ABSTRACT
The study was carried out to determine the genetic change in the Nigerian heavy local chicken
ecotype (NHLCE) through selection for body weight and egg production traits. Progenies (G0
generation) generated from breeding parents randomly selected from the parent stock of the
NHLCE formed the materials for the research. On hatching, the chicks were grouped according
to sire families using colour markers. The chicks were brooded and reared according to standard
management practices. They were fed a starter mash containing 18% crude protein and 2800
Kcal/kgME from 0 – 8 weeks and a growers mash containing 15% crude protein and 2670 Kcal/
kgME from 8 weeks to 20 weeks. At 20 weeks, all pullets were moved into individual laying
cages for short-term (16 weeks) egg production. From then the birds were fed layers mash
containing 16.5% crude protein and 2600Kcal/kgME. Data were collected on body weight, egg
weight and egg number. A control population was maintained for each generation and was used
to measure environmental effects. At the end of the 16 weeks egg production period, hens were
subjected to selection using a multiple trait selection index incorporating body weight at first egg
(BWFE), average egg weight and total egg number. The relative economic weights of the traits
and their heritabilities were used to weight the phenotypic values of each trait in the index. The
index score of each bird became a univariate character, which enabled the hens to be ranked for
purposes of selection. Males were selected based on their individual body weight performances
at 39 weeks of age using mass selection. Selected parents from G0 generation were used to
generate the G1 generation which in turn yielded the parents of the G2 generation. Data on body
weight, BWFE, egg weight and egg number were subjected to statistical analysis to obtain
means, standard error of means and standard deviation using the SPSS 2001 statistical package.
Analysis of variance yielded sire component of variance from which the additive genetic
heritabilities of the traits were calculated. Genetic, phenotypic and environmental correlations
between pairs of traits in the index were estimated. Indicators of selection response, namely,
selection differential, expected, predicted and realized genetic gains were determined for each
trait. There were significant increases (P £ 0.05) in all the traits selected. Body weight
performances (sexes combined) increased across the age periods (0 – 20 weeks) from the starting
mean values in G0 generation to the final values in G2 generation. The body weight at hatch
increased from a mean of 30.30g in G0 generation to 33.48g in G2 generation. Body weights at
4th, 8th, 12th, 16th and 20th week of age also showed similar increases. Body weight of males and
females were similarly significantly improved. Mean body weight of males at 12, 16, 20 and 39
weeks of age were 791.40 ± 8.79g, 932.25 ± 7.83g, 1112.60 ± 11.98g and 1693.75 ± 19.91g,
respectively for G0 generation as against 825.28±7.54g, 1027.83 ± 9.90g, 1156.69 ± 11.74g and
2000.00 ± 31.34g, respectively for G2 generation. For females, body weights at 12, 16 and 20
weeks as well as BWFE were 667.98 ± 6.30g, 791.52 ± 6.24g, 911.59 ± 6.33g and 1330.44 ±
2.141g, respectively in G0 generation. The corresponding values for G2 generation were 673.94 ±
6.48g, 812.54 ± 7.72g, 939.64 ± 7.28g and 1428.48 ± 3.051g, respectively. For egg production,
significant improvements were also made. Total egg number and average egg weight increased
from 75.60 eggs and 41.27g, respectively in G0 generation to 79.38 eggs and 43.18g, respectively
in G2 generation. Selection differential values were positive and high for 39 weeks body weight
in males across the three generations (mean, 302.19g) as well as for total egg number (mean,
10.74eggs) and average egg weight (mean, 0.47g) in females. It was, however, negative on the
average for BWFE (-5.41g). Selection intensity values for mass selection in males were 2.11,
1.75 and 1.16 for G0, G1 and G2 generations, respectively. Mean selection intensity values for
total egg number, average egg weight and body weight at first egg were 0.729, 0.106 and -0.277,
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respectively. For index values, selection differentials (ΔSI) were equally positive across the three
generations and selection intensity (iI) remained relatively stable viz. 0.703, 0.989 and 0.890 for
G0, G1 and G2 generations, respectively. Direct selection responses namely, expected, predicted
and realized genetic gains were mostly positive for all traits selected. Expected average direct
genetic gain per generation for egg number, egg weight and BWFE were 12.58 eggs, 2.98g and
25.04g, respectively. For gain in index traits due to selection on index score, a mean value of
1.705 eggs was obtained for total egg number, 0.949g for average egg weight and 43.93g for
BWFE. The ratio of realized to expected genetic gain were positive across the three generations.
