| Experiment 1 was conducted to determine the effect of different dietary energy sources on hepatic lipid content and induction of Fatty Liver-Hemorrhagic Syndrome in laying hens. One hundred and fifty Lohmann commercial laying hens were divided into three groups of fifty birds each. According to a single factorial arrangement, birds were given one of three experimental diets with control (group 1,2.65Mcal/kg), or high energy diet which was offered with 7% lard (group2,3.06Mcal/kg) and offered with 26% cornstarch (group3, 3.00Mcal/kg). High energy diets decreased feed intake and egg production (P<0.01), average egg weight of group 3 (cornstarch) was decreased (P<0.01). In chicks fed the 7% lard diet or 26% cornstarch ad libitum, hepatic EE (ether extract) and triglyceride were increased significantly comparing with control diet treatment, cornstarch could increase hepatic EE, triglyceride and total cholesterol more significant than lard. The average activity of ALT and AST of high energy was increased to be more than 2 times than control treatment of the last three times blood collection. The LDH of high energy diet was increased with no significant difference of the first three times blood collection, In our experiment, the birds fed the 7% lard diets had thegreastest increase in plasma triglyceride, but there were no significant treatment effects on plasma triglyceride content by cornstarch all the experiment period. The average hemorrhage score of group 2 (lard diet) was the highest in the three groups. In chicks fed the 7% lard diet or 26% cornstarch ad libitum had significantly higher MDA values than the control treatment. In the present study, plasma ALT, AST, LDH activities and TC concentration were positively correlated with hepatic TG concentration (P<0.01). The results showed that measurement of enzyme activities indicative of liver damage in birds, particularly AST, ALT, and plasma TC concentration, is a valuable tool in the diagnosis of fatty liver-hemorrhagic syndrome in a flock of layers, These results suggest that dietary carbohydrate can induce FLHS more efficiently that dietary fat, the hens overfeed high fat diets have significantly proned to more liver hemorrhage than high carbohydrate diets.Experiment 2. The CDS of mtp (3353bp) was cloned and sequenced successfully, from which the primers of realtime PCR were designed for the assessment of the impact of different energy intake on the expression of mtp, srebp-1c, chrebp in liver of layer chicks, the gene ofβ-actin serving as inner reference. The results showed starch could lead to a striking and extremely significant upregulation of srebp-1c (P<0.01) in layer chicks, 258%much higher than control, and tallow could increase its expression (P>0.05). The results also demonstrated starch could result in a significant upregulation of chrebp (P<0.05), but tallow had no significant impact on its expression.After obtaining the CDS of mtp of chick, the sequences in other species, including human, pig, ox, fish, mice, were downloaded from GenBank and analysed. The results showed the sequenced MTP gene exhibited high-level 99.7%homology to a virtual mtp of chick by computer, but a low-level homology to other species. The phylogenetic analysis confirmed that the cloned gene of MTP in this study has a close relative relationship with mtp of chick, but farther from other species.Experiment 3 was conducted to determine the effect of different dietary energy sources (fat and starch) on hepatic lipid deposition and fatty acid synthesis in layer's liver.120 Lohmann pink commercial layers were assigned randomly to 5 treatments of 8 replicates each,3 birds per replicate. All the feed intake of the birds was limited and each bird was fed alone. Five experimental diets were prepared as follows:(1) corn-soybean meal diet as the control, (2) Soybean isolated protein-lard diet, (3) Soybean isolated protein-cornstarch diet, (4) Soybean isolated protein-lard diet plus Metformin 0.55g/d, (5) Soybean isolated protein-cornstarch diet plus Metformin 0.55g/d. All the feed intake of the birds was limited at 90%and 120g/day as the standard, nutrient requirement is based on the Chinese Feeding standard of poultry of 2004.The results showed, starch could increase the content of hepatic EE (ether extract) (P<0.05) and the hepatic cholesterol significantly (P<0.01), no effect on phospholipids (PL). However, the hepatic cholesterol and PL were increased significantly by lard. And lard could improve the ALT level (P<0.01) too, but no significant effect on AST, TG and TC. Compared with the control group, cornstarch could increase plasma AST (P<0.01). With the addition of Metformin, the release of ALT was increased, however the TG of plasrna lipid was increased significantly, and no effect on TC.The lard diets could decrease villus height significantly (P<0.05), and crypt depth was increased significantly (P<0.05) too, but no such role in cornstarch diet, Metformin could decrease the villus height (P<0.01). The activity of lipase in chyme was increased (P<0.01), meanwhile cornstarch improved the activity of amylase in chyme, but no effect on lipase. Metformin had no significant effect on both enzyme activities, but diets with Metformin could decrease the VLDL and ApoB-100 significantly. Both cornstarch and lard diet could reduce the VLDL and ApoB-100 of plasma (P>0.05), compared to the control diets, the VLDL of the cornstarch group was decreased by 9%, and 12%in the lard group.Cornstarch could up-regulate the mtp, srebp-1c and chrebp transcription level (P<0.01), and the lard diet had no such role. The mtp, srebp-1c and chrebp transcription level in cornstarch group was improved 52.8%,26.5%,76.4%respectively. With addition of the Metformin, the srebp-1c and chrebp decreased significantly, but no effect on mtp. Cornstarch diet could also improve the activity of ACC and FAS significantly. However, the lard diet could lead to the decrease of the ACC activity, but no effect on FAS. Metformin had no effect on FAS but the activity of CPT-1 was improved significantly. The lard diet could increase the activity of CPT-1 (P<0.01).There were no significant effect on the activity of LPC and G-6-P in both cornstarch and lard group. Metformin had decreased both the LPC and G-6-P level in cornstarch group and lard group(P>0.05).These results showed that dietary carbohydrate could induce hepatic lipid deposition by increasing the ACC and FAS activity and up-regulating the srebp-1c and chrebp transcription levels in the layer's liver much easier than dietary fat, and high carbohydrate diets make layers more prone to fatty liver. |
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