Animal selection based on growth rate has received greater attention as a selection index. While many have evaluated the effect of growth rate on muscle characteristics and meat quality, few studies have attempted to evaluate how selection on growth rate alters muscle fiber characteristics and influences postmortem metabolism and subsequent meat quality. Therefore, the objective of this study was to evaluate muscle fiber type, postmortem metabolism and meat quality of Nellore cattle selected for different growth rates. Two-hundred and fifty non-castrated Nellore males differing in post-weaning growth potentials were used. Muscle from 10 high growth potential animals (EPD_H) and 10 low growth potential animals (EPD_L) were analyzed for muscle morphometric profile, postmortem metabolism, and meat quality. EPD_H animals were heavier and had higher hot carcass weight and larger diameter and cross-sectional area of fast oxidative-glycolytic fibers, while EPD_L animals had higher area percentage of slow oxidative fibers. Moreover, EPD_H presented higher glycogen concentrations than EPD_L cattle. Glucose concentrations were higher at 240, 720, and 1440 min postmortem, while G6P was higher from 30 to 1440 min postmortem in EPD_L animals. Finally, EPD_H animals produced less tender meat when compared to that of EPD_L cattle. In conclusion, genetic selection based on growth potential is associate with a shift in fiber type towards a more glycolytic type of muscle that is associated with changes in meat tenderness.

基于生长率的动物选择作为选择指数受到了越来越多的关注。尽管许多人已经评估了生长速率对肌肉特性和肉品质的影响，但很少有研究试图评估对生长速率的选择如何改变肌肉纤维特性并影响死后代谢和随后的肉品质。因此，本研究的目的是评估针对不同生长速率选择的内罗尔牛的肌纤维类型，死后代谢和肉质。使用了205名未-割的内洛尔雄性，其断奶后的生长潜力不同。来自10只高生长潜力动物（EPD _H）和10只低生长潜力动物（EPD _L）的肌肉）进行了肌肉形态分析，事后代谢和肉质分析。EPD _H动物较重，且car体热重较高，快速氧化-糖酵解纤维的直径和横截面积较大，而EPD _L动物具有较慢的氧化纤维的面积百分比。此外，EPD _H的糖原浓度高于EPD _L牛。在EPD _L动物中，死后240、720和1440分钟时葡萄糖浓度较高，而死后30至1440分钟时G6P较高。最后，与EPD _L相比，EPD _H动物产生的嫩肉更少牛。总之，基于生长潜力的遗传选择与纤维类型向更具有糖酵解性的肌肉转变有关，这与肉嫩度的变化有关。