الفهرس 
General IntroductionOnly 14 pages are availabe for public view
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Abstract
In conclusion, this study indicated that birth weight had high association with preweaning gain and weaning weight than with postweaning gain and final feedlot weight. Therefore, birth weight was a useful predictor for growth rate to weaning, although, breed group clearly influenced this relationship. Moreover, there was a positive response of dam’s milk production with preweaning growth performance.
Results of this study indicated that, in general, final feedlot weight, scrotal size and testicular development could be predicted fairly accurately from pre and post-weaning gain indices using their inclusion of the linear relationships, regardless of the level of energy in feedlot diet and breed group effects. Birth weight was least useful predictor of final weight and scrotal circumference. Preweaning daily gain exert maximum association with hip height, however, the regression lines of hip height on preweaning gain differed significantly between the two breed groups used in this study.
Final feedlot weight had high and almost similar power explaining the variations in scrotal circumference and hip height. Nevertheless, it is obvious that these relationships under effects of the level of energy and the breed group are confounded.
Results of this study indicated that period on test had a significant quadratic effect on scrotal circumference in young bulls. Not only the weight but also hip height was influenced significantly by period on test. Change of body weight on period on test differed significantly between the two levels of energy.
Dietary energy level had a considerable effect on production efficiency, with low ~~ energy level reducing growth rate, feed conversion efficiency, testicular growth and hip height change in feedlot, but giving leaner carcasses compared to the high energy level. The high energy diet produced heavier carcass weight, higher dressing percentage and larger rib eye area compared to the low energy diet. On the other hand, the DSX bulls had similar growth rate and testicular growth, but were significantly taller and resulted in lighter carcass weight, lower dressing percentage and produced similar carcass lean meat