Metabolic and histochemical characteristics of fat and muscle tissues in homozygous or heterozygous pigs for the body composition QTL located on chromosome 7

Production performance, carcass composition, and adipose tissue traits of heavy pigs: influence of breed and production system

Both breed and production systems are responsible for production efficiency and quality traits of pork. Effects of breed and production system within breed on growth, body fatness, and adipose tissues traits were assessed in the pure Basque (B, nonselected, local French) and conventional Large White (LW) breeds, reared either in a conventional (C, slatted floor), alternative (A, indoor straw bedding and outdoor area), or extensive (E, free range) system. A total of 100 castrated males were produced in 2 replicates, each involving 50 pigs distributed in 5 treatments based on breed and production system (i.e., BC, BA, BE, LWC, and LWA [10 pigs/group and per replicate]). From 35 kg BW to slaughter at around 145 kg BW, the BC, BA, LWC, and LWA pigs received the same growing and finishing diets, whereas the BE pigs had free access to the natural resources of the E pen and received a standard growing-finishing diet at restricted allowance according to the farming practices of the B pork chain. The B pigs had lower (P < 0.001) ADG and G:F than the LW pigs and were much older (P < 0.001) at slaughter. The LWA pigs had similar ADG but lower (P = 0.03) G:F than the LWC. Within the B breed, the BA had higher (P = 0.04) and the BE lower (P < 0.001) ADG compared with BC pigs. The B pigs had a higher (P < 0.001) carcass dressing an exhibited around 2-fold higher (P < 0.001) back fat proportion, perirenal fat weight and LM lipid content than the LW pigs. Compared with C, the A system decreased (P = 0.04) carcass dressing within LW but did not influence carcass traits within B pigs. The E system decreased (P ≤ 0.05) carcass dressing, back fat proportion, and LM lipid content in BE compared with BC pigs. The B pigs exhibited larger (P < 0.001) adipocytes in both subcutaneous adipose tissue (SCAT) and LM than the LW pigs. Malic enzyme activity was higher in SCAT of B than LW pigs despite their greater fatness, and was higher (P ≤ 0.01) in BA but lower (P < 0.001) in BE than in BC pigs. The B pigs had higher (P < 0.001) MUFA but lower (P ≤ 0.006) SFA and PUFA fatty acid percentages in SCAT than the LW pigs. Compared with C, the A system had scarce influence on FA composition within each breed, whereas the E system led to lower (P = 0.015) SFA and greater (P < 0.001) PUFA in SCAT of the B pigs. Altogether, the E production system can counteract the genetic potential of B pigs for growth rate but also body fatness.

Preadipocyte and adipose tissue differentiation in meat animals: influence of species and anatomical location

Early in porcine adipose tissue development, the stromal-vascular (SV) elements control and dictate the extent of adipogenesis in a depot-dependent manner. The vasculature and collagen matrix differentiate before overt adipocyte differentiation. In the fetal pig, subcutaneous (SQ) layer development is predictive of adipocyte development, as the outer, middle, and inner layers of dorsal SQ adipose tissue develop and maintain layered morphology throughout postnatal growth of SQ adipose tissue. Bovine and ovine fetuses contain brown adipose tissue but SQ white adipose tissue is poorly developed structurally. Fetal adipose tissue differentiation is associated with the precocious expression of several genes encoding secreted factors and key transcription factors like peroxisome proliferator activated receptor (PPAR)γ and CCAAT/-enhancer-binding protein. Identification of adipocyte-associated genes differentially expressed by age, depot, and species in vivo and in vitro has been achieved using single-gene analysis, microarrays, suppressive subtraction hybridization, and next-generation sequencing applications. Gene polymorphisms in PPARγ, cathepsins, and uncoupling protein 3 have been associated with back fat accumulation. Genome scans have mapped several quantitative trait loci (QTL) predictive of adipose tissue-deposition phenotypes in cattle and pigs.

Breed-specific lipid-related gene expression in the subcutaneous fat of Large White and Erhualian pigs at weaning