Specifically, a mean ratio of 0.61 was obtained for 39 weeks body weight in males, 1.58 for
BWFE, 1.70 for average egg weight and 1.75 for total egg number, for females. The estimate of
additive genetic heritability (h2) ranged from 0.12 to 0.24 for egg number, 0.34 to 0.43 for egg
weight and 0.57 to 0.70 for body weight. Estimates of genetic correlation (rg) in whole
populations across the three generations ranged from -0.01 to 0.01 for EN-EW, -0.06 to 0.01 for
EN-BWFE, and 0.002 to 0.02 for EW-BWFE. For phenotypic correlation (rp), a range of -0.12
to 0.09, -0.04 to 0.08, and 0.21 to 0.23 were obtained for EN-EW, EN-BWFE, and EW-BWFE,
respectively whereas, for environmental correlation, a range of 0.55 to 1.31, 0.52 to 0.69, and
0.38 to 0.85 were obtained, respectively for the same pairs of traits.
TABLE OF CONTENTS
Title page – – – – – – – – – i
Certification – – – – – – – – – ii
Dedication – – – – – – – – – iii
Acknowledgement – – – – – – – – iv
Abstract – – – – – – – – – vi
Glossary of terms – – – – – – – – viii
Table of content – – – – – – – – – ix
List of table – – – – – – – – – xiii
1.0 INTRODUCTION – – – – – – – 1
1.1 Research objectives – – – – – – – 3
1.2 Problem statement – – – – – – – 4
1.3 Justification – – – – – – – – 5
2.0 LITERATURE REVIEW – – – – – – 6
2.1 Characterization of the Nigerian indigenous chicken – – 6
2.2 Variation among the indigenous chickens – – – – 8
2.3 Egg Production in Chickens – – – – – – 8
2.4 Genetic factors influence egg production – – – – – 9
2.4.1 Age at sexual maturity (ASM) – – – – – 9
2.4.2 Body weight at sexual maturity (BWSM) – – – – 10
2.4.3 Single gene effects – – – – – – – 10
2.4.4 Other genetic components of egg production – – – 11
2.5 Environmental factors influencing egg production – – – – 11
2.5.1 Nutritional factor – – – – – – – 11
2.5.2 Diseases – – – – – – – – 11
2.5.3 Temperature (Heat) – – – – – – – 11
2.5.4 Lighting – – – – – – – – 12
2.6 Genetic improvement in chicken – – – – – 12
2.7 Selection strategies – – – – – – – – 13
2.8 Genetic relationship between traits – – – – – 14
2.9 Economic weights (values) of quantitative traits in farm animals – 15
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2.10 Genetic parameters for body weight, egg number and egg weight
in chickens – – – – – – – – 20
2.10.1 Heritability – – – – – – – – 20
2.10.2 Genetic relationships – – – – – – – 22
2.10.2.1 Relationship between growth and reproduction – – – 22
2.10.2.2 Relationship between egg production and other productive traits – 23
2.11 Effect of selection – – – – – – – 23
2.11.1 Effect of selection on genetic variance and heritability – – 23
2.11.2 Genetic and phenotypic correlations – – – – – 24
2.12 Response to selection (R) – – – – – – 25
3.0 MATERIALS AND METHOD – – – – – 27
3.1 The study site – – – – – – – – 27
3.2 The reference population – – – – – – – 27
3.2.1 The foundation stock or base population – – – – 27
3.2.2 Generation of the starting stock (G0 generation) – – – 28
3.3 Management of the G0 generation – – – – – 28
3.4 Establishment of control population – – – – – 31
3.5 Generation and management of G1 and G2 generations – – – 32
3.6 Measurement of traits – – – – – – – 32
3.6.1 (i) Growth trait – – – – – – – – 32
(ii) Body weight at first egg (BWFE) – – – – – 32
(iii) Final body weight of cocks – – – – – 32
3.6.2 Egg production traits – – – – – – – 32
3.7 Selection in the G0 generation – – – – – – 33
3.7.1 Selection within the male population – – – – – 33
3.7.2 Selection within the female population – – – – 33
3.7.3 Construction of selection index – – – – – 33
3.7.4 Determination of relative economic weights – – – – 35
3.7.4. (i) Body weight – – – – – – – – 35
(ii) Egg number – – – – – – – – 36
(iii) Egg weight – – – – – – – – 36
