| Objective: Cottonseed and its processed products are not only having high nutritional value,but also rich in resources,they are important feed resources in China.However,they contain free gossypol(FG)and cyclopropenoid fatty acid(CPFA),which limits their usage in Livestock and poultry feed.Particularly,it is believed that excessive supplementation of them will cause "rubber eggs" formation.However,the key ingredient in cottonseed contributing to "rubber egg" formation is controversial,and focus on FG and CPFA.Besides,the biological mechanism of "rubber egg" formation is still unclear.Thus,the study intends to verify the following issues through feeding trials: 1.To study the effects of cottonseed oil(CSO)and cottonseed meal(CSM)on production performance,egg quality and health of laying hens;2.To identify the key dietary factor that causing "rubber egg";3.To illuminate the biological mechanisms of "rubber egg" production.Experiment 1 The effects of CSO and CSM on production performance,egg quality and health of laying hensBased on a "corn + soybean meal + soybean oil" diet,three levels of CSO(0%,2% and 4%) and CSM(0%,6% and 12%) were set.By using a 2 × 3 factor design,162 24-week-old hy-line brown layers were randomly assigned to 9 treatments.The feeding trial lasted for 8 weeks.During the trial,data of production performance were recorded daily and egg quality were tested every two weeks.After the experiment,serum samples were collected and biochemical indexes were tested.The results show that:1)Supplementation of 12% CSM(FG = 83.3 mg/kg) significantly increased yolk color and shell thickness(P < 0.05) of eggs,but had no significant impact on production performance and health of laying hens.2)Supplementation of CSO(58 mg/kg ≤ CPFA ≤ 116.0 mg/kg) slightly increased yolk color(P < 0.01);significantly reduced(P < 0.01) hen day egg production,average egg weight and feed efficiency of laying hens;significantly increased the contents of creatinine(P < 0.01),total protein(P < 0.01),albumin(P < 0.01),glucose(P < 0.05) and cholesterol(P < 0.01)in serum.Experiment 2 Effect of CSO and CSM on physical properties and components of egg yolkIn order to clarify the key dietary factor leading to the production of "rubber eggs" and to preliminarily clarify the mechanism of its formation,the physical properties and main components of eggs were analyzed.The boiled yolks under different storage conditions were measured using a texture analyser.A rheometer was used to detect the changes of viscosity and elasticity of eggs during the heating process.The fatty acid composition in egg yolk was detected by GC-MS.Protein content and composition of yolks were detected by BCA protein detection kit and SDS-PAGE,respectively.The results show that:1)Cottonseed oil supplementation,which significantly increased the hardness,springiness and chewiness of boiled yolks(P < 0.01),is the key dietary factor leading to the production of "rubber egg".Besides,cold storage for 2 weeks interacted(P < 0.01) with the CSO intake to promote this phenomenon.2)Supplementation of CSO had no significant effect on the viscosity and elasticity of egg yolk in liquid and gel state,but it increased the elasticity of egg yolk after heating and solidifying(P < 0.05).3)Supplementation of CSO did not cause the deposition of CPFA in egg yolks,but it significantly increased the content of saturated fatty acid(P < 0.05)with a decrease of monounsaturated fatty acid(P < 0.05).4)Supplementation of CSO significantly increased the content of total protein in yolk(P < 0.05),and change the composition of protein in yolk granules and plasma(P < 0.05).Experiment 3 The effect of CSO on gene expression in the liverTo further clarify the biological mechanism of "rubber egg" production,after feeding trial,the livers of three hens in each treatment were randomly collected,RNA was extracted and detected by RNA-sequence.The results show that:1)Supplementation of CSO up-regulated the expression of the gene encoding apolipoprotein A in the liver,thereby could improve the transport capacity of HDL in the blood.2)Supplementation of CSO significantly changed the expression of genes encoding hsp70,hsp90,hsp110 and CRYAA,which could change the spatial conformation of proteins by affecting the modification of proteins.3)Supplementation of CSO significantly down-regulated genes encoding solute carriers and sodium-potassium pumps,which could affect ion metabolism.4)Supplementation of CSO significantly up-regulated the gene expression of the enzyme encoding acetyl-coA and the enzyme promoting acetyl-coA to enter the fatty acid synthesis pathway,which could promote the synthesis of saturated fatty acid in the liver.In summary,the following conclusions are drawn in this experiment:1)Adding no more than 12% CSM with FG content less than 83.26 mg/kg has no significant adverse effect on the production and health of laying hens.2)CSO intake affected production performance and health of laying hens;impacted the composition of lipoprotein in the yolk,and lead to the production of "rubber eggs".Therefore,the total CSO content in the layers’ diet is not recommended to exceed 2%,and the content of CPFA should be less than 58 mg/kg.3)CPFA supplementation affected the fatty acid synthesis,protein structure modification and lipoprotein transportation,which could make changes in the structure and composition of lipoproteins in egg yolk.These changes could influence the chain expansion and intermolecular bonding during heating,increase the hardness and elasticity of the yolks after solidifying,and eventually lead to "rubber egg". |
