Effects Of Dietary Cottonseed Meal And Cottonseed Oil Supplementation On The Quality Of Egg

Cottonseed meal(CSM)and Cottonseed oil(CSO)are byproducts of cottonseed that are widely used in laying hens.However,the addition of CSM and CSO to laying hens' diets may cause a series of negative effects on egg quality,especially of the yolk,decreasing the commercial value of eggs.The exact mechanism of the egg yolk qualities change that occurred in the eggs from cottonseed-treated hens is not clear.Our research focused on the effects of CSM and CSO on the appearance,palatability,nutritional value,and food safety of eggs and validated the key genes involved in the change of egg yolk qualities in the liver of laying hens to elucidate the biological mechanism.The results of the study are expected to provide guidance for the application of CSM and CSO in laying hen production and to provide a foundation for solving the undesirable characteristics of egg yolk caused by CSM or CSO.A total of 162 19-week-old Hy-line Brown laying hens were randomly allocated into 9 diet treatments with 6 replicates of 3 hens per replicate.A 3×3 factorial design using corn soybean meal based diets supplemented with 0%,6% or 12% cottonseed meal(CSM)and 0%,2% or 4% cottonseed oil(CSO)in place of soybean meal and soybean oil,respectively.After 5 weeks of pre-feeding,the experimental diets were fed for 8 weeks.During the experiment,we collected the eggs to analysis the egg quality,egg yolk texture properties,chemical composition and gossypol residue.The main research results are as follows: 1.Egg qualityThe egg quality parameters include egg weight,protein rate,egg yolk rate,egg shell rate,eggshell thickness,eggshell strength,egg index,and hungh unit were not affected by different levels of CSM and CSO supplementation(P > 0.05).However,the egg yolk color significantly increased(P < 0.05)with an increasing CSM supply,In the CSO group,egg yolk color increased significantly(P < 0.05)only after 8 weeks of feeding.CSM and CSO had no interactions on the egg quality parameters(P > 0.05).The results demonstrated that CSM and CSO have less effect on egg quality.2.Texture properties and structure of egg yolkEggs supplemented with CSM alone showed a clear egg yolk sphere structure,while gel structure was found in the yolk of groups supplemented with 2% and 4% CSO accompanied by a significant increase in hardness(P < 0.05)and springiness(P < 0.05)regardless of whether it contained CSM.In addition,the cohesiveness,gumminess,chewiness and resilience ratio of egg yolk significantly increased(P < 0.05)with an increasing CSO supply.CSM alone did not affect the texture properties,but CSO and CSM had interactions on the cohesiveness,gumminess,chewiness and resilience ratio of egg yolk(P < 0.05).There was a mutually reinforcing effect between CSM and CSO(P < 0.05).There was no significant change in the yolk texture on the fresh eggs and the eggs stored at room temperature for 2 weeks,and also,CSM and CSO had no significant interaction(P > 0.05).The results showed that CSO and the storage conditions are the main factors in causing the changes in the texture of the yolk.The release of these granules from yolk sphere might be the key cause of the increased hardness of the egg yolk.3.The chemical components of egg yolkThe contents of moisture,crude protein,crude fat and phospholipids in the egg yolk obtained from hens which fed with CSM or CSO for 4 weeks and 8 weeks had no significant difference(P > 0.05),however,with the increase of the amount of CSO,the crude protein content of egg yolk showed a decreasing trend(P > 0.05).Also,CSM and CSO had no effects on the contents of amino acid composition,potassium and iron in the egg yolk(P > 0.05),and there was no interaction(P > 0.05)between CSM and CSO supplementation on those trait.Diets consisting of CSM had no significant effect(P > 0.05)on the content of cholesterol,while those containing CSO reduced the content of cholesterol(P < 0.05).CSO significantly increased myristic acid,palmitic acid,stearic acid,linoleic acid and cis-11,14-eicosadienoic acid content in the egg yolk(P < 0.05),significantly reduced the content of the oleic acid,?-linolenic acid,?-linolenic acid and DHA(P < 0.05),the content of n-3 PUFA in the egg yolk decreased significantly,and the content of n-6 PUFA increased significantly(P < 0.05).The effect of CSM on egg yolk fatty acids is highly consistent with that of CSO,but the degree of influence was much lower than CSO.The results showed that CSO is the main factor in causing the changes in the chemical components of egg yolk.4.Gossypol residues in eggsThe free and total gossypol in egg white and in the CSO group was not detected in 4 weeks and 8weeks.Total gossypol residues increased with the increased amount of CSM(P < 0.05),The total gossypol content in the egg yolk was 2.01-2.77 mg/kg(the free gossypol content in the diet was 41.6 mg/kg)and 4.40-5.16 mg/kg(the free gossypol content in the diet was 83 mg/kg).The gossypol residues in the egg yolk had no time response(P > 0.05).There was no significant interaction(P > 0.05)between CSM and CSO supplementation in combination.5.Lipid metabolism in Laying hens' liverCompared with no added CSO group,the expression of SCD mRNA has a decreasing trend with 2% CSO added in the diets(P > 0.05),while significantly decreased at 4% CSO added in the diets(P < 0.05).Compared with the control group,the CSO treatment significantly down-regulated the expression of mRNAs for SREBP1,FGFR3,MTP,VTG,Apo-VLDL-?,ApoB100 in the liver(P < 0.05),and the expression of LR8 mRNA was no significant difference between different groups in the ovaries(P > 0.05).The results found that CSO significantly affects the fat metabolism in the liver of laying hens.CSO affects the quality of the egg yolk by affecting the synthesis,transport,and secretion of lipids in the liver.In a word,the main conclusions of our research are as follows:(1)CSM,CSO and their interaction had no significant impact on the egg quality.(2)CSO increased the content of saturated fatty acids in egg yolk,which promoted the increase of hardness and springiness of egg yolk under 4? storage,CSO might be the key cause of reduced the taste and nutritional value of eggs.Therefore,the addition of cottonseeds and CSO to laying hens' diets should be controlled.(3)The residues of gossypol in the egg yolk resulted from CSM increased with dose response,however,the total gossypol concentration in egg yolk was very low.There was no safety risks in the eggs which obtained from the laying hens fed with diets with 83 mg/kg free gossypol.(4)The changes in egg yolk quality may be related to the changes in synthesis,transport and secretion of lipoproteins in the liver which caused by CSO.