Porcine intramuscular fat content and composition are regulated by quantitative trait loci with muscle-specific effects.

Intramuscular fat (IMF) storage is a biological process with a strong impact on nutritional and technological properties of meat and also with relevant consequences on human health. The genetic architecture of IMF content and composition phenotypes has been thoroughly studied in pigs through the identification of QTL and the estimation of genetic parameters. A question that has not been elucidated yet is if the genetic determinants of IMF-related phenotypes are muscle specific or, conversely, have broad effects on the whole skeletal muscle compartment. We have addressed this question by generating lipid QTL maps for 2 muscles with a high commercial value, gluteus medius (GM) and longissimus thoracis et lumborum (LTL), in a Duroc commercial population (n = 350). Our data support a lack of concordance between the GM and LTL QTL maps, suggesting that the effects of polymorphisms influencing IMF, cholesterol, and fatty acid contents are modulated to some extent by complex spatial factors related to muscle location, metabolism, and function. These results have important implications on the implementation of genomic selection schemes aimed to improve the lipid profile of swine meat.

Quintanilla R ，Pena RN ，Gallardo D ，Cánovas A ，Ramírez O ，Díaz I ，Noguera JL ，Amills M ... -  《-》

Quantitative trait loci analysis of a Duroc commercial population highlights differences in the genetic determination of meat quality traits at two different muscles.

We performed a whole-genome scan with 110 informative microsatellites in a commercial Duroc population for which growth, fatness, carcass and meat quality phenotypes were available. Importantly, meat quality traits were recorded in two different muscles, that is, gluteus medius (GM) and longissimus thoracis et lumborum (LTL), to find out whether these traits are determined by muscle-specific genetic factors. At the whole-population level, three genome-wide QTL were identified for carcass weight (SSC7, 60 cM), meat redness (SSC13, 84 cM) and yellowness (SSC15, 108 cM). Within-family analyses allowed us to detect genome-wide significant QTL for muscle loin depth between the 3rd and 4th ribs (SSC15, 54 cM), backfat thickness (BFT) in vivo (SSC10, 58 cM), ham weight (SSC9, 69 cM), carcass weight (SSC7, 60 cM; SSC9, 68 cM), BFT on the last rib (SSC11, 48 cM) and GM redness (SSC8, 85 cM; SSC13, 84 cM). Interestingly, there was low positional concordance between meat quality QTL maps obtained for GM and LTL. As a matter of fact, the three genome-wide significant QTL for colour traits (SSC8, SSC13 and SSC15) that we detected in our study were all GM specific. This result suggests that QTL effects might be modulated to a certain extent by genetic and environmental factors linked to muscle function and anatomical location.

Gallardo D ，Pena RN ，Quintanilla R ，Ramírez O ，Almuzara D ，Noguera JL ，Amills M ... -  《-》

Response to selection for decreased backfat thickness at restrained intramuscular fat content in Duroc pigs.

Intramuscular fat (IMF) content is a relevant trait for the pig industry and consumers. However, selection for IMF has the undesired correlated effect of decreasing lean growth. A selection experiment was performed to investigate the effects of selection against backfat thickness (BT) at restrained IMF. Barrows from a purebred Duroc line were allocated into a selected (n = 165) or a control (n = 185) group based on their litter predicted EBV. Litters in the selected group were selected against BT at 180 d at restrained IMF in gluteus medius (GM) whereas those in the control group were chosen randomly. Realized selection intensities and genetic responses for BT, IMF in GM, and BW were estimated using a 3-trait multivariate animal mixed model under a Bayesian setting. Correlated responses for other traits were estimated similarly but using a 4-trait model, where other traits were added to the previous 3-trait model 1 at a time. Selected pigs had less BT than control pigs [-1.22 mm, with highest posterior density interval at 95% (HPD95; -2.47, -0.75)] with restrained decrease in IMF, both in GM [-0.16%; HPD95 (-0.36, +0.05)] and in LM [-0.15%; HPD95 (-0.37, +0.09)]. However, the realized selection intensity for IMF in GM denotes that the restriction on IMF was incomplete [-0.18; HPD95 (-0.36, +0.02)]. Selection decreased BW [-1.64 kg; HPD95 (-2.47, -0.75)] but increased carcass lean weight [+0.66 kg; HPD95 (+0.14, +1.22)], indicating that the response in BT offsets the unfavorable correlated response in BW. Selected pigs were shorter [-0.50 cm; HPD95 (-0.81, -0.20)] but with similar ham weight and loin depth. These results provide evidence that lean weight can be improved restraining the genetic change in IMF. However, they also stress that a complete restriction on IMF is difficult to achieve unless selection is practiced on a big population where IMF is accurately predicted.

