Li Y H, Wei H K, Li F N, Kim S W, Wen C Y, Duan Y H, Guo Q P, Wang W L, Liu H N, Yin Y L
J Anim Sci. 2016 Dec;94(12):5192-5205. doi: 10.2527/jas.2016-0917.
The objective of the study was to explore the extent to which the dietary CP level can be reduced for maintaining muscle protein deposition in growing pigs as well as the related mechanism and whether the response to dietary protein restriction is diversely modified throughout the 2 trial periods. A total of 36 pigs (9.57 ± 0.64 kg initial BW) were individually penned and fed 1 of 3 diets for 10 or 25 d. During each period, the diets contained 20, 17, and 14% CP, respectively. Both the 17% CP diet and the 14% CP diet were supplemented with Lys, Met, Thr, and Trp to provide the same total concentrations as those in the 20% CP diet. Results showed that feeding the 14% CP diet for 10 or 25 d seriously impaired ( < 0.05) growth performance of the pigs compared with those fed the 20 or 17% CP diets. Pigs fed the 20% CP diet for 25 d had a higher ( < 0.05) serum content of urea nitrogen than those fed the 17 and 14% CP diets. In addition, the free AA (FAA) profile in skeletal muscle of the pigs was evidently changed ( < 0.05) by the low-protein diets for 25 d; of note, the 14% CP diet increased ( < 0.05) the size of muscle FAA pool compared with the 20% CP diet. Meanwhile, on d 25, reducing dietary CP levels also influenced ( < 0.05) mRNA levels of specific AA transceptors expressed in skeletal muscle, especially revealing the striking differences between the 14 and 20% CP diet-fed pigs. Most importantly, we observed a globally decreased ( < 0.05) activation of the mammalian target of rapamycin complex 1 (mTORC1) pathway in skeletal muscle of pigs fed the 14% CP diet, whereas only partial inhibition was observed for those fed the 17% CP diet compared with those fed the 20% CP diet. However, feeding the low-protein diets for 10 d had minimal effects on serum parameters, muscle FAA profile, and muscle mTORC1 pathway of the pigs. Taken together, our results indicate that supplementing with limiting AA to the 14% CP diet is not highly effective for the pigs in restoring protein synthesis and muscle growth, whereas the 17% CP diet likely maintains the pigs' muscle mass, which were regulated, at least in part, by mediating AA transceptors expression, FAA profile, and activation of the mTORC1 pathway.
本研究的目的是探讨在生长猪中，日粮粗蛋白（CP）水平可降低到何种程度以维持肌肉蛋白质沉积及其相关机制，以及在两个试验期内，日粮蛋白质限制的反应是否会有不同变化。总共36头猪（初始体重9.57±0.64千克）被单独饲养在栏中，并饲喂三种日粮中的一种，为期10天或25天。在每个时期，日粮分别含有20%、17%和14%的CP。17%CP日粮和14%CP日粮均添加了赖氨酸、蛋氨酸、苏氨酸和色氨酸，以使总浓度与20%CP日粮中的相同。结果表明，与饲喂20%或17%CP日粮的猪相比，饲喂14%CP日粮10天或25天严重损害了（P<0.05）猪的生长性能。饲喂20%CP日粮25天的猪血清尿素氮含量高于饲喂17%和14%CP日粮的猪（P<0.05）。此外，低蛋白日粮饲喂25天明显改变了（P<0.05）猪骨骼肌中的游离氨基酸（FAA）谱；值得注意的是，与20%CP日粮相比，14%CP日粮增加了（P<0.05）肌肉FAA库的大小。同时，在第25天，降低日粮CP水平也影响了（P<0.05）骨骼肌中特定氨基酸转运体的mRNA水平，特别是在饲喂14%和20%CP日粮的猪之间显示出显著差异。最重要的是，我们观察到饲喂14%CP日粮的猪骨骼肌中雷帕霉素靶蛋白复合物1（mTORC1）途径的激活总体下降（P<0.05），而与饲喂20%CP日粮的猪相比，饲喂17%CP日粮的猪仅观察到部分抑制。然而，饲喂低蛋白日粮10天对猪的血清参数、肌肉FAA谱和肌肉mTORC1途径影响极小。综上所述，我们的结果表明，在14%CP日粮中添加限制性氨基酸对猪恢复蛋白质合成和肌肉生长的效果不佳，而17%CP日粮可能维持猪的肌肉质量，这至少部分是通过介导氨基酸转运体表达、FAA谱和mTORC1途径的激活来调节的。
