| For the increasingly lack of the protein feed resources, cotton meal is considered to be animportant source of protein feed, but as a result of the existence of gossypol, a kind of toxicingredients, limits its application in the production of laying hens. In order to better use ofcotton meal and provide theoretical support to guarantee the healthy and production of layinghens, this study explores the effect of gossypol on production performance and liver lipidmetabolism of laying hens through six experiments.In exp.1, the range of variation of free gossypol level in commercial cotton meal wasresearched. Forty-three samples was collected in major cotton producing areas across thecountry in the test. The results showed that the variation of free gossypol content in cottonmeal was very big and the content of some samples are over the limit of country lettingstandard. The average content of crude protein in cotton meal is42.34%, and the variablecoefficient is10.39%.In exp.2, the effect of low level gossypol diets on production performance and liverlipid metabolism of laying hens was studied. Two hundred and seventy Hy-line varietybrown laying hens (23-W old) were randomly subjected to one of the following three groupsfor45weeks: the content of free gossypol in the diet was0mg/kg,20mg/kg and40mg/kgrespectively. The results showed that laying hens feeding with gossypol diet for long-terminduced the accumulation of free gossypol in the liver, lead to disorder of liver cell structure,damage of mitochondria and endoplasmic reticulum and with different degree of steatosis.Compared with the control group, long-term feeding with low level gossypol diets have nosignificantly effect on production performance and laying performance, but significantlyincreased the mortality and elimination rate and deepened yolk colour. Liver-carnitinepalmitoyltransferase1(L-CPT1) mRNA level of liver was up-regulated significantly by long-termfeeding with low level gossypol diets, while acetyl-CoA carboxylase1(ACC1), fatty acidsynthase(FAS), sterol regulatory element binding proteins1c(SREBP-1c) mRNA level ofliver were down-regulated significantly by long-term feeding with low level gossypol diets.In exp.3, the effect of high level gossypol diets on production performance and liverlipid metabolism of laying hens was studied. Two hundred and sixty-four Hy-line variety brown laying hens (26-W old) were randomly subjected to one of the following two groupsfor50weeks: the content of free gossypol in the diet was0mg/kg、200mg/kg respectively.The results showed that laying hens feeding with high level gossypol diet for long-termresulted in liver injury and increased liver fat deposits. Compared with the control group,200mg/kg free gossypol in diet significantly increased the mortality and elimination rate oflaing hens and significantly reduced the average weight of eggs, deepened yolk color.However, the rate of yolk in the egg with gossypol diet was increased significantly. High levelgossypol in diet enhanced the content of total cholesterol(CHOL) and high density lipoproteincholesterol(HDL-C),and also enhanced the activity of total antioxidant capacity(T-AOC),CuZn-superoxide dismutase(CuZn-SOD) in plasma of laying hens. Analysis of some relatedgenes expression showed that, CuZn-SOD and glucose regulated protein78(GRP78), genesrelated with liver injury, mRNA level was down-regulated significantly by long-term feedingwith high level gossypol diets. And L-CPT1gene which related with lipid oxidation, it’smRNA level was also down-regulated significantly by long-term feeding with high levelgossypol diets. At the same time, content of non-esterified fatty acid(NEFA) in plasma wasincreased, but NEFA in liver was significantly suppressed.In exp.4, the effect of free gossypol on liver injury and lipid metabolism of layinghens was studied. Twenty-four Hy-line variety brown laying hens (58-W old),which havenever fed by diet containing gossypol, were randomly subjected to one of the following twogroups for14days: intraperitoneal injection of acetate gossypol (20mg/kgBW/d, dissolved withDMSO and saline), control group treated with the dissolvent in the same volume. The resultsshowed that free gossypol induced serious pathologic liver damage and dysfunction, so that itwas obvious swelling and hardening with fatty degeneration. Compared with the controlgroup, free gossypol significantly