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3.7.5 Selection in subsequent generations (G1 and G2) – – – 37
3.8 Data analysis – – – – – – – – 37
3.8.1 Performance statistics – – – – – – – 37
3.8.2 Estimation of genetic parameters – – – – – 37
3.8.2.1 Heritability (h2) – – – – – – – 38
3.8.2.2 Genetic correlation (rg) – – – – – – 38
3.8.2.3 Phenotypic correlation (rp) – – – – – – 39
3.8.2.4 Environmental correlation (rE) – – – – – 40
3.8.3 Measurement of selection applied – – – – – 40
3.8.3.1 Selection differential (Δs) – – – – – – 40
3.8.3.2 Selection intensity (i) – – – – – – – 40
3.8.3.3 Cumulative selection differential – – – – – 41
3.8.4 Measurement of response to selection – – – – – 41
3.8.4.1 Expected direct response (Ri) – – – – – – 41
3.8.4.2 Cumulative direct response (cumR) – – – – – 42
3.8.4.3 Average direct genetic response per generation – – – 42
3.8.4.4 Expected direct genetic gain per year – – – – – 42
3.8.4.5 Predicted direct genetic response (Rp) – – – – 43
3.8.4.6 Realized (observed) genetic response (ΔGR) – – – – 43
3.8.4.7 Expected genetic gain (response) in the index value due to selection
on the index score (I) – – – – – – – 44
3.8.4.8 Expected genetic gain in the component traits of the index due to
selection on index score (I) – – – – – – – 44
3.8.4.9 Effectiveness of selection – – – – – – 44
4.0 RESULTS AND DISCUSSION – – – – – 45
4.1 Body weight – – – – – – – – 45
4.2 Heritability estimates for body weight at various age periods – – 54
4.3 Selection differentials, phenotypic standard deviation ( ) p s and selection
intensity for males – – – – – – – 59
4.4 Response to selection in the male population – – – – 62
4.5 Total egg number, average egg weight and body weight at first egg – 65
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4.6 Response to selection in the Female population – – – – 69
4.7 Genetic, phenotypic and environmental correlations (rg, rp, and rE) – 72
4.8 Estimates of additive genetic heritability ( 2 )
s h for egg number, egg weight and
body weight at first egg – – – – – – – 75
4.9 Relative economic weight for egg number, egg weight and body weight
at first egg – – – – – – – – – 77
4.10 Selection response in egg number, egg weight and body weight at first egg 79
4.11 Mean values, selection differential, phenotypic standard deviation,
selection intensity, heritability and expected response for index score – 83
4.12 Response in the component traits of the index due to selection on index
score – – – – – – – – – 85
5.0 CONCLUSION AND RECOMMENDATION – – 87
5.1 Conclusion – – – – – – – – 87
5.2 Recommendations – – – – – – – 88
REFERENCES – – – – – – – – 89
APPENDICES – – – – – – – –
CHAPTER ONE
1.0 INTRODUCTION
The report of the FAO expert consultation on animal genetic resources (FAO 1973)
recommended the improvement and conservation of animal genetic resources indigenous to
countries. However, two major constraints delayed its implementation until the 1980s. These
constraints include the lack of funds on the one hand, and the delay caused by the disagreement
between scientists concerning the genetic merits of these indigenous breeds on the other hand.
Most scientists were at this time locked in the paradigm of economic progress as the only value.
Consequently, the prevailing animal production policy then (1960s and 1970s) was to try
to improve tropical breeds by introducing temperate breeds with high genetic merits (AGRI,
2002). Indigenous breeds were considered obsolete. Improving and conserving indigenous
breeds were regarded as uneconomic and, therefore, should be allowed to disappear. But Payne
and Hodges (1997) had noted that the philosophy of improving animal production in the tropics
with temperate breeds did not only fail but also damaged indigenous breed resources.
