Effects Of Different Molecular Weight Chitosans On Lipid Metabolism Of Frizzled Chickens And Its Underlying Mechanisms

Chitosan is an alkaline polysaccharide with positive charge in the nature, and it exhibits potent hypolipidemic and hypocholesterolemic effect in both animals and human. This study was conducted to investigate the effects of dietary supplementation with different molecular weight chitosans on growth, slaughter performance, meat quality, antioxidant activity, lipid metabolism, also investigate the lipid metabolism mechanisms through the lipase activity in digestive tract and the activity or gene expression of Fatty acid synthase(FAS), Lipoprotein lipase(LPL), Hepatic lipase(HL) and Hormone sensitive lipase(HSL) in the liver or abdominal fat.A total of 192 49-day-old female Frizzled Chicken were randomly divided into 4 groups(control group, low molecular weight group, medium molecular weight group and high molecular weight group) with 8 replicates per group and 6 chickens per replicate by body weight using a completely randomized design. The experiment lasted for 42 d. The control groups were fed with corn-soybean meal basal diet, and the others with basal diet plus 0.75% chitosan with molecular weight of 2 k Da, 5 k Da and 50 k Da, respectively. Results showed as follows:(1) There was no significant differently in average daily gain(ADG), average daily feed intake(ADFI), the feed conversion ratio(F/G), dressed rate, chamber half net rate, all eviscerated rate between the groups(P>0.05), but all groups which feed with chitosans showed a lower abdominal fat, liver fat and Intermuscular fat width while compared with the control group(P<0.05), and the liver fat in medium- and low molecular weight groups was lower than that in high molecular weight group(P<0.05). Compared with the control group, the high molecular weight groups reduced the drumstick rate significantly(P<0.05), but no obvious difference in the medium- and low molecular weight groups(P>0.05).(2) There was a tendency of decreasing drip loss of breast muscle in broilers(P<0.1). However, chitosans did not affect meat colour, p H values or shear force(P>0.05).(3) Serum TG was decreased in the medium molecular weight group, while serum Total-Cholesterol(TC) was lower in both high- and low molecular weight groups(P<0.05).(4) The low molecular weight chitosan did not affect serum Triglyceride(TG) and TC. The serum nonestesterified fatty acid(FFA) was showed a trend to decrease by chitosan(P>0.05). All three chitosan supplementations decreased serum Low-density lipoprotein cholesterol(LDL-C) and increased serum High-density lipoprotein cholesterol(HDL-C)(P<0.05).(5) The high- and medium molecular weight chitosans increased fecal fat excretion and decreased fat absorption(P<0.05). However, low molecular weight chitosan did not influence fecal fat and fat absorption(P>0.05). Also Chitosans with different molecular weight could effectively inhibit activity of pancreatic lipase(P<0.05).(6) Dietary supplementation of different molecular weight chitosans could significantly reduce liver FAS activity(P<0.05), but there was no significant difference in m RNA level(P>0.05). Chitosans with molecular weight of 2 k Da and 5 k Da could significantly increase liver LPL and HL activity, and it show a trend to enhance LPL m RNA level(P<0.1). Chitosans did not affect the activity of abdominal fat HSL, but the low molecular weight chitosan increased the activity of abdominal fat LPL(P<0.05).(7) Serum Malondialdehyde(MDA) level in chitosan groups was significantly lower than that in the control, and Superoxide dismutase(SOD) activity was significantly higher(P<0.05).In conclusion, we found that chitosan with molecular weight of 2 to 50 k Da did not affect growth and meat performance, but trended to improve meat quality by decreasing drip loss of breast muscle in Frizzled Chickens. Three molecular weight of chitosans exhibited a similar inhibiting effect on body fat deposition in broilers. The lipid-lowering effects of 50 k Da chitosan might be mediated by reduced dietary lipid absorption. The 2 k Da chitosan was useful in improving fat metabolism, while 5 k Da chitosan appeared to play a hypolipidemic role via both ways mentioned above. The three chitosans regardless of molecular weight had effective in improving antioxidant activity in Frizzled Chickens.