ABSTRACT
Fifty hens and five cocks from a random mating population of light local chicken ecotype (LLCE) were mated and the fertile eggs hatched to obtain the parent generation (G0) used for this study aimed at improving egg production traits in the LLCE using a selection index. The hens were monitored for short-term (90-days from first day of lay) egg production traits namely: Body Weight at First Egg (BWFE), Average Egg Weight (AEW) and Total Egg Number (TEN). Data obtained were subjected to statistical analysis using SPSS (2001) and paternal half-sib model with Harvey (1990) to estimate descriptive statistics and genetic parameters respectively. These were employed in constructing the selection index. Selection for all the selection criteria (BWFE, AEW and TEN) was in the positive direction. Selected parents were mated to produce next generations – G1 and G2. Selection differentials, selection intensities and genetic response due to selection were also estimated. A control population which spanned for three generations (each generation had its own control population) was used to monitor environmental changes and to estimate the genetic changes due to selection. There were significant increases (P<0.05) in BWFE, AEW, and TEN in the selected populations over the three generations of study such significant increases (P<0.05) were not observed in the control population. Heritability estimates for all traits in all generations and populations were moderate to high. The heritability of the index was also moderate. Such moderate to high heritability estimates indicate high additive genetic variances, implying that these traits were most passed on from the parents to their offspring. Low to high positive genetic and phenotypic correlations was observed between BWFE and AEW in all populations of study. The genetic correlation and phenotypic correlation between BWFE and EN, and between AEW and EN, was moderate to highly negative for all generations and populations of study. A positive genetic correlation was observed between AEW and TEN in G2 of the selected population. A cumulative selection differential of 269.38g, 1.58g and 3.88 eggs were obtained for BWFE, AEW and TEN respectively. Selection response for traits increased over the generations in a fairly linear manner. Realized response per generation was estimated to be 94.22g, 0.84g and 4.85eggs for BWFE, AEW and TEN respectively. It is evident that the simultaneous inclusion of BWFE, AEW, and TEN in a selection index generally improved the performance of selected birds over the generations in the Light Local Chicken Ecotype.
TABLE OF CONTENTS
Title page … … … … … … … … … … i
Certification … … … … … … … … … … ii
Dedication … … … … … … … … … … iii
Acknowledgement … … … … … … … … … iv
Table of contents … … … … … … … … … v-vi
List of Tables … … … … … … … … … … vii
List of Figures … … … … … … … … … … vii
Abstract … … … … … … … … … … ix
CHAPTER ONE
INTRODUCTION … … … … … … … … … 1-4
1.1 Background of Study … … … … … … … 1
1.2 Statement of Problem … … … … … … … 2
1.3 Objectives of the Study … … … … … … … 3
1.4 Justification … … … … … … … … 3
CHAPTER TWO
LITERATURE REVIEW … … … … … … … … 5-16
2.1 Egg Production in Chicken … … … … … … 5
2.1.1 Factors Influencing egg Production … … … … 5
2.2 Principles of Selection… … …. … … … … 5
2.3 Selection for Body Weight and Egg Production Traits in Chicken … 9-13
- Use of Selection Index in Chicken … … … … … 13-14
- Basis for Short-Term Egg selection in Poultry … … … 14
2.6 The Nigerian Local Chicken … … … … … … 14-16
CHAPTER THREE
MATERIALS AND METHOD … … … … … … … 17-25
3.1 Experimental Site … … … … … … … 17
3.2 Experimental Animals … … … … … … 17
3.3 Foundation Stock … … … … … … … 17
3.4 Management of birds … … … … … … … 18
3.5 Maintenance of a control population … … … … … 20
3.6 Data Collection … … … … … … … 20
3.7 Data Analysis … … … … … … … … 20
3.7.1 Evaluating the Performance Characteristics … … … 20
3.7.2 Estimation of Genetic Parameters … … … … 21
3.7.3 Measurement of Selection Applied … … … … 23
3.8 Construction of Selection Index using the Selection Criteria … … 24
CHAPTER FOUR
RESULTS AND DISCUSSION … … … … … … … 27-48
4.0 Results … … … … … … … … … 27-41
4.1 Mean Performance of the Various Egg Production Traits Studied … 27-31
4.1.1 Age at First Egg … … … … … … 27
4.1.2 Body Weight at First Egg … … … … … 27
4.1.3 Weight of First Egg … … … … … … 27
4.1.4 Average Egg Weight … … … … … … 27
4.1.5 Total Egg Number … … … … … … 28
4.2 Estimates of Genetic Parameters of the Selection Criterion Traits … 32-36
4.2.1 Heritability Estimates … … … … … … 32
4.2.2 Phenotypic and Genetic Correlation between Traits … … 35
4.3 Measurement of Selection Applied … … … … … 37-40
4.3.1 Selection Differential, Selection Intensity and Selection Response … 37 4.4 Selection Indexes used for the Selection of LLCE Hens … … 40
4.5 Discussions … … … … … … … … 41-47
4.5.1 Mean Performance of the Various Egg Production Traits Studied 41
