Ayoub, H

Magraby, M

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H Ayoub

M Magraby

Springer

Heritability of the differences in body weight between sexes at different ages in two strains of chickens

Magraby M

Ayoub H

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Genetics Selection Evolution

H. AYOUB

M. MAGRABY

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HERITABILITY OF THE DIFFERENCES  IN BODY WEIGHT BETWEEN SEXES  AT DIFFERENT AGES IN TWO STRAINS  OF CHICKENS

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HERITABILITY OF THE DIFFERENCES
IN BODY WEIGHT BETWEEN SEXES
AT DIFFERENT AGES IN TWO STRAINS
OF CHICKENS
H. AYOUB M. MAGRABY
Faculty of Agriculture,
Ein Shams University
Cairo (Egypt)
* Animal Production Department,
Ministry of Agriculture,
Cairo (Egypt)
SUMMARY
The aim of this investigation was to study the genetic parameters of sexual dimorphism
for body weight at 4, 6 and 8 weeks of age for two strains : Dokki 4 and White Plyn:outh Rock.
The estimates of heritabilities of sex differences in body weight from sire component of
variance at different ages ranged from - 0.20 to 0.6. These estimates suggest a very low magni-
tude of the inheritance of this trait and confirm that selection for sexual dimorphism through
the sires is not expected to be effective.
INTRODUCTION
’ 
In advanced poultry industry, sexual-dimorphism received great attention
during the last 8 years, since broiler production requires uniformity in body weight
at market age. Regarding the fact, that males reach the suitable weight before
females, due to sex-difference, a commonly occurring phenomenon in avian species,
the degree of divergence between sexes has its economic importance.
The published heritability of the difference in weight between males and females
ranged from -130 to 0.36 : BUVANEDR (ig6g), F,IS!N and LEGATES (1966),
YOSHIDAand COLLINS (I967), AYOUB and MERAT (I972). The aim of this paper was
to investigate the genetic parameters of sexual dimorphism for body weight at
4, 6 and 8 weeks of age for the strains, Dokki 4 and White Plymouth Rock.
MAT!RIAI, AND METHODS
Two breeds of chickens were used. The first was Dokki 4, developed by back-crossing,
Barred Plymouth Rock to Fayoumi for 4generations and kept selfmaintained since 1958 at
Dokki experimental farm. The second was White Plymouth Rock which was imported from Holland
about 20 years ago and was selfmaintained since at the same farm. 80 pullets from each breed
were single sire mated in 8 groups, each of 10 dams and i sire. 855 pedigreed chickens of the
two breeds were obtained, of which 323 were Dokki 4 and 532 were Plymouth Rock. Chickens
were weighed to the nearest gm at 4, 6 and 8 weeks of age. Only dams having at least two progeny
of each sex were used and equal numbers of progeny of each dam were recorded for analysis.
Observation on each dam family was taken as the difference between the mean of the two sexes
(T. - if) . The form of the analysis of variance and expected mean squares (EMS) are the same
as given by KINNEY and SIIOFFNER(1965) and as used in the paper by AYOUB and MARAT (i9!2).
Heritability of the difference between sexes was calculated using the following formula.
where 0-: = variance due to differences between sires,
aa = variance due to differences between dams,
o-!Q = variance due to differences between full-sibs.
Some explanation is due to illustrate the estimation of h!1-z), since there is no direct estimate
for 0-;;’(1Z) and a§<1-!>. EISEN and LEGATES (1966) ; BUVANENDRAN (ig6g), explained this point
as follows :
Thus a§e was obtained by substituting the values of aw obtained for males and females in
hierarchical analysis of variance on an individual basis (between and within full-sib families),
according to KEMPTHORNE (1957). Assuming the expectation of COV(,.2) as Zero ad is then
obtained by substitution.
RESULTS AND DISCUSSION
Mean body weight
The average weights and variances of males and females for the two breeds,
given in table i, show that the difference between the two sexes increases with
advancing age, and the variances from male data are greater than those from females
in general. These results hold true with many available references.
Heritability estimates of sex differences in body weight
The results presented in table 2 give h estimates ranging from -0.2o to 0.6 ;
these estimates suggest a very low magnitude of the inheritance of this trait. The
negative values of h’(1-2) were found in 4 cases out of 6. A similar negative estimate
was obtained by AYOUB and MPRAT(1972), at 8 weeks of age (-r.3o), using the
strain « Jouy o. They stated that this negative value was due to the sampling error
generally associated with such estimates based on limited sire numbers, the estimates
of negative values in this case corresponding to a very weak variation between sire
families.

