Table 1.

Effect of different maternal protein levels on early fetal muscle development. Upward-pointing arrow: “increase”; downward-pointing arrow: “decrease”; horizontal arrow: “no change”.

Animals	Experimental Design	Results	Conclusion	References
14 primiparous pure-bred Meishan gilt sbody weight: 36.1 ± 1.8 kg	Digestible energy 13 MJ/kg Control treatment: 12.2% crude protein (CP) (gestation) and 14% CP (lactation) Low protein treatment: 6.1% CP (gestation) and 6.9% CP (lactation)	Muscle protein synthesis: p70S6K and eIF4E ↓ Negative regulator of skeletal muscle development and growth ↑ Muscle weight: Longissimus dorsi muscles ↓	Maternal low protein diet throughout gestation and lactation causes retardation in muscle hypertrophy and protein synthesis	[28]
16 Landrace × Yorkshire crossbred sows in the second parity	Digestible energy:13 MJ/kg (gestation),14.39 MJ/kg (lactation) Control treatment: 15% (CP, gestation) and 18% CP (lactation) Low protein treatment: 7.5% (CP, gestation) and 9% CP (lactation)	Back fat thickness ↓ Restricted amino acid response (AAR) pathway: CHOP, IRE1α, PERK, ATF-6, XBP-1 and Bip, ATF4, and EIF2α↑ Autophagy-related genes: ATG7 and LC3 ↑	Maternal low protein diet throughout gestation and lactation causes offspring reduced adipogenesis and increased lipolysis	[33]
56 German Landrace gilts	Metabolic energy: 13.7 MJ/kg Adequate protein treatment: 12.1% CP High protein treatment: 30% CP; Low protein treatment, 6.5% CP	Total number of myofibers ↔ Myogenic regulatory factors in low protein treatment: MYOG, MRF4, IGF1, IGF1R ↓ Myogenic regulatory factors in high protein treatment: MYOD, MYOG, IGF1R, and IGFBP5 ↑	Moderate high or low maternal protein diets change gene expression but not the phenotype of skeletal muscle from porcine fetuses	[32]
47 pure German Landrace gilts	Metabolic energy: 13.7 ME/kg Adequate protein treatment: 12.1% CP High protein treatment: 30% CP; Low protein treatment, 6.5% CP	Percentage of muscle tissue in in HP in high protein treatment ↑ Primary and secondary myofibers in low protein diet treatment ↓ Subcutaneous adipose tissue mass in low protein diet treatment and high protein diet treatment ↓	Both limited and excess protein supply retards fetal growth, but only limited protein supply impairs myogenesis, persistently restricts muscle growth potential, and favors obesity at infancy.	[30]
24 primiparous German Landrace sows	Metabolic energy: 13.7 ME/kg Adequate protein treatment: 12.1% CP High protein treatment: 30% CP; Low protein treatment, 6.5% CP	Candidate genes of nutrient- dependent pre- and postnatal development: muscular expression of NCAPD2 (LP ↓), NCAPG (↔), NCAPH (LP ↓) Key genes of methionine metabolism: both HP and LP diet significant influence DNMT1 (HP ↑), DNMT3a (LP ↓) and MAT2B (HP ↑)	Maternal protein supply regulate condensin I subunit gene expression by methylation process and in turn may affect cell division in skeletal muscle tissue	[34]