Abstract
BackgroundTo investigate the effects of dietary crude protein (CP) restriction on muscle fiber characteristics and key regulators related to protein deposition in skeletal muscle, a total of 18 growing-finishing pigs (62.30 ± 0.88 kg) were allotted to 3 groups and fed with the recommended adequate protein (AP, 16 % CP) diet, moderately restricted protein (MP, 13 % CP) diet and low protein (LP, 10 % CP) diet, respectively. The skeletal muscle of different locations in pigs, including longissimus dorsi muscle (LDM), psoas major muscle (PMM) and biceps femoris muscle (BFM) were collected and analyzed.ResultsResults showed that growing-finishing pigs fed the MP or AP diet improved (P < 0.01) the average daily gain and feed: gain ratio compared with those fed the LP diet, and the MP diet tended to increase (P = 0.09) the weight of LDM. Moreover, the ATP content and energy charge value were varied among muscle samples from different locations of pigs fed the reduced protein diets. We also observed that pigs fed the MP diet up-regulated (P < 0.05) muscular mRNA expression of all the selected key genes, except that myosin heavy chain (MyHC) IIb, MyHC IIx, while mRNA expression of ubiquitin ligases genes was not affected by dietary CP level. Additionally, the activation of mammalian target of rapamycin complex 1 (mTORC1) pathway was stimulated (P < 0.05) in skeletal muscle of the pigs fed the MP or AP diet compared with those fed the LP diet.ConclusionThe results suggest that the pigs fed the MP diet could catch up to the growth performance and the LDM weight of the pigs fed the AP diet, and the underlying mechanism may be partly due to the alteration in energy status, modulation of muscle fiber characteristics and mTORC1 activation as well as its downstream effectors in skeletal muscle of different locations in growing-finishing pigs.Electronic supplementary materialThe online version of this article (doi:10.1186/s40104-016-0106-8) contains supplementary material, which is available to authorized users.
Highlights
To investigate the effects of dietary crude protein (CP) restriction on muscle fiber characteristics and key regulators related to protein deposition in skeletal muscle, a total of 18 growing-finishing pigs (62.30 ± 0.88 kg) were allotted to 3 groups and fed with the recommended adequate protein (AP, 16 % CP) diet, moderately restricted protein (MP, 13 % CP) diet and low protein (LP, 10 % CP) diet, respectively
The average daily gain (ADG) was decreased (P < 0.01) with the dietary protein level reduction, and improved (P < 0.01) F:G was observed in pigs fed the MP or AP diet compared with those fed the LP diet
In terms of the skeletal muscle mass weight, psoas major muscle (PMM) and biceps femoris muscle (BFM) did not show any significant differences among the treatments, whereas a trend to significance (P = 0.09) was noted in longissimus dorsi muscle (LDM) of pigs fed the MP diet compared with those fed the AP or LP diet
Summary
To investigate the effects of dietary crude protein (CP) restriction on muscle fiber characteristics and key regulators related to protein deposition in skeletal muscle, a total of 18 growing-finishing pigs (62.30 ± 0.88 kg) were allotted to 3 groups and fed with the recommended adequate protein (AP, 16 % CP) diet, moderately restricted protein (MP, 13 % CP) diet and low protein (LP, 10 % CP) diet, respectively. The skeletal muscle, which accounts for 20–50 % of total body mass, is the primary metabolic tissue, contributing up to 40 % of the resting metabolic rate [1, 2]. It acts as an endocrine organ, regulating the disposal of nutrient and energy consumption in the body by secreting myokines, such as interleukin (IL)-6 and IL-15 [3, 4]. Mammalian target of rapamycin complex 1 (mTORC1) plays a key role in protein synthesis of skeletal muscle [6, 7], and constitutively consist of mTOR, regulatory associated protein of mTOR (Raptor), and mLST8/GβL [8, 9]. Protein deposition depends on the balance between the rates of protein synthesis and degradation
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