Local chicken 153

4.3.11 Mean separation of GG>GT and CC>CA cGH SNPs on the linear morphometry

of the three genotypes 156

4.3.12 Mean separation of GG>GT and CC>CA cGH SNPs on the egg characteristics

and laying performance of the three genotypes 158

CHAPTER FIVE CONCLUSION, RECOMMENDATION AND CONTRIBUTION TO KNOWLEDGE

5.1 Conclusion 160

5.2 Recommendation 162

5.3 Contribution to knowledge 163

REFERENCES 165

CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND INFORMATION

Agriculture is a very important sub-sector of the Nigerian economy, providing food, fibre and foreign exchange to the populace and contributing about 40% of the gross domestic product (GDP) and 70% of employment to the workforce (Asuquo, 2013). The animal production component of the country‟s agricultural production accounts for 5 – 6% of the overall national GDP and 15 – 20% of the total agricultural GDP (Asuquo, 2013). Martin (2001) reported that products from food animals provide more than 33% of the protein consumed in human diets globally and about 16% of food energy consumed. In addition to the provision of protein of high biological value, livestock and poultry are sources of livelihood for millions of people, source of food security and poverty alleviation, source of income and employment and source of foreign exchange.

Specifically, poultry production is considered in terms of its substantial contributions to farmer‟s household economy. This contribution could be measured in terms of direct income benefits which play vital role as source of readily-available cash to rural poultry farmers. In the tropics, chickens particularly, serve as affordable sources of meat and egg on account of their feed efficiency, short life cycle, fast growth rate, and quick return on investment (Oluyemi and Roberts, 2007). Despite the large numbers of the different species of livestock, the average per capita animal protein intake in Nigeria is abysmally low at 10g per day as against the FAO/WHO recommendation of 35g per day. Thus Nigeria remains among the least consumers of animal protein in Africa (Asuquo, 2013), with the average animal protein intake per capita per day in Africa, Eastern Europe, Western Europe and North America being 11, 33, 39 and 66g, respectively. One of the reasons advanced for this low meat consumption level is that the growth rate of the human population is not matched with growth in livestock population (Asuquo, 2013).

Therefore, FMRD (2004) estimated animal protein intake in Nigeria in the year 2000 at 18g/caput/day which is below the recommended minimum level of 35g/caput/day recommended by the FAO. Ademosun (2007) observed that the problem of malnutrition particularly protein malnutrition, was a real one in most developing countries of the world and that these countries were mostly located in the warm humid tropics where the level of animal protein intake represented about one-tenth of the level of intake in some advanced countries.

Adene and Oguntade (2006) observed that the local chicken constitutes 75 to 80% of the total population of chickens in Nigeria, while Nwakpu et al. (1999) reported that native chickens constituted about 80% of the 120 million poultry birds found in Nigeria. These birds are, however, characterized by slow growth, small body and egg size, which may not be desirable in a modern competitive economic situation (Ebangi and Ibe, 1994). These native birds are nevertheless known for their superior adaptation in terms of their resistance to endemic diseases and other harsh environmental conditions compared to the imported exotic birds (Nwakpu et al., 1999). The slow growth of the Nigeria local chicken is largely attributable to genetic limitations. These strains fail to respond to the improvements in environmental conditions such as improved nutrition, housing and health care. The ultimate result is poor growth and egg laying performance leading to low profitability under intensive production conditions.

Udedibie et al. (2000) stated that inadequate supply of animal protein products is not as a result of inadequacy of their number but due to poor productivity, hence the need for improvement and increase in domestic meat production. Ibe (1990) suggested that considering the huge foreign exchange that results from the importation of improved exotic stock, it is desirable to improve the local stock in the environment in which they are fairly well adapted. Thus, animal breeders and geneticists are faced with the challenge of applying genetic tools and methods to bring about efficiency in production. The challenge before the breeders is, therefore, to develop strains with the desired production traits using selection and breeding techniques (Chineke, 1998).