4.5.2 Heritability Estimates … … … … … … 43 4.5.3 Phenotypic and Genetic Correlation between Traits … … 46
4.5.4 Measurement of Selection Applied … … … … 46
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS … … … … … 49-51
REFERENCES … … … … … … … … … 52-65
APPENDICES … … … … … … … … … 66-88
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF STUDY
The report of the 4th Food and Agriculture Organization (1973) expert consultation on Animal Genetic Resources presented two important objections concerning the endeavour to improve and conserve the local chicken. The first was as to whether the local strains still possess genes, which are useful to the vastly improved exotic strains given the centuries of genetic screening, which the latter have undergone. The second objection pointed to the fact that the process of further screening of the local chicken will be long, laborious and very expensive. However, the results of recent research using local chicken (Ikeobi and Peters, 1996; Ayorinde et al., 2001; Udeh and Omeje, 2001) indicate that the local chicken is a repository of advantageous genes. Secondly, with molecular genetic techniques, genetic improvement of the local chicken is fast and less expensive. Incidentally, third world countries, which established breeding programmes based on the dilution of indigenous germplasm by extensive crossbreeding programme, suffered failures. Those failed efforts have made livestock breeders aware of the importance of indigenous breeds in overall food production systems – because of their adaptation to the environmental stress of the tropics.
In spite of the large number of livestock and poultry in the nation, the animal protein intake per caput per day still falls below the minimum requirement level recommended by UN/FAO (Ayodele and Ajani, 1999). This has been traced to the low production of animals, which could be due to genetic and/or environmental constraints. The above underscores the need to improve the level of animal protein production in Nigeria. Of greater importance is the improvement of the poultry sector since it has a number of advantages – including short generation interval, and production of large number of offspring, due to its peculiar reproductive traits (Ibe, 2001). Furthermore, poultry meat is generally accepted by all religions and societies.
In many countries the development of agriculture and breeding programmes has resulted in serious changes in poultry breeding stocks during the last decades. The establishment of breeding institutions has led to a pronounced supra-regional propagation of certain chicken breeds due to improvements in performance. As a consequence the local breeds have decreased continuously to the same extent as the preferred high performance breeds have expanded. For instance, it was in a bid to satisfy the need for increased production and profitability in intensive production systems to meet the increase in demand for animal protein by the populace that new high yielding and fast growing poultry breeds were introduced into the existing poultry production systems in Nigeria since the late 1950’s (Obioha, 1992). Incidentally, such introduction has resulted in non-integration of the local breeds considered as ‘low producers’ into large-scale poultry production.
Nigeria has rich chicken genetic resources. A good number of workers have documented the characteristics of the local chicken, in terms of morphological, physiological, behavioral and production attributes. Nwosu (1990) gave a review of these. Ibe (1990a, b) identified some major genes of tropical relevance in Nigerian local chicken populations. Perhaps, the most distinguishing feature for physical characterization at present is the body weight of the local chicken found in the various ecological zones of the country (Olori and Soniaya 1992). Observations have shown that local chicken found within the swampy rainforest and guinea savanna regions are lighter in weight than those found within the highlands and sudan savanna regions (Nwosu, 1979). Such differences in body weight can be used to categorize the local chicken broadly as Light Ecotype – those with lighter weight and Heavy Ecotype – those with heavier weight.
Research data on the local chicken in the past 50 years (Hill, 1954; Oluyemi, 1979; Omeje and Nwosu, 1982; Nwosu, 1987; Udeh and Omeje, 2001) indicate that the Nigerian local chicken has useful genetic attributes that can be harnessed in crossbreeding programmes for the development of egg-type and meat-type chickens. However, there exist limitations to the realization of total heterosis in such crosses with the exotic because – the local chicken is unpedigreed, unselected and unsegregated (Omeje, 1985) hence, unlike the exotics the local chicken cannot be considered a purebred. Furthermore, crossbreds from purebred parents show heterosis to the extent that their gene frequencies differ unlike hybrids from similar lines that manifest total heterosis, (Pirchner, 1983).
