Effects Of Stocking Density On Duck Growth,Stress And Cecal Microflora Diversity In Deep Litter System

Deep litter system is a feed style that could combine the duck breeding process with the litter microecological cycle system.Duck excrement provides carbon source for the proliferation of litter microflora.Duck excrement is degraded by litter microflora and provides a comfortable and warm environment for the duck.The system can control the discharge of duck excrement and achieves the purpose of reducing the pollution of excrement accumulation.Commercial farming pursues greater economic benefits.High stocking density can improve the utilization rate of the duck pens and achieve higher productivity.However,it is limited by the efficiency of litter microbial degradation.Therefore,it is important to choose a suitable stocking density for obtaining high benefit and high quality products.In this study,we first compared the duck production performance in different density groups at 4 to 8 weeks.The gene expression changes in duck liver were obtained by RNA-seq technology.Finally,the 16S r DNA sequencing technology was used to detect the microflora structure and abundance of cecum and litter.Through these methods,the effects of different stocking densities on production performance,liver stress,metabolism,and cecal microflora diversity of duck were explored in the deep litter system.This study clarified the effect of litter microflora on cecal microflora.The appropriate stocking density of the deep litter system was determined.This study provided reference data for the application and promotion of deep litter system.The main results showed that:(1)With the ducks grow up,the growth and trends of each stocking group was roughly the same.When the stocking density was 4 ducks/m~2,the best meat production performance(the slaughter rate was 88.35%,the lean meat rate was 27.08%),fat deposition(the sebum rate was 21.97%,the abdominal fat rate was 1.51%)and feed conversion rate(3.10:1)could be obtained.However,the average daily gain(49.02 g)and the final weight of ducks(2.76 kg)were obtained when the stocking density was 5ducks/m~2.Moreover,compared with 4 ducks/m~2,the production performance indexes such as average daily intake,feed conversion rate,livability and slaughter rate,semi-eviscerated rate and eviscerated rate were not much different(4 ducks/m~2:the average daily feed intake was 150.48 g,the survival rate was 98.03%,the slaughter rate was 88.35%,the semi-clearance rate was 80.62%,and the total clearance rate was 72.45%.5 ducks/m~2:the average daily feed intake was 152.60 g,the feed conversion rate was 3.12:1,the survival rate was 98.22%,the slaughter rate was 87.69%,the semi-clean rate was 80.52%,and the total clean rate was 72.55%).When the stocking density was 6 ducks/m~2,there was a certain degree of negative impact on the performance of meat ducks,but the difference did not reach a significant level(P>0.05).(2)Stocking density had no significant effect on blood biochemical indexes of ducks(P>0.05).73 differentially expressed genes in liver were screened out at 6 weeks.At 8weeks,628 differentially expressed genes were enriched.The differentially expressed genes in liver were enriched in the RIG-I-like receptor signaling pathway,Toll-like receptor signaling pathway and NOD-like receptor signaling pathway.In addition,a large number of genes and pathways were enriched,which were related to metabolism,such as the coding genes of AMPK,Protein kinase C family.Differentially expressed genes participate in the body’s metabolic activities through enrichment into the processes of glucose metabolism,lipid metabolism and energy metabolism,such as Insulin signaling pathway,Adipocytokine signaling pathway,Pentose and glucuronate interconversions and Biosynthesis of amino acids.(3)The dominant bacteria at the cecal microflora phylum level were Firmicutes(59.61%)and Bacteroidetes(33.96%).At the genus level were Bacteroides(22.82%)and Ruminococcaceae UCG-014(6.09%).There was no significant difference in the structure and relative abundance of cecal microflora between different stocking densities,and the difference occurred between ages.The dominant bacteria at the phylum level were Proteobacteria(38.06%)and Bacteroidetes(29.38%)in litter.At the genus level were Truepera(4.63%)and Pricia(4.01%).The relative abundance of phylum and genus levels varied during the three growth stages of ducks,but the difference was not significant.It was found that the duck cecal microflora and litter microflora in each period were relatively independent.The dominant bacteria at the genus level is completely different.The litter microflora was more complex and abundant than that of cecum.The number of OTUs in the litter is almost twice of the cecum.There are few OTUs in common,and the number of common OTUs decreases with the growth of ducks.In summary,the stocking density of 6 ducks/m~2had some negative effects on the performance of meat ducks,but it did not reach a significant level(P>0.05).A large number of metabolism-related differentially expressed genes and pathways were enriched in the liver,and suggesting that changes in stocking density may be related to meat production performance,fat deposition and meat quality of ducks.The stocking density had no significant effect on the structure and abundance of cecal microflora.There was no correlation between cecal microflora and litter microflora.