The need to overcome the gene based constraints of the Nigeria local chicken and to improve on its production performance which will results in an increase in the daily protein consumption of an average Nigerian prompted the introduction of the National Rolling Plan (NRP) of 1980 (Omeje et al., 2013). The Rolling Plan of 1980 – 1985 made provisions for the establishment of poultry foundation lines to enable the country produce her own commercial day old chicks. The then Federal Ministry of Science and Technology took responsibility to supervise and sponsor the pilot project hosted by the National Animal Production Research Institute (NAPRI), Ahmadu Bello University, Shika Zaria. The project led to the development of a strain of layer-type chicken known as „Shika Brown‟ as the first ever Nigerian breed of commercial layer-type chicken (Omeje et al., 2013), although the breed has not been test run in all parts of the country.

Genetic improvements of livestock and poultry populations are keys to increasing production of high-quality animal food products in an ethically–responsible manner (NPFAP, 2002). Such a process will mean selecting production traits that are highly and positively correlated and hence producing animals that are capable of high performance.

Generally, the genetic diversity of domestic animal breeds allows farmers to select stock or develop new breeds in response to changes in the environment, threat of disease, new nutritional requirements and societal needs (FAO, 2007). However, the amount of genetic variation detectable in an animal population is related to the magnitude of genetic improvements achievable within the species, hence growth rate is a relevant tool for verifying the growth performance and productivity of livestock. Under such evaluation process, quantitative measures for size and shapes become necessary for estimating genetic parameters (Chineke, 2000) and rapid growth rate becomes an essential criterion for improvement in meat animals as both genetic and environmental factors are known to affect it.

Growth hormone (GH) axis and the transforming growth factor-β sub-family are the most important groups of genes that are involved in a wide variety of physiological functions such as growth and reproduction (Enayati and Rahimimianji, 2009). Chicken growth hormone (cGH) is a polypeptide hormone synthesized in and secreted by the pituitary gland (Thakur et al., 2009). It contains 5 exons and 4 introns with an overall length of 4.1kb (Kansaku et al., 2008). The genes of cGH are highly polymorphic, which involves a wide variety of physiological functions such as growth, body composition, egg production, aging and reproduction (Apa et al., 1994). The chicken growth hormone gene is therefore considered one of the most important candidate genes that can influence chicken performance traits because of its crucial function in growth and

metabolism (Byatt et al., 1993).

First isolated and sequenced by Lamb et al. (1988), polymorphisms in the cGH have been widely studied by restriction fragment length polymorphisms (RFLPs) or sequencing (Yan et al., 2003). The gene encodes a 191-amino acids, mature growth hormone protein and a 25- amino acid signal peptide. The cGH has 4,101 base pairs and consists of five exons and four introns,

differing in this from its mammalian counterpart (Tanaka et al., 1992).

Considerable diversity in the cGH gene exists between native breeds and commercial

breeds such as Avian Parental, Arbor Acre broilers, and Hy-line layers (Ip et al., 2001; Nie et al., 2002). For example, Chinese native chickens are genetically diverse (Zhang et al., 2002) and have distinctive characteristics, including differences in feather colour, growth rate, meat characteristics and reproductive performance. Similarly, the Nigerian locally adapted chicken has been shown to exhibit such distinct characteristics from the exotic ones by the recent studies of Ilori et al. (2016) using insulin-like growth factor gene (IGH -1), a candidate gene for growth, body composition and metabolism, skeletal characteristics and growth of adipose tissue and fat deposition in chickens. Most of the variations in a gene are single nucleotide polymorphisms (SNPs) arising from substitution, deletion or insertion of a single nucleotide. A single SNP can greatly affect performance traits. For example, the sex-linked dwarf allele in chicken is a single nucleotide mutation at an exon-intron junction of the GH receptor gene (Huang et al., 1993). Significant progress has been made in associating quantitative trait loci (QTL) with SNPs in domestic animals (Nie et al., 2005).

