中文摘要：

选用北京油鸡、隐性白鸡及杂交鸡（北京油鸡♂×隐性白鸡♀）为试验材料，相同条件下饲养14周，自出生起每2周采集1次腿肌和胸肌的肌肉样本，做常规石蜡切片，测定肌纤维的直径和密度。结果表明：随着鸡的生长，肌纤维直径越来越粗，密度越来越小，直径和密度负相关极显著（P〈0．0001）；并且不同品种肌纤维的生长速度差异较大。14周龄时，北京油鸡的腿肌肌纤维直径为42．89μm，杂交鸡是49．29μm，隐性白鸡的达56．93μm；而14周龄的腿肌肌纤维密度，北京油鸡达581．80根／mm^2，杂交鸡是447．53根／mm^2，隐性白鸡为349．87根／mm^2；4周龄到14周龄，北京油鸡和隐性白鸡肌纤维直径差异极显著（P〈0．01）。同一周龄同一品种的鸡，腿肌肌纤维直径大于胸肌，密度则小于胸肌；6周龄的隐性白鸡，腿肌和胸肌肌纤维直径分别是27．96μm和24．61μm，密度分别是1557．50根／mm^2和1809．30根／mm^2。在杂种优势率上，肌纤维直径和密度没有随周龄而呈现递增或递减的规律性变化，且波动比较大；总体来看，杂交后代没表现出杂种优势，而偏向其隐性白鸡母本，表现出一定的母体效应。

英文摘要：

Beijing Fatty, Recessive White Plymouth Rock （RWPR） and a cross between Beijing Fatty（♂） and RWPR （♀） were fed to 14 weeks to investigate the development character of growth of muscle fiber by paraffin slice protocol. The results showed that the diameter of muscle fiber increased with age, while the muscle fiber density decreased. Moreover, the relationship of diameter and density was significantly negative（P〈0. 000 1）. The growth rate of muscle fiber varied among different breeds. The diameter of thigh muscle fibre in Beijing Fatty, cross and RWPR at 14 weeks was 42.89μm, 49.29μm and 56.93μm respectively; Contrarily, the density at 14 weeks was 581.80 piece/mm^2 , 447.53 piece/mm^2 and 349.87 piece/mm^2 respectively; From 4 weeks to 14 weeks , the diameters of muscle fibre between Beijing Fatty and RWPR were significantly different（P〈0.01）. To conclude, the diameter of thigh muscle fibre was greater than that of breast muscle, while the density was smaller; The diameter of thigh and breast muscle fibre in RWPR at 6 weeks was 27.96μm and 24.61μm, and their density was 1 557.50 piece/mm^2 and 1 809.30 piece/mm^2. The heterosis rate of the diameter and density of muscle fibre did not vary steadily along with weeks. As a whole, there was hardly any heterosis in these traits in the offspring from the cross of Beijing Fatty （♂） and RWPR （♀）, however, they tended to follow that of the maternal line.