Meat Quality Comparison Between Pig Breeds And Its Interaction With Nutrition

The objective of this investigation was to study the regulatory mechanism of dietary nutrition underlying the difference of meat quality in different breed swine. The study determined the effects of two swine breeds and two dietary nutritional levels on the growth performance, carcass traits, meat quality, serum parameters, the mRNA levels of IMF deposition related genes in muscle and adipose tissue and the percentage of myofiber type. Moreover, the study evaluated the effects of leptin on fat accumulation of pigs in vitro. There experiments were included in this study:Exp.1Effects of the interaction between breed and nutrition on growth performance, carcass traits, meat quality and myofiber type in longissimus dorsi muscle of pigs.This experiment determined the breed and dietary nutritional levels on porcine growth performance, carcass traits, meat quality and the ratios of mRNA levels of four isoforms of myosin heavy chain (MyHC Ⅰ,Ⅱa, Ⅱb and Ⅱx) in longissimus dorsi muscle by real-time PCR and tried to understand the interaction of breed and nutrition. Sixty Landrace or Wujin pigs were assigned into2nutritional treatments fed diets formulated according to NRC (ND) and Wujin Pig Nutrient Requirement (WD), respectively. These pigs slaughtered at30,60,80and100kg. The average daily gain (ADG), average daily feed intake (ADFI), feed/gain retaio (F/G), fat percentage (FP), muscle percentage (MP), backfat depth (BF), lion eye area (LEA), marbling, drip loss (DL), shear fore (SF) and IMF content were examined.The results showed that:(1) The Landrace fed WD showed decreased ADG but increased F/G at all body weight. The WD fed to Landrace reduced LEA, increased FP, BF and IMF content at100kg compared with ND. Wujin pigs fed WD showed higher ADG at100kg, higher MP and LEA at80and100kg, and higher IMF content at all body weight. The FP, BF and SF of Wujin pigs were decreased by WD at80and100kg.(2) When feeding the same diet, Wujin pigs showed lower ADG, MP, LEA and SF and higher F/G, FP, BF, marbling and IMF content than Landrace.(3) Wujin pigs had more proportion of MyHC Ⅱa and less proportion of MyHC Ⅱx than Landrace. The WD increased the proportion of MyHC Ⅰ and decreased proportion of MyHC Ⅱa and Ⅱx for Wujin pigs but did not alter any proportion of myofiber type for Landrace. Wujin pigs showed higher proportion of total MyHC Ⅰ and Ila but lower proportion of total MyHC Ⅱb and Ⅱx. The WD tended to increase the proportion of total oxidative myofiber type.It was suggested that the breed and dietary nutrition affected the growth performance, carcass traits, meat quality and myofiber type composition of longissimus dorsi muscle. Match of breed and dietary nutrition is required for optimizing phenotypes in pigs.Exp.2The possible regulatory mechanism of dietary nutritional levels on meat quality in different breed pigsThis experiment evaluated the effects of breed and dietary nutritional levels on the serum hormones, lipid metabolites and the mRNA expressions of fat-deposition related genes in subcutaneous adipose tissues and longissimus dorsi muscle by real-time PCR. The results showed that:(1) When Landrace and Wujin pigs were fed the same nutritional diet, Wujin pigs showed decreased insulin and triiodothyronine (T3) at early growth stages. The Wujin pigs had higher serum leptin concentration, free fatty acid (FFA) content and high-density lipoprotein cholesterol (HDL-C), but had lower triglyceride (TG) and total cholesterol (CHO) content compared with Landrace. The WD enhanced the serum leptin concentration and FFA of Wujin and Landrace but reduced TG content compared with ND.(2) The mRNA levels of sterol regulatory element binding protein1c (SREBP-1c), fatty acid synthase (FAS), peroxisome proliferator-activated receptor (PPARy), adipocyte fatty acid-binding protein (A-FABP) and CCAAT/enhancer-binding proteins a (C/EBPa) in adipose tissue of Wujin pigs were higher than those of Landrace fed either WD or ND. But the mRNA levels of hormone-sensitive lipase (HSL), sirtuins1(Sirt1) and forkhead transcription factor O1(FoxO1) genes in adipose tissue of Wujin pigs were lower than those of Landrace fed either WD or ND. Wujin pigs showed had lower mRNA expression of leptin receptor (LEPR) gene at30kg body weight compared with Landrace, but no difference of the mRNA expression of LEPR was observed between Wujin and Landrace at80and100kg. The lipogenic genes expression were up-regulated and lipolytic gene expression were down-regulated by WD during the growth-finishing stages compared with ND in adipose tissue of Landrace and Wujin pigs.