الفهرس 
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Abstract
Abstract
The current work aimed to enhance productivity of local breeds of poultry by studying the effect of crossing between endogenous breeds and foreign breed of chicken on productive traits of cross lines. A cross breeding was conducted between two endogenous breeds Gimmizah (G) and Bandara (B) and one foreign breed Ross 308 (R). A total of 180 parent pure breeds (Gimmizah, Bandara and Ross), and their crossbred lines R ×G, R×B, and G×R chicks beside the control groups of pure chicks (G×G, B×B, and R×R) were evaluated. Body weight, weight gain, feed intake and feed conversion ratio of each genetic group were estimated from the hatching day till 7th week of age. Phenotypic traits including shank length, sternum length and chest girth were measured at the age of 7th week. mRNA Expression of IGF-I and IGF-II genes at two different ages (3 and 7 weeks) were analyzed. The breast muscle and pituitary gland were the chosen tissues for RNA analysis. The results revealed that the R×R chicks displayed significantly higher final body weight, average daily weight gain, and average daily feed intake when compared to the G×G, B×B, and other crossbred chick lines. While both R×B and G×R crossbred chicks had significantly higher final body weights and average daily weight gains than R×G crossbred chicks and local chicks (G×G and B×B). A better feed conversion ratio was observed in G×R, B×B, R×R and R×B chicks. Crossbred lines (R×B and G×R) had higher dressing percentages than R×G and local breeds. The highest muscular expression of the IGF-II gene was recorded in R×G chicks, while the other crossbred lines, R×B and G×R expressed higher levels of the IGF-II gene than purebred lines. In relation to IGF-I, R×B chicks had higher relative expression of this gene than other crossbred and purebred lines. When compared to other crossbred lines (R×B and G×R), the expression of IGF-I in brain tissues was significantly higher in the R×G crossbred line. IGF-II and IGF-I expression levels in brain tissue were higher in the R×G chicks compared to the G×R, G×G, B×B, and R×R chicks. It was concluded that crossing pure Gimmizah or Bandara, as local breeds, with pure Ross 308, as a foreign breed, improved growth traits in the obtained crossbred chicks.
Key words: Gimmizah, Bandara, Ross, Growth performance, IGF genes expression