The estimates of h2 of the body weight differences obtained from literature
were generally low, e.g. EISEN and LEGATES (r966), working on Mice found estimates
of h!1_a! as o.oio, o.o84 and o.i¢2, for three, six and eight weeks weights respecti-
vely. YOSHIDA and COLLINS (1967), reported a heritability estimate of o.og for sex
differences in quails at 4 weeks of age ; they also stated that after their selection
experiment, the sex difference in body weight in selected lines remained unchanged.
Findings from the present investigation confirm other findings in the literature,
that selection for sexual dimorphism through the sires is not expected to be effective.
Reçu pour publiccation en septernbre 1975.
ACKNOWLEDGEMENT
The authors wish to express their deep thanks and gratitude to Dr. M. KHIR EL Dm, under-
Secretary of State-Ministry of Agriculture for his encouragement during the course of this work.
Thanks are also due to Dr. A. MOSTAGEER, Faculty of Agriculture Cairo University and
Dr. S. GALAL, Faculty of Agriculture Ein Shams University for their advice and useful criticism.
RÉSUMÉ
HÉRITABILITÉ DES DIFFÉRENCES DU POIDS CORPOREL ENTRE SEXES
A DIFFÉRENTS AGES DANS DEUX SOUCHES DE VOLAILLES
Le but de cette recherche était d’étudier les paramètres génétiques du dimorphisme sexuel
du poids corporel à 4, 6 et 8 semaines d’âge pour les deux souches : Dokki 4 et Phlynzoitth Rock
blaneFae.
Les estimations d’héritabilité des différences entre sexes pour le poids corporel basées sur
la composante « père » de la variance aux différents âges allaient de -o,20 à 0,6. Ces estimations
suggèrent un très faible ordre de grandeur de l’héritabilité de ce caractère et laissent prévoir
un manque d’efficacité de la sélection pour le dimorphisme sexuel basée sur le père.
REFERENCES
AYOUB H., MÉRAT P., 1972. Differences entre families pour le dimorphisme sexuel du poids a un
Age donné chez la Poule. Ann. Ginit. Sgi. anim., 4, 45-9.
BuvnNxrrnxn:v V., 1969. The heritability and genetic correlations of sexual dimorphism for 10 week
weight in poultry. Br. Poult. Sci., 10, 321-5.
EzsErr E. J., LEGATTES J. E., 1966. Genotype, Sex, interaction and the genetic correlation between
the sexes for body weight in Mus Musculus. Genetics, 54, 611-623.
KEMPTHORNE 0., 1957. An introduction to genetic statistics. John Willey and Sons, Inc., New York.
KmNEm T. B. J., SxoaarrEx R. N., 1965. Heritability estimates and genetic correlations among
several traits in a meat type poultry population. Poult. Sci., 44, 1020-32.
YOSHIDA S., COLLINS W. M., 1967. Individual Selection for 4weeks body weight in Japanese quail
in relation to sex dimorphism. Poult. Sci., 46, 1341 (abstr.).


Crossref

An introduction to genetic statistics.

Differences entre families pour le dimorphisme sexuel du poids a un Age donné chez la Poule.

Heritability estimates and genetic correlations among several traits in a meat type poultry population.

Individual Selection for 4 weeks body weight in Japanese quail in relation to sex dimorphism.

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Heritability of the differences in body weight between sexes at different ages in two strains of chickens

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