Abstract：The determination and evaluation of carcass performance and meat quality traits are the foundation of the development and utilization of pig (Sus scrofa) germplasm resources, and the red muscle fibers and white muscle fibers encoded by MyHC genes are positively correlated with the tenderness and juiciness of pork. In order to facilitate the rational utilization and promotion of newly cultivated lean-type Rizhao large white (RZW) pigs, 34 fattening RZW pigs were slaughtered to detect carcass performance and meat quality. The traits including carcass performance, meat quality and nutrient content traits and so on were measured and compared with these of Yimeng black (YM), Large white (LW) and Yorkshire Guanzhong black (YG) pigs. Futher, the expression level of myosin heavy chain genes MYH1, MYH2, and MYH4 were also examined in leg muscle and dorsal muscle of RZW and Meishan (MS) pigs. The results showed that the 75.43% of slaughter rate, 32.79% of leg hip ratio and 67.32% of lean meat rate of RZW pigs have no significant difference with LW pigs, but significantly higher than local varieties YM and YG pigs. RZW pigs showed significant heterosis and genetic complementarity on carcass performance. But on meat quality traits, meat color scored 4.4 points and the intramuscular fat content 1.54%, have improved compared with LW pigs. However, the ability of fat deposition is significantly weaker than that of YM pigs, and the meat is less tasty. In nutrients, RZW pigs had rich in amino acids. The total amino acids and essential amino acids content are Extremely higher than that of YM , LW and YG pigs. However, The overall fatty acid content of RZW pigs was significantly lower than that of the other three breeds. The results also showed the expression of MYH1 and MYH2 in the leg muscle of RZW pigs was significantly higher than that of the back muscle, and the expression of MYH2 was significantly higher than that of Meishan pigs. In addition, it is interesting the expression of three types of MyHC genes in dorsal muscle of RZW pigs was lower than that in MS pigs. Thus, the new breed RZW pigs had good performance of meat production and rich nutrition, but meat quality needs to be further improved. This study provided the foundation for the reasonable continuous breeding, marketing and utilization of RZW pigs. And the results of MyHC genes expression in RZW and MS pigs might provide the theoretical basis on meat quality molecular mechanism.
