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Summary Intramuscular fat (IMF) content is a critical indicator of pork quality that affects directly the purchasing desire of consumers. However, to measure IMF content is both laborious and costly, preventing our understanding of its genetic determinants and improvement. In the present study, we constructed an accurate and fast image acquisition and analysis system, to extract and calculate the digital IMF content, the proportion of fat areas in the image (PFAI) of the longissimus muscle of 1709 animals from multiple pig populations. PFAI was highly significantly correlated with marbling scores (MS; 0.95, r2 = 0.90), and also with IMF contents chemically defined for 80 samples (0.79, r2 = 0.63; more accurate than direct analysis between IMF contents and MS). The processing time for one image is only 2.31 s. Genome‐wide association analysis on PFAI for all 1709 animals identified 14 suggestive significant SNPs and 1 genome‐wide significant SNP. On MS, we identified nine suggestive significant SNPs, and seven of them were also identified in PFAI. Furthermore, the significance (−log P) values of the seven common SNPs are higher in PFAI than in MS. Novel candidate genes of biological importance for IMF content were also discovered. Our imaging systems developed for prediction of digital IMF content is closer to IMF measured by Soxhlet extraction and slightly more accurate than MS. It can achieve fast and high‐throughput IMF phenotype, which can be used in improvement of pork quality.

Background Currently, meat cut traits are integrated in pig breeding objectives to gain extra profit. However, little is known about the heritability of meat cut proportions (MCP) and their correlations with other traits. The aims of this study were to assess the heritability and genetic correlation of MCP with carcass and meat quality traits using single nucleotide polymorphism chips and conduct a genome-wide association study (GWAS) to identify candidate genes for MCP. Results Seventeen MCP, 12 carcass, and seven meat quality traits were measured in 2012 pigs from four populations (Landrace; Yorkshire; Landrace and Yorkshire hybrid pigs; Duroc, and Landrace and Yorkshire hybrid pigs). Estimates of the heritability for MCP ranged from 0.10 to 0.55, with most estimates being moderate to high and highly consistent across populations. In the combined population, the heritability estimates for the proportions of scapula bone, loin, back fat, leg bones, and boneless picnic shoulder were 0.44 ± 0.04, 0.36 ± 0.04, 0.44 ± 0.04, 0.38 ± 0.04, and 0.39 ± 0.04, respectively. Proportion of middle cuts was genetically significantly positively correlated with intramuscular fat content and backfat depth. Proportion of ribs was genetically positively correlated with carcass oblique length and straight length (0.35 ± 0.08 to 0.45 ± 0.07) and negatively correlated with backfat depth (− 0.26 ± 0.10 to − 0.45 ± 0.10). However, weak or nonsignificant genetic correlations were observed between most MCP, indicating their independence. Twenty-eight quantitative trait loci (QTL) for MCP were detected by GWAS, and 24 new candidate genes related to MCP were identified, which are involved with growth, height, and skeletal development. Most importantly, we found that the development of the bones in different parts of the body may be regulated by different genes, among which HMGA1 may be the strongest candidate gene affecting forelimb bone development. Moreover, as previously shown, VRTN is a causal gene affecting vertebra number, and BMP2 may be the strongest candidate gene affecting hindlimb bone development. Conclusions Our results indicate that breeding programs for MCP have the potential to enhance carcass composition by increasing the proportion of expensive cuts and decreasing the proportion of inexpensive cuts. Since MCP are post-slaughter traits, the QTL and candidate genes related to these traits can be used for marker-assisted and genomic selection.

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Background Pork cutting is a very important processing in promoting economic appreciation in the pig industry chain. The purpose of this study was to investigate the proportion and weight of carcass cuts, and to analyze the effects of breeds or hybrids, sex and carcass weight on meat cuts. Simultaneously, explore the correlation between meat segmentation and carcass traits. Methods The sampled pigs were raised in Muyuan Food Co., Ltd. (Henan, China) under constant and consistent feeding environment and uniformly slaughtered at 180 days following standard pig slaughter processing. A total of 2,000 pigs from four genotypes of Landrace (LD), Yorkshire (YK), Landrace × Yorkshire (LY) and Duroc × Landrace × Yorkshire (DLY) were sampled and measured for 19 classes carcass cuts traits including its weights and proportions and 10 carcass traits relating to carcass length and back fat products. Effects of carcass weight, sex and genotype on meat cuts and carcass traits were investigated by linear model using home-made R scripts. Results The proportion of the middle cut increasing and proportion of the shoulder and leg cut decreasing as carcass weights increasing. More specifically, proportion of backfat increased the highest and the thickness of four-point backfat was significantly increasing with carcass weights increasing, which hint that fat deposition is the major step in the late growth stage. Besides, the proportion of shoulder cut and backfat in barrows are significantly higher than that in sows, while the leg cut is the opposite. The proportion of the middle cut and shoulder cut are the highest in LD and DLY respectively. We also found that the effects of carcass weight, sex and breed for carcass traits are consistent with cutting meats. Furthermore, the correlation between the proportions of most cutting meats and carcass traits was low. Conclusions The effects of carcass weight, sex and genotype on the weight and proportion of most cutting meats and carcass traits reflect the characteristic of breeds and its differential character of growth to fatten developments between sex. The above results laid an important foundation for the breeding of pig carcass composition.