Humanity shapes biodiversity, knowingly or unknowingly. This biodiversity results both
from natural selection for adaptation and artificial selection through human choices for use
and/or aesthetic value. The preferential selection of distinct genetic traits is reflected in the breed
types and races that are adapted to specific uses or environments. Nigeria is blessed with a vast
array of animal biodiversity (Nwosu, 1990). This array of breeds is a human heritage worthy of
improvement and conservation. Their loss is bound to deplete the quality of human life (Hodges,
2002).
The population of Nigeria was estimated to be about 144 million people (National
Population Commission, 2006). With an estimated population growth rate of 2.9% per annum,
the population is currently about 160 million. The provision of adequate food for this teaming
population is the mandate of the agricultural sector.
Animal agriculture must also provide the animal protein needs of Nigerians. This is an
enormous responsibility. The British Medical Association recommends a minimum animal
protein intake of 34g per caput per day (Okuneye, 2002). Also, the food and Agriculture
Organization (FAO) of the United Nations (1989), recommends 20g of animal protein per caput
per day as the minimum for consumption for developing countries (Okuneye and Banwo, 1990)
but 75g as the optimum for normal growth and development (Food and Agriculture
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Organization, FAO, 1992). This translates to a minimum demand of about 3.4 million
kiogrammes and a maximum of 7.5 million kilogrammes of animal protein per day for a
population of about a 100 million people. But according to Oluyemi (1979), the average animal
protein intake per caput per day in Nigeria was a mere 7.6g or 38% of the FAO minimum
recommendation for developing countries and a mere 10% of the requirement for excellent
growth and development. The Central Bank of Nigeria, CBN (2000) while analyzing the
economic sub-sectors noted that the Gross Domestic Product (GDP) has been on a downward
trend. And since the nature of GDP reflects the standard of living of the citizens it means that the
standard of living of Nigerians has been on the decline. By extension this also implies that the
animal protein intake of the average Nigerian has continued to fall far below the recommended
levels.
The Federal Ministry of agriculture and Rural Development (FMARD)(2008) gave the
estimated number of indigenous chicken in Nigeria as 166 million. The exotic breeds were
believed to number about 5 million. Akinwumi et al. (1979) gave an estimate of about 123.0
million for indigenous fowls and 9.6 million for exotic birds. In addition to the above are
thousands of horses, camels and pigs as well as millions of donkeys, cattle, goats and sheep.
The above statistics are impressive but where are the products? In 1998, out of a total of
101 million metric tones of poultry meat projected for production, only 77 million metric tones
were realized. In 1999, 109 million metric tones were projected but only 82 million metric tones
were supplied by the poultry sector. The figure for the year 2000 was similar as only 88 million
metric tones were supplied out of a total projection of 116 million metric tones (CBN, 2002).
Livestock value is not measured in numbers but in terms of amount of useable animal
products harvested for human consumption (Nwosu,1990). A reliable yardstick for measuring
productivity of animal products is hence the total production and the production per person per
year. Thus, it is significant to note that in 1994, 1996, and 2000 the total meat products (of
various types) produced per person in Nigeria was 8.224kg, 8.694kg, and 8.772kg, respectively
(Okuneye,2002). These figures reveal serious shortages from the recommended 75g per caput
daily animal protein intake or its equivalent 25.375kg per person per annum intake (FAO,1989).
To make up for these shortages, Nigeria must import animal milk and meat products from
other countries. Thus in spite of the enormous number of indigenous livestock resources, Nigeria
remains a net importer of livestock products since the 1980s (Okuneye, 2002). Von Mason
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(1989) stated that Nigeria was the biggest importer of dairy products in West Africa. The 2,428
metric tones of beef and 198,000 metric tones of milk imported by Nigeria in 1987 cost the
nation a whopping sum of US$3.27 million and US$69.00 million, respectively (ILCA, 1991).