The low animal protein consumption in Nigeria highlights the need for improvements in livestock production as a panacea to protein insufficiency in human nutrition. Presently, there are limited molecular studies of candidate genes for economic traits in Nigerian indigenous chickens, especially in south eastern Nigeria and this has necessitated the needs for this study since the chicken growth hormone (cGH) gene could be a genetic locus or linked to a major gene affecting

the growth in the chicken populations (Yan et al., 2003).

1.2 PROBLEM STATEMENT

It is an acknowledged fact that local poultry production contributes to the income and well being of the rural dwellers, generating 19 – 50% of rural family income, constituting about 77% of the national flock and contributing about 98% of poultry products consumed in the villages of developing countries (Sonaiya, 2007). However, the sector suffers set backs as a result of the slow growth rate and small egg size of the local birds, which is not desirable in a competitive economic situation (Ebangi and Ibe, 1994). While several governments in Nigeria have developed policies promoting agriculture as a vehicle for poverty alleviation, food security, employment creation and expansion of the private sector generally, family poultry production has received insufficient attention due to lack of access to the available information and development ideas for this subsystem in a complex farming system (Sonaiya, 2005). Since then, various schemes have been implemented but most had used single genetic improvement approach rather than a combined approach which should include vaccination, feeding, housing improvement and farmers training (Sonaiya, 2005). For example, Elzubeir (1990) reported that distribution of local hatchable eggs were hindered by low hatchability under natural breeding conditions and the difficulty of distributing hatching eggs in rural areas. Similarly, attempts at distribution of day old chicks failed elsewhere due to limitation of breeding stock, hatching and brooding facilities, the high cost of chick production and difficulty in distribution (Musharaf, 1990). Earlier selection of indigenous cocks based on phenotypes had to be abandoned as it did not increase egg production (Elzubeir, 1990).

Again, poultry genetic resources in Nigeria suffered significant losses due to global consolidation of commercial poultry breeding companies, with few of these companies operating with narrow genetic base, resulting in loss of experimental lines, most of which were generated in research institutions due to lack of fund for continuity and retention of lines (Adebambo, 2015). There is, therefore, a growing concern and felt need for the conservation of the local chickens in developing countries such as Nigeria. This is geared towards exploitation of desirable traits of current and future economic importance and of scientific interest in these chickens. Usually, crossbreeding and grading-up programmes depend heavily on introduction of exotic lines and the assembling and adaptation of local strains to improve management conditions. However, the earlier introduction of exotic (Rhode Island Red, (RIR)) cocks into the Nigeria as a systematic chicken upgrading process, through replacement of Nigerian cocks with RIR cocks failed, as the

RIR cocks could not thrive under the poor rural production conditions (Adegbola, 1988). Considering the huge foreign exchange implication of importing such exotic stocks and its associated diseases problems, Ibe (1990) suggested that it may be more desirable to improve the local chickens in the environment to which they are fairly well adapted.

Again, there is a general consensus that continued introduction of high yielding livestock breeds into traditional and extensive production systems could lead to gene erosion in indigenous animals (Sere and Steinfeld, 1996). The loss of some major gene within and between breeds is detrimental not only from the perspective of culture and conservation but also utility since lost genes may be of future economic importance (FAO, 2000b).

1.3 OBJECTIVES OF THE STUDY

The general objective of the study was to determine the influence of chicken growth hormone (cGH) gene on the linear morphometry, growth and laying performances of three chicken breeds in Nigeria raised under experimental conditions.

The specific objectives of this study were:

To determine the growth, laying performance and egg quality characteristics of three breeds of chicken (Funaab Alpha, Shika Brown and Local chicken) reared under experimental conditions in Nigeria. ii. Determine the linear morphometry of the chicken breeds and to establish the relationships between the linear morphometry, growth, laying performance and egg quality characteristics of the chickens.

iii. Characterize the cGH gene status of the three chicken breeds and to establish its relationships with the morphometry and production performances of the chickens.

