GENETIC AND ENVIRONMENTAL FACTORS AFFECTING SHEEP PRODUCTION UNDER DESERT CONDITIONS
Ph. D. Thesis
Mohamed H. Fahmy
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.
were obtained on 3028 lambs born during five successive years from 1961 to 1966
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.
University, Faculty of Agriculture, Department of Graduate studies,