This trend has not abated till date (Okuneye, 2002). To bridge the animal protein demand and
supply gap the Nigerian government in the 1970s and 1980s attempted to improve local breeds
of cattle by importing temperate breeds. These efforts failed principally because the exotic
breeds could not adapt to the tropical Nigerian environment as the challenges of tropical climate,
pests and diseases were unbearable to them. The problem of streptothricosis in crossbred cattle
was quite devastating. The importation and rearing of exotic poultry species have not also been
able to bridge this gap. The reasons also include the challenges of stressful environment and
diseases which reduce performance added to the high cost of inputs (genetic and feed materials,
drugs and bio-organics) which discourage so many investors from investing in the industry.
Locally adapted breeds (indigenous species) are better able to survive and produce
valuable products in low input and variable environments (AGRI, 2002). A strategy to develop
these breeds is, therefore, likely to be more sustainable over the long term than reliance on
external genetic resources. Nwosu (1979) had deplored the lack of a co-ordinated effort to
preserve, harness, and improve the genetic potentials of Nigeria’s indigenous livestock breeds.
1.1 Research Objectives
The general objective of this study is to improve the performance of the Nigerian heavy
ecotype local chickens with respect to their body weight and egg production (egg number and
egg weight).
The specific objectives are to:
1. Evaluate the Nigerian Heavy Local Chicken Ecotype (NHLCE) for growth (body weight)
from 0 – 20 weeks of age and for short term (16 weeks) egg production.
2. Estimate the genetic parameters, namely heritabilities (h2) and genetic correlations (rg) as
well as phenotypic and environmental correlations (rp and rE, respectively) of body
weight, egg weight and short-term egg production (egg number) in this population in the
Nsukka environment.
3. Estimate the relative economic weight of egg number, egg weight and body weight at
first egg in the NHLCE.
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4. Undertake selection in the NHLCE using mass selection for body weight in males and a
selection index for body weight, egg weight and short–term egg production (egg number)
in females with a view to improving its performance.
1.2 Problem Statement
There has been a total neglect of the indigenous species of livestock. The raw materials
have remained undeveloped. The few poultry farms and hatcheries in the country are stock
multipliers rather than primary breeders. They depend on foreign sources for hatchable eggs,
commercial day-old chicks, and grand parent stocks, hence the high cost of these inputs and the
low returns of commercial poultry ventures.
The neglect of the local breeds is mostly due to poor product yield resulting from non
improvement as well as from poor and stressful environment. The local chicken for instance is
unattractive to investors because of its small body size (hence poor carcass yield) as well as poor
egg production performance both in total number of eggs laid and the sizes of eggs produced
(mostly pee wees).
It is, therefore, imperative that efforts be channeled towards the improvement of the
Nigerian indigenous chickens. Improvement in body weight performance will increase its carcass
yield and enhance its acceptance as a meat bird while improvement in her egg production
performance (egg number and egg weight) will enhance its acceptance as a source of commercial
egg production. A scientific proof that the local chicken responds positively to genetic
improvement strategies could stimulate public/private sector investment to improve the local
chicken. In this way the value of the native chicken can be enhanced to provide a buffer against
the recurrent shortages and prohibitive cost of animal protein materials in Nigeria.
1.3 Justification
Nigeria is endowed with numerous livestock species which are indigenous to her. These
animals have lived, adapted and produced for centuries in the Nigerian environment (Nwosu,
1990). They, therefore, constitute genetic resources and raw materials capable of being
developed into modern improved breeds and strains. The application of basic principles of
animal breeding and genetics, as well as, improved management practices could significantly
enhance the productive performance of the Nigerian indigenous species of livestock including
the local chicken.
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The improvement of the indigenous livestock resources hence requires a more
methodical, sustained and painstaking approach. Selection provides the basic tool. Selection and
purposeful mating, therefore, are the foundations of a serious effort towards the improvement of
the local chicken. In this era of harsh economic conditions and dwindling national resources,
sustainability becomes the watch word of every endevour. A poultry industry built on imported
inputs (fertile eggs, F1 day – old chicks, feed raw materials, bio-organics, drugs etc) cannot be
sustained. Improving the indigenous stock hence remains the only way of building a strong and
viable poultry industry (Nwosu, 1990, Ikeme, 1990).
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