1.4 JUSTIFICATION OF STUDY

Considering the value of local poultry production to farmers and its contribution to their income, there is no justification for not according very high priority to general improvement of the various strains of locally-adapted chickens in Nigeria.This is specifically because village chicken systems are characteristically indigenous and are integral parts of the farming system, with short life cycles and quick turnovers, based on low input production systems with outputs accessible at both inter-household and intra-household levels and also a means of converting low quality feed into high quality protein. Moreover, land which is a critical production resources is not a limiting factor in village chicken production system. Consequently, disadvantaged groups in the community could be direct beneficiaries of rural chicken improvement programmes (Kitalyi, 1998).

According to Sonaiya (1990a) the intensive and semi-intensive poultry production systems which mushroomed in Nigeria in the 1970s almost collapsed because of grain deficit. As a consequence during the 1980s, there was a substantial increase in the quantity of rural poultry meat in the market chiefly because of the decreasing supply of commercial poultry. However, it is known that households that accept innovation for semi-scavenging poultry production usually increase weekly consumption of eggs and meat. Therefore, several poultry scientists have recently suggested a specific scientific thrust for rural poultry aimed at improving the understanding of the biological and socio-economic factors affecting the input-output relationships and the economic efficiency of the production system (Sonaiya, 2007). According to Horst (1988), the genetic resource base of the indigenous chickens in the tropics is rich and should form the basis for genetic improvement and diversification to produce a breed adapted to the tropics. Furthermore, the improvement of poultry chickens to meet human needs is dependent on variations, both within and between breeds. Such variations among individuals or groups in the breed bring about opportunity for selection and breeding. Thus, the genetic diversity of local chickens breeds and species makes it possible for scientists to select stocks or develop new breeds in response to changes in the environment, threat to disease, new nutritional requirements and societal needs

(FAO, 2007). Therefore, any loss of genetic variation will limit man‟s capacity to respond to changes in economic forces for the exploitation of animal product in tomorrow‟s world. The ultimate strategy is to choose parents with desirable genes, which can be passed on to future generations. Molecular genetic techniques that involve identification of trait genes, DNA sequencing, etc result in more rapid and directional genetic improvement. The application of molecular genetics-based technologies can be viewed as an essential unifying feature of contemporary investigations in animal industry since they could be used to collect more detailed genotypic information on individual as well as information on which alleles or chromosomal segments are transmitted from parents to offspring (Levin et al., 1994). They can also generate datasets of unprecedented size for animal agriculture, such as those resulting from studies of genomic sequence and polymorphisms and from large-scale gene expression analyses using

microarrays.

When compared with other candidate genes in chicken such as growth hormone receptor (GHR), ghrelin, growth hormone secretagogue receptor (GHSR), insuline like growth factor 1 and 2 (IGF 1 and 2), insuline like growth factor binding protein 2 (IGF BP-2), leptin receptor (LEPR), pituitary-specific transcription factor-1 (PIT-1), bone morphogenetic protein receptor type ii (BMPR 2), phosphoenolpyruvate carboxykinase-C (PEPCK-C) gene, the nucleotide diversity (degree of polymorphism within a population) of cGH gene was somewhat higher even in within a similar base populations (Nie et al., 2005). This study compared the linear morphometry and production performance of three genotypes of chicken in Nigeria characterizing the chicken growth hormone (cGH) gene to determine the best performing breed. Specifically, identification of polymorphisms in the chicken growth hormone (cGH) gene were associated with economic traits in the three genotypes. Similar research is ongoing at levels under the African Chicken Genetic Gains (ACGG) projects although characterization of cGH gene is not included in the programme. The outcome of this research will predominantly be evident in commercialization of the best performing genotype.

1.5 Scope of the study:

The study is restricted to the influence of chicken growth hormone (cGH) gene on the linear morphometry and production performance of three chicken breeds in Nigeria namely: the Funnab Alpha chicken, the Shika Brown, and the Local chicken. The study covered a period of ten months and were grouped into three experiments:

Experiment 1: Growth performance and linear morphometry experiments.

Experiment 2: Laying performance and egg quality characteristics.

Experiment 3: Genomic analysis and characterisation of chicken growth hormone (cGH) gene.

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