Study On The Biochemistry And Histomorphology Of Intramuscular Fat Deposition In Laiwu Black Pigs

Laiwu black pig with fine meat quality and thick scented fresh meat taste is one of excellent local breeds in China. This paper divided into two experiments: experiment one and experiment two. To observe and analyse the reason of IMF deposition in Laiwu black pigs, seventy-two Laiwu Black and Xin Laiwu pigs (weight of 40~90kg) were used in this paper that explored the mechanism and characteristics of IMF development in Laiwu Black using biochemistry and histology methods. The development changes of intramuscular fatty acids, intramuscular fatty enzymatic activities, muscular adipocytes and muscle fibers were observed at different body weights in Laiwu Black pigs. The results showed as follows:Fatty acid composition: With gaining of body weight, the percentage of total saturated fatty acids were rising and total unsaturated fatty acids were falling, but not significant; Total polyunsaturated fatty acids linolenic acid were falling significantly (P<0.01); Oleic acid was rising significantly (P<0.01), peanutolenic acid was falling firstly, then a little rising and falling lastly; The others were stable. With gaining of body weight, percentage of total SFA and monounsaturated fatty acid, palmitic, palmitoleic acid of Lai wu Black were significantly higher than Xin Laiwu Pig; But total PUFA, stearic, linoleic, peatnutolenic acid were lower than Xin Laiwu Pig; Different body weight of fatty acid composition were different too. Correlation coefficients between total PUFA, lipid and moisture, marbling score were very significant (P<0.01); total PUFA and lose water percentage were significant; total SFA, UFA and marbling score were significant too. The results indicated that oleic acid rising significantly may be helpful to deposition of IMF. Deposition of IMF is relevant to MUFA and PUFA composition in pigs.Intramuscular fatty emzymatic activities: With gaining of body weight, the activity of ICDH was significantly higher than that of MDH in muscle. The activity of ICDH reached a peak at 60~70kg of weight and decreased thereafter. MDH had no significant Development changes. The activity of HSL fell firstly and reached a peak at 70~80kg of weight. The activity of MDH was significantly higher than that of ICDH in backfat. Both MDH and ICDH activities, to some extent, decreased firstly and then increased. The activity of HSL was stable at 40~50kg and then increased gradually. The activity of ICDH was significantly higher than that of MDH in liver. The activities of ICDH and MDH increased firstly and tended to stabilize after 60kg. The activity of HSL had no significant Development changes. The activities of MDH, HSL in muscle were highly correlated toIMF content (?<0.01). MDH, ICDH in liver positively correlated with IMF, and ICDH also with BFT (PO.01). The activities of MDH, HSL in backfat were strongly correlated to BFT (PO.01). It implied that there was not only some immanent contact between the deposition of IMF and BFT via liver, but also some independence from each other. By selecting fatty enzymatic activity in muscle, it is possible to improve IMF content but not to changes BFT.The propensity of IMF deposition between Laiwu Black and Xin Laiwu pigs was similar during early growing period CP>0.05), thereafter, especially between 40~60kg body weight, IMF level of Black Laiwu pigs increase dramatically while Xin Laiwu pigs kept steadily. This indicated that the development of IMF 40~60kg body weight in Black Laiwu pigs may play a meaningful role in deposition of IMF thereafter. The muscular adipocyte diameter enlarged continuously during whole growing period, the average diameter of Black Laiwu was larger than that of Xin Laiwu pigs (P>0.05). To evaluate the changes of adipocyte differentiation at different body weights, the adipocyte fell into three categories according to its diameter: <50um, 50~70um, >70um. At early growing period, the percentage of three categories adipocytes followed the sequence (<50um)>50~70um>(>70um). A high association was found between muscular adipocyte area and IMF level. The results indicated that adipocyte hypertrophy may be important reason of deposition of IMF.With gaining of body weight, the diameter of Laiwu Black pig's muscle fibers were bigger than Xin Laiwu pig, the muscle fibers diameter of Laiwu Black pig were regular, the diameter changes wasn't significant early, but began to rapidly grow at 70kg of weight; muscle fibers of Laiwu Black and Xin Laiwu pigs reached a peak at 40~50kg of weight and then fall; The percentage of red muscle fibers in Laiwu Black pigs were higher than Xin Laiwu pigs and the percentage of white muscle fibers of Laiwu Black pigs were lower than Xin Laiwu pigs, but not significant. At the same body weight, if the percentage of red muscle fibers were higher, deposition of IMF was faster(P<0.05), that indicated the percentage of red muscle fibers is one of reasons that deposition of IMF is fast or slow. Correlation coefficients between red muscle fibers and IMF, marbling score, moisture were very significant (PO.01), that indicated that development of IMF is close to red muscle fibers diameter and the percentage of red muscle fibers.