| Liangshan pig belongs to one of the southwest pig breeds called Wujin pig, mainly distributed in Yi Autonomous Prefecture of Liangshan, with the ability of cold and coarse feeding resistance, as well as wonderful meat quality. The meat of Liangshan pig is suitable for processing ham. In recent years, the population of Liangshan pig is declining, in danger of extinction. It is necessary to protect Liangshan pig and utilize this good germplasm resource. In this experiment, we systematically analyzed the growth and carcass performance, meat quality, muscle physiological and biochemical characteristics and nutritional structure of Liangshan pig. Considering the unclear of the suitable slaughter weight of Liangshan pig for the swine industry, we set up seven different fattening weight groups(50 kg,58 kg,66 kg,74 kg,82 kg,90 kg and 98 kg), tested their growth and development, slaughter performance and meat quality traits and physiological and biochemical indexes. We used the Von Bertalanffy model to fit the growth curve of Liangshan pig and found out their growth turning point was day 193.4 within the weight of 62.5 kg. We screened out some candidate functional genes related to pig growth and carcass traits and meat quality. We analyzed the differences of the relative expression level of genes among different slaughter weight and verified the correctness of data of phenotypes through the genetic level. We described the wonderful characteristics of Liangshan pig as well as their suitable slaughter weight, which was between 63 kg and 75 kg. The main conclusions are as follows:1. The growth turning point Liangshan pig is at day 193.4 of age, or 62.5 kg of body weight, then it slowed down. At about fourth (day 180,54.3 kg body weight), fifth (day 194,59.5 kg body weight) or sixth (day 208,65.2 kg body weight) growth and development time point, the growth rate of the body size of Liangshan pig was about to slow down. From day 180 to day 194 (54.3 to 59.5 kg body weight) of age, the feed conversion ratio began to rise slowly, that is, the feed conversion efficiency began to decline. There was no significant difference of feed conversion efficiency among the three time quantums (day 180 to day 194 with the body weight of 54.3 to 59.5 kg, day 194 to day 208 with the body weight of 59.5 to-65.2 kg, day 208 to day 222 with the body weight of 65.2 to 71.8 kg). According to these results, we can conclude that the suitable slaughter weight of Liangshan pig is from 63 kg to 72 kg.2. The average backfat thickness of Liangshan pig is 33.40±5.04 mm, the loin area is 17.68±4.36 cm', the dressing percentage is 75.12±4.09%, the lean meat percentage is 43.81±2.09%, the bone percentage is 12.02±1.00% and the sebum percentage is 45.03±2.74%. The turning point of Liangshan pig's dressing percentage, lean meat percentage, sebum percentage is at 67.4±2.11 kg body weight (the third slaughter weight group) or 74.9±1.25 kg (the fourth slaughter weight group), and from then on, the dressing percentage and lean meat percentage began to reduce, the sebum percentage began to grow slowly. If we slaughter Liangshan pig at this body weight, we can take the advantage of higher dressing percentage and lean meat percentage and lower sebum percentage to gain the highest economic benefit. That is, the suitable slaughter weight of Liangshan pig is from 67.4 kg to 74.9 kg.3. The muscle of Liangshan pig contained various kinds of amino acid, fatty acid, mineral, so the meat has excellent nutritional value, reflected the characteristics of high quality pork. The pH1 of the longissimus dorsi of Liangshan pig is 6.60±0.14, the pH2 is 6.11±0.20; the Minolta L1 is 39.01±3.70, L2 is 42.41±1.66; the drip loss is 3.93±0.18%; the marbling score is 3.33±0.58; the shear force is 4.39±1.20 kg and the cooking rate is 68.26±2.32%. Considering muscle pH, meat colour, marbling, shear force and drip loss, the better meat quality became available at the third slaughter weight group. So, if we use the meat quality as the determination of slaughter weight, we can conclude that the suitable slaughter weight of Liangshan pig should not be lower than 67.4 kg.4. Fluorescence quantitative results showed the significant correlation between the relative expression level of Amelanocortin4 receptor gene (MC4R), insulin-like growth factor 1gene (IGF1), leptin gene(LEP) and the growth and carcass traits; It all so showed the significant correlation between the relative expression level of Calcium-activated neutral protease gene (CAPN1), heart type fatty acid binding protein gene(FABP3) and a AMP activated protein kinase gamma 3 gene (PRKAG3) and the meat quality traits. For the genes associated with growth and carcass traits, the expression pattern of IGF1 gene, PIT1 gene and GH1 gene in the growth and development of Liangshan pig was quite similar, with higher expression in the intermediate slaughter weight group (67.4±2.11 kg, 74.9±1.25 kg and 80.4±1.00 kg) and lower expression in the low (53.2±1.37 kg and 59.5±0:86 kg) and high slaughter weight groups (86.7±0.79 kg and 91.5±1.85 kg) (P<0.05). The expression of LEP and MSTN gene in the intermediate weight group was significantly lower than low and high weight group (P<0.05). Meat quality traits related gene expression analysis showed that with the increase of body weight, intramuscular fat content and other related genes, such as CA3 gene, NME1 gene, FABP3 gene and PDK4 gene expression patterns showed increasing trend of expression level. The significant difference appeared at the third (FABP3 gene) or fourth slaughter weight group (CA3 gene, PDK4 gene) (P<0.05). According to the relative expression pattern of the genes selected; the growth rate became slow and the meat quality has became good ground 70 kg of body weight. So we suggested that Liangshan pig should be slaughtered at about 70 kg.The above results indicated that:The good slaughter performance, meat quality, muscle nutritional constitutes of Liangshan pig contributed to their fine characteristics. Considering varies kinds of economic traits, we conclude that the suitable slaughter weight of Liangshan pig is from 63 kg to 75 kg. |
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