| Sex effect |
| Gilt or barrow | - Belly proportion in the carcass: higher in barrow- Lean meat proportion in belly: higher in gilt | Stupka et al. (2004) |
| Gilt or barrow | - Back fat thickness: higher in barrow- Firmness: softer in gilt- Fatty acid composition • ↓ Saturated fatty acids (SFA) and ↑ linoleic acid and polyunsaturated fatty acids (PUFA) in gilt • ↑ Iodine value (IV) in gilt | Correa et al. (2008) |
| Gilt or barrow | - Belly proportion in the carcass: higher in barrow- Meat and fat in the belly (%) • Higher meat proportion in gilt belly • Higher content of fat in barrow belly | Bahelka et al. (2011) |
| Gilt or barrow | - Belly weight: heavier belly in barrow- Firmness: softer in gilt- Fatty acid composition • ↑ Palmitic acid and ↓ linolenic acid in barrow • ↑ IV in gilt | Lee et al. (2013) |
| Gilt or barrow | - Weight, width, and thickness: heavier, wider, and thicker belly in barrows- Firmness: firmer belly in barrows | Overholt et al. (2016) |
| Castrated methods |
| Immunocastrated (IC) males, surgically castrated (SC) males, entire males, females | - pH: IC>SC and females- Color of IC: ↓ CIE L* value than SC and ↑ CIE a* value than SC and females- Water holding capacity: IC<SC- Cooking loss: females≥SC≥IC=entire males- Fat content: highest in SC and lowest in entire males belly- Visual evaluation: higher score in IC and females belly- Sensory evaluations • Tenderness: lower in entire males • Juiciness: higher in SC • Overall acceptability: higher in SC and lower in entire males | Jeong et al. (2011) |
| Physically castrated (SC), IC, entire male, or gilt | - Width: widest belly in IC barrows fed ractopamine hydrochloride- Thickness: thicker belly in SC barrow than entire male- Firmness • Highest flop distances in belly of SC barrow • No differences between IC fed ractopamine and gilts • Lowest flop distance in belly of entire male- Fatty acid composition • ↑ IV in entire male and no difference between IC and gilt • ↓ SFA and monounsaturated fatty acids (MUFA) and ↑ PUFA in entire male | Kyle et al. (2014) |
| Physically castrated (SC) or IC and ractopamine hydrochloride diet | - Thickness: thicker belly in SC- Firmness (flop): softer belly in IC | Lowe et al. (2016) |
| Gilt, IC, or SC barrow | - Proximate content: ↑ protein content and ↓ lipid content in IC than SC- Color: ↑ CIE a* value in gilt belly meat- Backfat thickness: higher in IC than gilt- Fatty acid composition • ↑ PUFA, omega-3, and omega-6 in IC than SC • ↓ SFA in gilt than SC • ↑ IV in gilt and IC | Costa e silva et al. (2017) |
| SC males, entire females, IC females | - Belly proportion (%): highest in SC males- Firmness: firmer belly in SC males- Proximate content: ↑ dry matter and fat and ↓ moisture and protein in SC males- Fatty acid composition • SFA and MUFA were not significantly different between sexual types Ȃ ↑ ↟ Linoleic acid and PUFA in entire females and IC females • IV: entire females≥IC females≥SC males | Font-i-Furnols et al. (2023) |
| IC males or entire males | - Belly length: longer belly in IC males- Firmness: Firmer belly in IC males- Fatty acid composition • ↑ SFA and ↓ PUFA, PUFA/SFA ratio, and IV in IC males | Font-i-Furnols et al. (2023) |
| SC or IC barrow | - Width: wider belly in IC- Thickness: thicker belly in SC- Firmness (flop): tended to firmer belly in SC | Tavárez et al. (2014) |
| Time intervals between second Improvest® dose and slaughter- 9, 7, or 5 week before slaughter | - Thickness: increases linearly as time interval increase- Fatty acid composition • ↑ PUFA and IV as time interval decrease | Harris et al. (2018) |
| Genetic effect, genotype |
| Stress genotype- Negative=NN (halothane-free), carrier=Nn, or positive=nn (homozygous recessive for the halothane gene) | - Firmness: increased in stress-negative genotype- Proximate content: ↓ moisture and protein and ↑ lipid in stress-negative genotype | Swan et al. (2001) |
| Genotype, IGF2-G3072A mutation- Heterozygous (AG) or homozygous (AA) | - Thickness: thicker belly in AG pigs than AA pigs- Firmness: firmer belly in AG pigs- IV: tended to higher IV in AA pigs | Clark et al. (2014) |
