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.
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:
1.
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);
2.
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;
3.
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....
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Item Type: Postgraduate Material | Attribute: 99 pages | Chapters: 1-5
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