In order to incorporate the local chicken as a parent breed to produce strains of chicken that are adaptable to the local environment as well as achieving the much desired goal of making Nigeria self-sufficient in the sourcing of poultry breeding stock and boosting her poultry industry, there is need for selective breeding. The practice of selective breeding among local strains has been found advantageous (El-Issawi, 1975). The concept underlying selective breeding is variation. For within a group of individuals there exist allelic variations that affect the outcomes of quantitative traits such as growth, egg production and egg quality traits.
1.2 STATEMENT OF PROBLEM
Not much study has been done on selection of local chicken for meat or egg production; most of the studies have been on crossbreeding with exotic birds. Oluyemi (1979) after seven generations of mass selection on 12-week body weight of the local chicken concluded that the local chicken is not a potential broiler strain. Although the local chicken has been termed a low producer with regards to egg production (40-80 eggs /bird/year under extensive management system), studies relating to the development of the local chicken as a potential layer have shown appreciable improvement in egg production traits of the birds under improved management system (Hill and Modebe, 1961; Nwosu et al, 1979, Omeje, 1985; Tule, 2005). Nwosu and Omeje (1985) further noted that the local chicken has a genetic potential of producing 128 eggs /bird/year. It should be noted that the results of these studies were from random-bred populations. It is quite possible that the local chicken subjected to selection and improved management can do better. This has prompted the present selection study of the local chicken using a selection index approach.
1.3 OBJECTIVES OF STUDY
The objectives of this study are to:
- Estimate genetic parameters, namely heritability of body weight at first egg, egg number and egg weight, and genetic and phenotypic correlations between these traits in the Light Local Chicken Ecotype (LLCE);
- Develop an appropriate selection index (I) for the selection of LLCE using body weight at first egg, and short-term (90 days from first egg) egg production and egg weight;
- Evaluate and summarize selection applied and response over three generations of selection.
1.4 JUSTIFICATION
Over the last decades, poultry management techniques in Nigeria have improved significantly, with rapidly increasing production. However, due to the high cost of production inputs: such as feed and drugs, and the control of the market by the few livestock contract companies, many individuals and farmers could not compete with the companies and had to give up chicken meat/egg production. For these individual farmers, a streamlined production of local chicken could be an option for alternative income generation and for diversification of the agricultural production base.
Akinwumi (1979) reported that 92% of poultry production in Nigeria was derived from indigenous poultry stock. Similar reports though from Asian survey carried out by Prawirokusmo (1988) stated that about 40% of the egg production and 30% meat production in Indonesia was a contribution made by the local type of chicken. Local chickens may appear to produce less than highly specialized exotic breeds, but they are highly productive in their use of local resources and more sustainable over the long term. Products from local poultry stocks are widely preferred because of pigmentation, taste and leanness (Haitook et al, 2003; Horst, 1988). Local chicken can thrive with limited care and feeding and are often more tolerant or resistant to diseases. They are also better able to cope with drastic changes in food and water supplies as well as harsh, variable and extreme weather and climatic condition. By neglecting to develop locally adapted breeds for higher productivity, an opportunity is being missed to help the developing world feed its people.
Barker (1982) argued that there are large phenotypic and possibly genetic variations existing within the indigenous/local breeds and varieties. He suggested that the application of genetics towards improving these stocks should be undertaken through proper evaluation and documentation of these breeds on a suitable selection procedure designed to provide an optimum genotype to the farmer. This implies that a breeding strategy, which recognizes the introduction and development of pure breeds and selection within local breeds, is beneficial. Ahmed and Hasnath (1983) described the usefulness of such strategy in native Delish chicken. Hence, continuous efforts to develop pure lines for meat and egg production locally may equal or excel in the future the best currently available in the country.
No detailed examination of genetic parameter estimates/variance components for egg production traits in Nigerian local chicken have been reported in literature. Consequently, the little breeding experimental programmes on this bird rely heavily on estimates obtained from exotic populations. For effective genetic improvement, knowledge of genetic parameter estimates of the particular breed or population to be improved is essential. Thus this study is imperative to achieving the genetic improvement of the Nigerian light local chicken ecotype.
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