| Genotype, CRTC3-p.V515F mutation- GG, TG, or TT | - Intermuscular fat thickness: thinner in pigs with the TT genotype- Total muscle area: greater in pigs with heterozygous genotype (GG and TT)- Total fat percentage: TG>GG>TT | Lee et al. (2018) |
| Genetic effect, breed |
| Sire line- Hampshire (HA)×Pietrain (PN), Landrace (LA), or Yorkshire (YO)×PN | - Belly proportion in the carcass: LA>HA×PN>YO×PN- Meat and fat in the belly (%) • HA×PN: highest percentage of meat • YO×PN: highest percentage of fat, skin, and bones | Bahelka et al. (2011) |
| Two-way crossbreeds- Yorkshire×Landrace (YL), Yorkshire×Berkshire (YB), or Yorkshire×Chester White (YC) | - pH: lowest in YC- Proximate content: ↓ moisture content in YB belly- Cooking loss: lower in YB- TBARS values: higher in YB at 14 d- Fatty acid composition • YL: ↑ stearic acid, oleic acid, and MUFA • YB and YC: ↑ myristic acid, linoleic acid, linolenic acid, and n-6 fatty acids • YC: ↑ PUFA- Free amino acid composition: ↑ concentrations of most free amino acids in YB- Sensory evaluation: higher score in YC | Lim et al. (2013) |
| Three-way crossbreeds- Yorkshire×Landrace×Duroc (YLD), Yorkshire×Chester White×Yorkshire (YCY), and Yorkshire×Berkshire×Duroc (YBD) | - Proximate content: highest moisture content in YCY belly- Sensory evaluation: higher score in YLD | Lim et al. (2014) |
| Sire line- Pietrain or Duroc ancestry | - Thickness: thicker belly in Duroc sired pigs- Firmness: greater flop distance in Duroc sired pigs | Lowell et al. (2019) |
| Breed- Landrace×Yorkshire ×Duroc (LYD) or novel pig breed (Woori Heukdon, WHD) | - Belly yield (%): higher in WHD- Proximate composition: ↑ fat content and ↓ moisture, protein, and collagen in WHD- Cooking loss: lower in WHD- Color: ↓ CIE L* value and ↑ CIE a* value in WHD- Fatty acid composition • ↑ MUFA and UFA and ↓ SFA in WHD- Volatile aroma composition • ↑ Compounds associated with fatty odor in WHD • ↑ Compounds associated with rosty ordor in LYD | Hoa et al. (2023) |
| Genetic line effect- Sire or dam line- Estimated breeding value- Feed efficiency: low, intermediate, or high | - Belly weight: heaviest belly in sire high efficiency group- Thickness: thickest belly in sire high efficiency group | Saikia et al. (2024) |
| Growth performance |
| Growth rate Slaughter weight | - Back fat thickness: higher with weight increase- Fatty acid composition • ↑ PUFA:SFA ratios and n-6:n-3 ratios in slow growing • ↑ Stearic fatty acid and SFA proportions in fast growing | Correa et al. (2008) |
| Carcass weight | - Thickness: thicker belly with increase carcass weight- Firmness: firmer belly with increase carcass weight- IV: decreased IV with increase carcass weight | Harsh et al. (2017) |
| Fat levels | - Belly yield: higher yield with increased fat level- Proximate composition: ↑ fat and ↓ moisture, protein, and collagen in high fat level- Color: ↑ CIE b* value in high fat level- Cooking loss: decreased with increased fat level- Fatty acid composition • ↑ Oleic acid and ↓ PUFA in high fat level- Volatile aroma composition • ↑ Maillard reaction-derived flavor compound (meaty and roasty flavors) in low fat level group • ↑ Oleic acid-derived compounds (fatty and oily flavors) in high fat level group- Sensory properties: higher score in high fat level group | Hoa et al. (2021) |
| Fatness and genetic effect- F1: 12.3%–25.9%, F2: 26.0%–33.9%, and F3: 34.0%–47.1% of fat content from commercial pigs- F4: 36.4%–56.3% of fat content from Duroc pigs- F5: 55.0%–69.1% of fat content from Iberian×Duroc barrows | - Belly weight: heaviest in F5 and lightest in F1 pigs- Belly proportion: lowest in F5 and no significant difference between commercial pigs (F1-3)- Length: increased across the bellies from F1 to F4- Width: lowest in F5 and no significant difference between F1-F4- Firmness: firmer belly in F5 and softer belly in F1- Proximate composition: ↑ lipid content and ↓ moisture, protein, and ash content with increased fatness- Fatty acid composition • ↑ SFA and MUFA and ↓ PUFA with increased fatness in commercial pigs • ↑ Oleic acid and ↓ linoleic acid in F5- IV: F1>F2>F3>F4>F5 | Albano-Gaglio et al. (2024) |