ESTIMATION OF GENETIC PARAMETERS USING DIFFERENT METHODS IN RHODE ISLAND CHICKENS SELECTED FOR PART- PERIOD EGG PRODUCTION
ESTIMATION OF GENETIC PARAMETERS USING DIFFERENT METHODS IN RHODE ISLAND CHICKENS SELECTED FOR PART- PERIOD EGG PRODUCTION
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Date
2004-05
Authors
NWAGU, BARTHOLOMEW IFEANYI
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Abstract
Data from 4,336 pullets, progeny of 144 sires and 779 dams for strain A and
4,843 pullets, progeny of 158 sires and 1108 dams for strain B belonging to six
generations under selection for part- period egg production to 280 days of age were used
for this study. The data were used to compare heritability (h2) estimates from daughterdam
regression method, with those estimated by variance component estimate method
from five procedures (Harvey method, TYPE 1, MIVQUE, ML and REML of SAS).
Response to selection, genetic and non-genetic correlations among egg production traits
in the two strains were investigated. Effective number of parents and co-efficient of
inbreeding were also calculated for both lines. The chickens were grouped into selected
and control populations within the male and female lines.
The estimates of genetic parameters over the years were obtained after correcting
the data for hatch and year effect. The traits considered in the computation of response to
selection and genetic parameters were egg number (EGG280D), age at sexual maturity
(ASM), average egg weight (EWTAV) and body weight at 40 weeks of age (BWT40).
The heritability estimates from different variance component methods were close
to one another in magnitude and in agreement with those found in literature. The
heritability estimates obtained from variance components (half-sib) were 0.18, 0.15, 0.24
and 0.16 for age at sexual maturity (ASM), egg number (EGG280D), egg weight average
(EWTAV) and body weight at 40weeks of age (BWT40), respectively, for the male line.
The corresponding values for the female line were 0.20, 0.16, 0.29 and 0.21. The
estimates obtained from daughter – dam regression for ASM, EGG 280D, EWTAV and
BWT40 were 0.19, 0.05, 0.28, and 0.27, respectively, for the male line and 0.19, 0.25,
0.27 and 0.20, respectively, for the female line. The standard errors associated with the
parameter estimates were very low which is an indication of their reliability.
Direct genetic response to selection was higher in the female than male line (3.4
vs 0.42 eggs per generation). Selection is therefore much more effective in improving
part year egg production in the female line as compared to the male line. The genetic
correlation estimates between the different economic traits over five generations ranged
from – 0.70 + 0.38 to 0.82 + 0.42 vs – 0.71 + 0.47 to 0.76 + 0.29 for the male and female
lines respectively. The correlation between egg number and egg weight was small and not
significantly different. Age at sexual maturity was highly and negatively correlated with
egg production to 280days in both lines, being higher than – 0.60 in most cases. However
the genetic correlation between egg number and matured body weight (BWT40) showed
no definite trend in the male and female lines.
In the female line, the correlated response in age at sexual maturity as a result of
direct selection for egg production to 280days had negative value. This is also true for
body weight due to selection for increased egg number to 280days. There was a reduction
of 0.89g per year in egg weight due to selection for increased number. In the male line
however except for body weight at 40 weeks, which showed a positive correlated
response of 3.4g per year, all other traits considered showed negative correlated
responses to selection for egg number to 280days of age.
The average inbreeding co-efficient due to finite population for both male and
female populations were equal with a value of 0.005 while values for the control
population were 0.008 vs 0.007 for the male and female line, respectively. The effective
number of parents in each generation averaged 174 vs 187 for male and female lines,
respectively.
It was observed that there was an increasing trend in the co-efficient of inbreeding
per generation over the period of study. Although inbreeding could be adjudged mild in
the study population, there is need to widen the genetic base of the population to avoid
intense inbreeding that could result in selection plateau in due course.
The use of the various estimation procedures or options in this study revealed that
generally the maximum likelihood estimators of SAS are more appropriate in dealing
with Animal breeding data as they are capable of dealing with both random and fixed
effects in a mixed model and are able to handle unbalanced data characteristics of Animal
breeding data. However, if Harvey’s method is to be used for analysis, data set with
missing cells should be edited out before analysis to obtain meaningful estimates.
Daughter – dam regression is recommended in the estimation of heritability due to the
fact that random sampling errors associated with estimates are minimized. The offspring
– parent method excludes the effects of environment more efficiently than those based on
half or full – sibs.
Description
A THESIS SUBMITTED TO THE POST GRADUATE SCHOOL
AHMADU BELLO UNIVERSITY
IN PARTIAL FULFILMENT FOR THE AWARD OF DOCTOR OF
PHILOSOPHY (PhD) IN ANIMAL SCIENCE (GENETICS AND ANIMAL
BREEDING)
DEPARTMENT OF ANIMAL SCIENCE
FACULTY OF AGRICULTURE
AHMADU BELLO UNIVERSITY
ZARIA
Keywords
ESTIMATION,, F GENETIC,, PARAMETERS,, DIFFERENT,, METHODS,, RHODE ISLAND,, CHICKENS,, SELECTED, SELECTED,, PART- PERIOD,, EGG PRODUCTION.