Effect Of Dietary Energy Density On Intramuscular Fat Deposition For Pigs And Its Underlying Mechanism

Intramuscular fat(IMF) is generally associated with the pork quality.Study on nutritional regulation on pork quality is the hot area of modern animal nutrition..To understand the relationship between dietary energy level and pork IMF and its mechanism, the present study investigated the effect of energy level on IMF deposition and the activities and gene expressions of FAS and HSL.Three experiments have been conducted as followings.Exp.1 Effect of Dietary Energy Density on Performance,Pork Quality and Biochemical Indicators of Growing-finishing Pigs72 Danish Landrace×Rongchang crossbred pigs with average weight of 20 kg were randomly allocated into 3 treatments(6 replicates per treatment and 4 pigs per replicate).The digestible energy levels of diets were 11.75,13.05 and 14.36MJ/kg,respectively.The pigs were slaughtered at 100 kg body weight.The result showed that:(1) There were no significant effects of energy density on average daily gain(ADG) and average daily feed intake(ADFI) (P＞0.05),while feed conversion ratio was improved(P＜0.05) and the duration of finishing was shortened(P＜0.05).The percentage of external fat,backfat thickness and intramuscular fat were increased(P＜0.05),but other parameters of pork quality were not influenced.(2) The triglyceride and total cholesterol in serum rose gradually with energy density increasing. There was no significantly difference for serum triglyceride among the treated groups.The total cholesterol of 14.36 MJ/kg energy density was significantly increased compared to group of 11.75 MJ/kg energy density.Exp.2 The Mechanism of Dietary Energy Density to Regulate IMF Deposition of Growing-finishing Pigs The experiment was designed as Exp.1.The pigs were slaughtered at 100 kg body weight to examine the activities and gene expressions of FAS and HSL.The result showed that:(1) Energy density affected the activity of FAS.Compared with low-energy density group,the activities of FAS in fat tissue in middle-energy density group and high-energy density group were increased by 19.4%(P＞0.05) and 41.9%(P＜0.01),respectively;the activities of FAS in the liver in middle-energy density group and high-energy density group were increased by 6.6%(P＞0.05) and 31.49%(P＜0.01),respectively,and the activity of FAS in high-energy density group was significantly higher than that of middle-energy density group(P＜0.01);the activities of FAS in muscle in middle-energy density group and high-energy density group were increased by 208.4%(P＜0.01) and 769.9%(P＜0.01), respectively,and the activity of FAS in high-energy density group was significantly higher than that of middle-energy density group(P＜0.01).The activity of FAS in fat tissue was higher than that in liver and muscle.(2) Energy density affected the activity of HSL in different tissues.The activities of HSL in different tissues were increased with energy density increasing(P＞0.05).The activity of HSL in fat tissue was higher than that of liver and muscle (P＜0.O1).(3) The expressions of FAS mRNA in fat tissue and muscle were increased with energy density increasing.Compared with low-energy density group,the FAS mRNA expressions in fat tissue of middle-energy density group and high-energy density group were increased by 13.9%(P＞0.05) and 42.3%(P＜0.05).There were no significant effects of energy density on the expression of FAS mRNA in muscle(P＞0.05).The expression of FAS mRNA in fat tissue was obviously higher than that in muscle for pigs fed the same diet.(4) The expressions of HSL mRNA in fat tissue and muscle were decreased with energy density increasing.Compared with low-energy density group,the HSL mRNA expressions in fat tissue of middle-energy density group and high-energy density group were decreased by 15.7%(P＜0.05) and 23.8%(P＜0.05);the HSL mRNA expression in muscle of middle-energy density group and high-energy density group were decreased by 13.6%(P＜0.05) and 22.6% (P＜0.05).The expression of HSL mRNA in fat tissue was higher than that in muscle for pigs fed the same dietary(P＜0.01).(5) The ratio of FAS mRNA/HSL mRNA was increased with energy density increasing.The ratios of FAS mRNA / HSL mRNA in fat tissue of middle-energy density group and high-energy group were increased by 30%(P＞0.05) and 85%(P＜0.05) compared to low-energy density group.The ratios of FAS mRNA/HSL mRNA in muscle tissue of middle-energy density group and high-energy group were increased 46.2% (P＞0.05) and 88.5%compared to low-energy density group.(6) There were significantly positive correlations(P＜0.05) between energy density and intramuscular fat,FAS mRNA and the ratio ofFAS mRNA/HSL mRNA.Exp.3 Effect of Energy Levels on Cell Growth and Expressions of FAS mRNA and HSL mRNA of PreadipocytesThe experiment was designed as a single factorial arrangement.Glucose was used as energy source.There were 3 treated groups and the glucose concentrations were 0,0.25%and 0.5%respectively.There were 6 repeats per group.Cell growth and expressions of FAS mRNA and HSL mRNA at 16h and 32h were detected.The results showed that:(1) At 16h and 32h,the cell growth was improved with the glucose levels increasing.(2) The expressions of FAS and HSL mRNA were improved with the glucose levels increasing.At 16h,the 0.5% glucose improved significantly the mRNA expression of FAS(P＜0.01) and HSL(P＜0.05).At 32h,the 0.5%glucose also improved significantly the mRNA expression of FAS(P＜0.05) and HSL(P＜0.05).The results suggested that the suitable glucose levels could promote the cell growth of preadipocyte and the expressions of fatty-deposition-related genesIt was concluded based on the above results that dietary energy level could influence IMF deposition in pigs and the underlying mechanism was associated with the regulation on the activities and gene expressionsof FAS and HSL.