decreased the average body weight, feed intake and layingrate. The level of glutamic-pyruvic transaminase(ALT) and glutamic-oxalacetictransaminase(AST) in plasma of laying hens with Intraperitoneal injection of free gossypolsignificantly increased, but the activity of glutathione peroxidase(GSH-Px), catalase(CAT) and thecontent of NEFA, very low-density lipoprotein(VLDL) in plasma was significantly decreased.Compared with the control group, free gossypol significantly up-regulated stearic aciddehydrogenase1(SCD1)、 apolipoprotein B100(apoB100)、 apolipoprotein VLDL-II(apoVLDL-II) and L-CPT1mRNA level of liver.In exp.5, the effect of vitamin A and Fe on free gossypol induced the change ofproduction performance and liver lipid metabolism of laying hens was studied. Twohundred and seventy Hy-line variety brown laying hens (23-W old) were randomly subjected to three groups for45weeks, the content of free gossypol in the basic diet was40mg/kg, andthe supplement of VA and Fe in the treatment group was8000IU/kg and40mg/kg. The resultsshowed that supplement with40mg/kg Fe in diet containing40mg/kg free gossypolsignificantly increased the laying rate and improved the mortality and elimination rateinduced by free gossypol. However, deepened yolk color and down-regulated SREBP-1cmRNA level by long-term feeding with low level gossypol diet was not obviously improvedby supplement of Fe. VA could improve the mortality and elimination rate induced by freegossypol, but the laying rate and average egg weight was not obviously affected bysupplement of VA in gossypol diet, and that VA significantly increased the yolk color basedon the gossypol effect.In exp.6, the effect of choline and soyabean lecithin on free gossypol induced thechange of production performance and liver lipid metabolism of laying hens was studied.Three hundred and ninety-six Hy-line variety brown laying hens (26-W old) were randomlysubjected to three groups for50weeks, the content of free gossypol in the basic diet was200mg/kg, and the supplement of choline and soybean lecithin in the treatment group was0.05%and0.2%. The results showed that there were no significantly effect on laying rate andfeed intake of laying hens for supplement with0.05%choline chloride and0.2%soybeanlecithin in200mg/kg free gossypol diet, and it could not improve the decreased egg weightand deepened yolk color induced by long-term feeding with high level free gossypol diet. Butcholine significantly increased the content of CHOL, LDL-C and triglyceride(TG) in plasmaand obviously decreased content of VLDL in liver of laying hens feeding with gossypol diet.Compared with the200mg/kg free gossypol diet group, ACC1and CuZn-SOD、Mn-SOD、GRP78mRNA level of liver was up-regulated significantly by choline. Supplement with0.2%soybean lecithin in200mg/kg free gossypol diet could improve the mortality andelimination rate of laying hens induced by long-term feeding with high gossypol level diet.And supplement with soybean lecithin in gossypol diet could obviously decrease content ofVLDL in liver and down-regulate apoB100and peroxisome proliferator-activated receptor α(PPARα) mRNA level of lver.In conclusion, long-term feeding with containing gossypol diet can result inaccumulation of free gossypol in liver of laying hens. And the gossypol toxicity can inducedifferent levels liver injury, decrease egg weight and increase the mortality and eliminationrate. The gossypol toxicity also affect the liver lipid metabolism of laying hens. The possiblemechanism maybe concerned with the decrease of fatty acid synthesis in liver and this effectis due to the change of capacity of fatty acid synthesis regulated by SREBPs. High free gossypol level can suppress β-oxidization of fatty acid, decrease fat utilization in liver, andthe regulation approach of this effect may not be through PPARα pathway. Acute poisoningof free gossypol can enhance the ability of fatty acid synthesis and lipoprotein assembly inliver of laying hens, but the ability of lipoprotein transport does not change. Supplement ofFe in containing gossypol diet can efficiently improve the harmful effect on productionperformance of laying hens induced by gossypol. Supplement of choline and soybean lecithinin containing gossypol diet is beneficial for abnormal lipids metabolism in liver of laying hensinduced by gossypol. |
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