(3) The mRNA levels of SREBP-1c, FAS, PPARy, heart fatty acid-binding protein (H-FABP), HSL and C/EBPa in muscle tissue of Wujin pigs were higher than those of Landrace fed either WD or ND. But the mRNA level of FoxO1of Wujin pigs was decreased than that of Landrace. The mRNA expressions of Sirt1and LEPR in muscle tissue were not different between Wujin and Landrace pigs. But the gene expression of LEPR of Wujin pigs fed WD was lower than that of Landrace fed WD at100kg body weight. The WD tended to up-regulated lipogenic gene expression and down-regulated lipolytic gene expression in muscle tissue during the growth-finishing stages compared with ND.(4) There were positive correlation between IMF content and marbling, serum leptin, FFA and HDL-C concentrations, the mRNA levels of H-FABP, PPARy, SREBP-1c, FAS and C/EBPa. But the negative correlations were present between IMF content and SF, serum IGF-I and CHO concentration and the mRNA abundance of LEPR gene.(5) High percentage of oxidative myofiber can increase IMF content and decrease SF and water holding capacity. The oxidative myofiber types and glycolytic myofiber types can be transformed each other.These results suggested that the fat deposition in subcutaneous adipose tissues of Wujin pigs showed higher than that of Landrace pigs, which results from up-regulation of lipogenic gene expression and down-regulation of lipolytic gene expression. While, the increased mRNA expression of both lipogenic gene and lipolytic gene in intramuscular fat tissue of Wujin pigs compared to Landrace pigs, which lead to a net increase in the accumulation of IMF. The increasing IMF content was accompaning with increasing proportion of MyHC Ⅰ and Ⅱa and improving of tenderness. Therefore, the regulatory mechanism of dietary nutritional levels on meat quality in different breed pigs was associated with endocrine hormones, lipid metabolism and thansformation of myofiber types. The leptin may be an important melocular signal role in this process. Exp.3Effects of leptin on lipid metabolism in subcutaneous and intramuscular adipocytesThis experiment determined the effect of leptin on lipid metabolism in subcutaneous and intramuscular adipocytes and the underlying regulating mechanism. The subcutaneous and intramuscular adipocytes were treated with150ng/mL (treatment group) leptin or not (control group) for48hours. The TG, FFA and mRNA levels of SREBP-1c, H-FABP, HSL, LEPR, PPARy and diacylglycerol acyltransferase (DGAT-1) in cells were determined. The results showed that the leptin reduced the TG and FFA content in subcutaneous and intramuscular adipocytes. The mRNA expressions of SREBP-1c, DGAT-1and H-FABP were reduced but those of HSL and LEPR were increased by leptin in subcutaneous and intramuscular adipocytes. However, the leptin did not alter the mRNA expression of PPARy. Moreover, the TG and FFA contents were lower in intramuscular adipocytes than in subcutaneous adipocytes. The mRNA levels of SREBP-1c and DGAT-1were decreased but those of LEPR and HSL were higher in both groups of intramuscular adipocytes compared with of subcutaneous adipocytes. These results suggested that leptin decreased TG accreation by inhibiting lipogenesis and promoting lipolysis. The reduced TG accumulation in intramuscular adipocytes by leptin was due to decresing lipolysis in subcutaneous adipocytes.Taken together, it is concluded that there are differences of growth performance, carcass traits and meat quality between Wujin and Landrace pigs. Due to the interaction of breed and nutrition, the dietary nutrition must match genotype for optimizing phenotype in pigs. The underlying regulatory mechanism of different meat quality is associated with gene expression mediated by leptin in subcutaneous and intramuscular adipocyte and the composition of myofiber types.