早期和后期限饲对肉鸡腓肠肌肌纤维类型和生长轴相关基因表达的影响

Effects of early and late feed restriction on myofiber types and expression of growth-related genes in gastrocnemius of broiler chickens

1日龄三黄雏鸡随机分为自由采食对照组(C)、1-14日龄隔日饲喂的早期限饲组(ER)和50-63日龄隔日饲喂的后期限饲组(LR)。63日龄采腓肠肌外侧头,ATPase染色法及相对定量RT-PCR法检测不同类型肌纤维含量及生长轴相关基因(GHR、IGF-I、IGF-IR)表达。结果表明:E组慢肌纤维含量降低,快肌纤维含量增加,L组无变化。E组慢肌肌球蛋白重链基因表达低于对照组(P<0·05),并伴随生长激素受体(GHR)和胰岛素样生长因子Ⅰ(IGF-ⅠR)mRNA表达的上调(P<0·05),L组无显著变化。提示:早期限饲可对肉鸡生长和肌纤维类型产生长期而且显著的影响,并且涉及肌肉中生长相关基因表达的改变,而后期限饲对肉鸡影响较小,说明早期和后期限饲通过截然不同的机制影响肉鸡肌肉生长。

1-day-old （1 d） broiler chickens were allocated randomly into control （C）, early feed restriction （ER） and late feed restriction （LR） groups. Chickens of group C were fed ad libitum throughout the experiment for 9 weeks, while chickens of group ER and LR were subjected to intermittent feed restriction with feed provided on alternate days for the first and the last 2 weeks of their posthatch life, respectively. 10 chickens from each group were sacrificed at the end of the experiment on 63 d, the lateral gastrocnemius muscle was taken for measuring the cross-sectional areas and densities of slow and fast myofibers with myosin ATPase staining and myofiber typing by relative quantification of mRNA expression for three different types of myosin heavy chain （MyHC） ： slow myofiber MyHC （SM MyHC）, red fast-twitch myofiber MyHC （FRM MyHC） and white fast-twitch myofiber MyHC （FWM MyHC）. Concentrations of growth hormone receptor （GHR）, insulin-like growth factor- I （IGF- I ） and type- I IGF receptor （IGF- I R） mRNA were also determined by RT-PCR using 18S rRNA as an internal-standard. Chickens of group ER exhibited consistently lower body weight throughout the experiment, while chickens of group LR only showed a transient decrease in body weight on 56 d but caught up with their counterparts in group C by 63 d. However, the lateral gastrocnemius muscle weights in both group ER and LR were significantly lower compared with that in the group C. Histological study revealed that the percentage of slow myofibers decreased while that of the fast myofibers increased significantly in group ER compared with the control, whereas no alteration in percentages of slow and fast fibers was observed for group LR. The cross-sectional area of fast fibers differed significantly among three groups. Group LR exhibited the biggest fast fibers, while group ER the smallest. Compared with their control counterparts, group ER exhibited a significant down-regulation for SM MyHC expression, accompanied with significantly higher GHR and IGF- I R mRNA expression in gastrocnemius muscle. In contrast, however, group LR did not show any significant differences in myofiber morphology, myofiber types, or expression of growthrelated genes in comparison with group C. These results indicate that early feed restriction exerts long-lasting and profound influence on muscle growth and myofiber types of broiler chickens, involving changes of mRNA expression for growth-related genes in the muscle. Late feed restriction has only a transient and minor influence on animal growth. Distinct mechanisms seem to underly the effects of feed restriction during different periods of life .