GENETIC
AND ENVIRONMENTAL FACTORS AFFECTING SHEEP PRODUCTION UNDER DESERT CONDITIONS
Ph.
D. Thesis
Mohamed
H. Fahmy
SUMMARY
This
investigation was mainly directed to evaluate the different crosses obtained by
mating Hungarian Merino and Syrian Awassi to local
Barki sheep raised under desert conditions. The genetic parameters, of Barki
sheep were also estimated. These parameters were heritability estimates and
genetic correlations.
Data
were obtained on 3028 lambs born during five successive years from 1961 to 1966
at
The
traits studied were: birth weight, weaning weight, yearling weight and average
daily gain at different intervals and yearling grease fleece weight.
The
fixed effects studied were, breed group, year of birth, sex, age of dam and
type of birth. All these factors were found to have highly significant effects
on all the seven traits studied except age of dam and type of birth effects on
daily gain from weaning to yearling and the effect of sex on yearling grease
fleece weight. The relative importance of the environmental factors differed in
different traits.
The
first cross resulting from mating Merino and Barki (1/2: M 1/2 B) was the
highest group in almost all the traits studied, followed by the third-cross
(3/8M 5/8 B) and (5/8 M 3/8 B), the second-cross (1/4M 3/4B) and (3/4M X 1/4B)
in descending order. Except for (3/4M 1/4B) group, all the other crosses of
Merino and Barki showed a marked heterosis, as expressed by the superiority of
the cross over the two parental breeds.
Crossing
Awassi and Barki proved to be unsuccessful, lambs of
the resulting groups.(1/2 A 1/2 B) and (1/4B 3/4A) showed negative heterosis
and were markedly interior to all other crosses in almost all the traits.
Merino
lambs showed a markedly poor performance in all the characters studied except
wool production, and proved to be less adapted to desert conditions as compared
to Barki.
Heritability
estimates for the seven characters in Barki sheep were obtained from paternal
half-sib correlation. These estimates were0.22 for birth weight,0.46 for
weaning weight, 0.63 for yearling weight, 0.28 for daily gain from birth to
weaning, 0.42 for daily gain from weaning to yearling, and 0.61 for daily gain
from birth to yearling and for yearling grease fleece weight. The heritability
estimate for birth weight of Merino lambs was 0.33. Two extra estimates of the
heritability of birth weight of Barki were estimated by regression of offspring
on dam and intra-sire regression of offspring on dam. They were 0.17 and 0.16,
respectively.
Genetic
correlations among body weights of Barki sheep were positive and moderately
high. These correlations were 0.57 between and weaning, 0.37 between birth and
yearling and 0.78 between weaning and yearling. Genetic correlations between
body weights and grease fleece weight were all negative. These estimates were
-0.04, -0.01 and -1.60, for the correlation between fleece weight and each of
birth, weaning and yearling weights, respectively.
Ain Shams
University, Faculty of Agriculture, Department of Graduate studies,