Abstract. The Erhualian (EHL) pig possesses significantly lower growth rates and higher adipose deposition compared with the Large White (LW) pig. To further understand the mechanism of breed lipid deposition difference at the early postnatal age, we employed an animal model of EHL and LW pigs at weaning age to compare the lipid metabolism differences in subcutaneous fat. The result showed that serum triglyceride in EHL was significantly higher (P < 0.05) than that of LW. Peroxisome proliferator-activated receptor-γ protein level in EHL was significantly higher (P < 0.01) though CCTTA enhancer-binding protein level demonstrated no change compared with LW pigs. Hormone sensitive lipase, adipose tissue triglyceride lipase mRNA expression and the lipase activity were significantly lower (P < 0.05) in EHL. Uncoupling protein-2 protein content was significantly lower (P < 0.01) in EHL than that in LW pigs. We first cloned the nucleotide sequence of Zinc-α2-glycoprotein (ZAG) with 1090 bp and found that both ZAG mRNA expression and protein level in EHL pigs was significantly lower (P < 0.01) than that of LW pigs. β3 adrenergic receptor mRNA expression in EHL pigs was significantly higher (P < 0.01) than that of LW pigs, though tumour necrosis factor α gene expression demonstrated no significant difference. Therefore, the significant breed lipid metabolism difference in subcutaneous fat exists at an early postnatal age between EHL and LW pigs, and this difference may originate from two causes including the increased lipid synthesis and reduced lipid mobilization in EHL pigs compared with LW pigs.

Towards candidate genes affecting body fatness at the SSC7 QTL by expression analyses

A quantitative trait locus (QTL) affecting fatness in a way opposite to expectations based on breed means was mapped to swine chromosome 7 (SSC7) using crosses between Large White (LW) and Meishan (MS) founders. Defining the molecular fatness trait more explicitly would allow deducing positional candidate genes, for which expression differences must be analysed in experimental populations. First, mRNA levels of genes representing sequential steps in adipogenesis or involved in lipid metabolism were studied in backfat of pigs having homozygous LW(QTL7)/LW(QTL7) or heterozygous LW(QTL7)/MS(QTL7) alleles and considered at two ages. mRNA level of DLK1 expressed in preadipocytes was greater in MS(QTL7)/LW(QTL7) pigs than in homozygous pigs at 28 days. Transcript abundances of CEBPA involved in differentiation, the prolipogenic FASN gene and the adipocyte-specific marker FABP4 were lower in MS(QTL7)/LW(QTL7) pigs compared with LW(QTL7)/LW(QTL7) pigs at 150 days. Because these results suggest a lag time in terminal differentiation associated with the MS allele, seven genes in the QTL interval were deduced as promising candidates for the QTL effect by bioinformatics analysis. Among them, PPARD and CDKN1A had lower expression levels in MS(QTL7)/LW(QTL7) pigs at both ages. Genotype-related differences were observed in mRNA levels of PPARD target genes involved in cell differentiation (FZD7) or fatty acid oxidation (ACADL and ACOX1) at 150 days. These results re-evaluate the potential of PPARD to explain part of variation in pig adiposity.

Mapping quantitative trait loci for metabolic and cytological fatness traits of connected F2 crosses in pigs

In the present study 3 connected F(2) crosses were used to map QTL for classical fat traits as well as fat-related metabolic and cytological traits in pigs. The founder breeds were Chinese Meishan, European Wild Boar, and Pietrain with to some extent the same founder animals in the different crosses. The different selection history of the breeds for fatness traits as well as the connectedness of the crosses led to a high statistical power. The total number of F(2) animals varied between 694 and 966, depending on the trait. The animals were genotyped for around 250 genetic markers, mostly microsatellites. The statistical model was a multi-allele, multi-QTL model that accounted for imprinting. The model was previously introduced from plant breeding experiments. The traits investigated were backfat depth and fat area as well as relative number of fat cells with different sizes and 2 metabolic traits (i.e., soluble protein content as an indicator for the level of metabolic turnover and NADP-malate dehydrogenase as an indicator for enzyme activity). The results revealed in total 37 significant QTL on chromosomes 1, 2, 4, 5, 6, 7, 8, 9, 14, 17, and 18, with often an overlap of confidence intervals of several traits. These confidence intervals were in some cases remarkably small, which is due to the high statistical power of the design. In total, 18 QTL showed significant imprinting effects. The small and overlapping confidence intervals for the classical fatness traits as well as for the cytological and metabolic traits enabled positional and functional candidate gene identification for several mapped QTL.