Ros-Freixedes R ，Reixach J ，Bosch L ，Tor M ，Estany J ... -  《-》

Bayes factor analyses of heritability for serum and muscle lipid traits in Duroc pigs.

Concern about pork quality has increased during last decades. Given the influence of fat content and composition on sensorial, nutritional, and technological variables of pork meat, an accurate knowledge about genetic control of pig lipid metabolism is required. This study focused on providing a broad characterization for serum and meat lipid trait heritability estimates in pigs. Analyses were performed on a population of 370 Duroc barrows and measured the additive polygenic background for the serum concentrations of cholesterol, triglyceride, and low- and high-density lipoproteins at 45 and 190 d of age (at slaughter), as well as intramuscular fat, cholesterol content, and C:12 to C:22 fatty acid content in longissimus thoracis et lumborum and gluteus medius muscles at slaughter. These traits were analyzed under Bayesian univariate animal linear models, and the statistical relevance of heritability estimates was evaluated through Bayes factor (BF); the model with polygenic additive effects was favored when BF >1. All serum lipid traits showed relevant genetic determinism, but the BF reached greater values at 190 d of age. Serum lipid traits displayed moderate modal estimates for heritability that ranged from 0.18 to 0.30. On the other hand, the genetic determinism for meat quality traits showed a heterogeneous behavior with large and less-than-1 BF. In general, longissimus thoracis et lumborum and gluteus medius muscles showed a similar pattern, with strong evidence of polygenic additive effects for intramuscular fat and palmitic, stearic, and cis-vaccenic fatty acids content, whereas oleic and muscle cholesterol content showed moderate to weak BF with moderate heritabilities. Similarly, results regarding linoleic, arachidonic, n-3, and n-6 fatty acids suggested a moderate genetic determinism, but only in gluteus medius muscle. For the remaining traits (myristic and palmitoleic fatty acids in both muscles, along with linoleic, arachidonic, n-3, and n-6 fatty acids in the longissimus thoracis et lumborum muscle), no statistical evidence for genetic control was observed in this study. As a whole, these results confirm the complexity of lipid metabolism in pigs.

Casellas J ，Noguera JL ，Reixach J ，Díaz I ，Amills M ，Quintanilla R ... -  《-》

Quantitative trait loci mapping in an F2 Duroc x Pietrain resource population: I. Growth traits.

Pigs from the F(2) generation of a Duroc x Pietrain resource population were evaluated to discover QTL affecting growth and composition traits. Body weight and ultrasound estimates of 10th-rib backfat, last-rib backfat, and LM area were serially measured throughout development. Estimates of fat-free total lean, total body fat, empty body protein, empty body lipid, and ADG from 10 to 22 wk of age were calculated, and random regression analyses were performed to estimate individual animal phenotypes representing intercept and linear rates of increase in these serial traits. A total of 510 F(2) animals were genotyped for 124 micro-satellite markers evenly spaced across the genome. Data were analyzed with line cross, least squares regression, interval mapping methods using sex and litter as fixed effects. Significance thresholds of the F-statistic for single QTL with additive, dominance, or imprinted effects were determined at the chromosome- and genome-wise levels by permutation tests. A total of 43 QTL for 22 of the 29 measured traits were found to be significant at the 5% chromosome-wise level. Of these 43 QTL, 20 were significant at the 1% chromosome-wise significance threshold, 14 of these 20 were also significant at the 5% genome-wise significance threshold, and 10 of these 14 were also significant at the 1% genome-wise significance threshold. A total of 22 QTL for the animal random regression terms were found to be significant at the 5% chromosome-wise level. Of these 22 QTL, 6 were significant at the 1% chromosome-wise significance threshold, 4 of these 6 were also significant at the 5% genome-wise significance threshold, and 3 of these 4 were also significant at the 1% genome-wise significance threshold. Putative QTL were discovered for 10th-rib and last-rib backfat on SSC 6, body composition traits on SSC 9, backfat and lipid composition traits on SSC 11, 10th-rib backfat and total body fat tissue on SSC 12, and linear regression of last-rib backfat and total body fat tissue on SSC 8. These results will facilitate fine-mapping efforts to identify genes controlling growth and body composition of pigs that can be incorporated into marker-assisted selection programs to accelerate genetic improvement in pig populations.

Edwards DB ，Ernst CW ，Tempelman RJ ，Rosa GJ ，Raney NE ，Hoge MD ，Bates RO ... -  《-》