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, respectively.
For index values, selection differentials (∆SI) 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.
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
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
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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