Cellularity of developing subcutaneous adipose tissue in Landrace and Meishan pigs: adipocyte size differences between two breeds

Experiments were designed to compare the adipocyte cellularity of subcutaneous adipose tissue between growing Landrace (low backfat) and Meishan (high backfat) pigs at 1 week, 3 weeks, 6 weeks, 3 months and 5 months of age. As pigs aged, body weight and backfat thickness of both breeds significantly increased. When compared at equal ages, backfat thickness adjusted to equal body weight was greater for Meishan pigs. The mean diameter of fat cell size also increased with age, and by 6 weeks adipocytes from both outer and inner layers of subcutaneous adipose tissue were larger in Meishan pigs. At 5 months, approximately 80% of the adipose tissue mass in Meishan pigs was attributable to adipocytes measuring 95-165 µm in diameter, whereas adipocytes of 75-145 µm comprised most of the tissue mass in the Landrace. Although the contribution of smaller adipocytes (25-45 µm) to the tissue volume was negligible, both breeds showed a biphasic diameter distribution at all ages, suggesting that adipocyte hyperplasia is still active. Our results demonstrate that cellularity differences exist between the subcutaneous adipose tissues of Landrace and Meishan pigs, and adipocyte hypertrophy is the most overwhelming contributor to the greater backfat deposition for Meishan pigs.

Genome-wide mapping of quantitative trait loci for fatness, fat cell characteristics and fat metabolism in three porcine F2 crosses

Background

QTL affecting fat deposition related performance traits have been considered in several studies and mapped on numerous porcine chromosomes. However, activity of specific enzymes, protein content and cell structure in fat tissue probably depend on a smaller number of genes than traits related to fat content in carcass. Thus, in this work traits related to metabolic and cytological features of back fat tissue and fat related performance traits were investigated in a genome-wide QTL analysis. QTL similarities and differences were examined between three F₂ crosses, and between male and female animals.

Methods

A total of 966 F₂ animals originating from crosses between Meishan (M), Pietrain (P) and European wild boar (W) were analysed for traits related to fat performance (11), enzymatic activity (9) and number and volume of fat cells (20). Per cross, 216 (M × P), 169 (W × P) and 195 (W × M) genome-wide distributed marker loci were genotyped. QTL mapping was performed separately for each cross in steps of 1 cM and steps were reduced when the distance between loci was shorter. The additive and dominant components of QTL positions were detected stepwise by using a multiple position model.

Results

A total of 147 genome-wide significant QTL (76 at P < 0.05 and 71 at P < 0.01) were detected for the three crosses. Most of the QTL were identified on SSC1 (between 76-78 and 87-90 cM), SSC7 (predominantly in the MHC region) and SSCX (in the vicinity of the gene CAPN6). Additional genome-wide significant QTL were found on SSC8, 12, 13, 14, 16, and 18. In many cases, the QTL are mainly additive and differ between F₂ crosses. Many of the QTL profiles possess multiple peaks especially in regions with a high marker density. Sex specific analyses, performed for example on SSC6, SSC7 and SSCX, show that for some traits the positions differ between male and female animals. For the selected traits, the additive and dominant components that were analysed for QTL positions on different chromosomes, explain in combination up to 23% of the total trait variance.

Conclusions

Our results reveal specific and partly new QTL positions across genetically diverse pig crosses. For some of the traits associated with specific enzymes, protein content and cell structure in fat tissue, it is the first time that they are included in a QTL analysis. They provide large-scale information to analyse causative genes and useful data for the pig industry.

Haplotypes of the porcine peroxisome proliferator-activated receptor delta gene are associated with backfat thickness

BACKGROUND

Peroxisome proliferator-activated receptor delta belongs to the nuclear receptor superfamily of ligand-inducible transcription factors. It is a key regulator of lipid metabolism. The peroxisome proliferator-activated receptor delta gene (PPARD) has been assigned to a region on porcine chromosome 7, which harbours a quantitative trait locus for backfat. Thus, PPARD is considered a functional and positional candidate gene for backfat thickness. The purpose of this study was to test this candidate gene hypothesis in a cross of breeds that were highly divergent in lipid deposition characteristics.

RESULTS

Screening for genetic variation in porcine PPARD revealed only silent mutations. Nevertheless, significant associations between PPARD haplotypes and backfat thickness were observed in the F2 generation of the Mangalitsa x Piétrain cross as well as a commercial German Landrace population. Haplotype 5 is associated with increased backfat in F2 Mangalitsa x Piétrain pigs, whereas haplotype 4 is associated with lower backfat thickness in the German Landrace population. Haplotype 4 and 5 carry the same alleles at all but one SNP. Interestingly, the opposite effects of PPARD haplotypes 4 and 5 on backfat thickness are reflected by opposite effects of these two haplotypes on PPAR-delta mRNA levels. Haplotype 4 significantly increases PPAR-delta mRNA levels, whereas haplotype 5 decreases mRNA levels of PPAR-delta.

CONCLUSION

This study provides evidence for an association between PPARD and backfat thickness. The association is substantiated by mRNA quantification. Further studies are required to clarify, whether the observed associations are caused by PPARD or are the result of linkage disequilibrium with a causal variant in a neighbouring gene.