Effects Of Sound Sources And Stocking Densities On Behavior And Physiology Of Green Shell Layers

Farm animals provide humans with important agricultural products such as meat,milk,eggs and fur.Their production performance is directly related to the economic benefits,and their health and welfare status are also related to product quality.As common farm animals,laying hens have received widespread attention for their production performance,health,and welfare status.Sound sources and stocking densities are common factors which can influence the breeding of laying hens.Massive researches of the two factors have been conducted on the other farm animals,while studies on the production performance,reproductive traits,stress hormones,behavior,and intestinal health in laying hens are still very limited,and the interactions of the two factors are kept unknown.Xiandao green shell layers were selected as the laboratory animal.A 3×3 factorial design with three stocking densities and three sound sources was used for the study.The conventional stocking density applied in intensified chicken farms in China is 450-500 cm2/bird.Accordingly,the stocking densities were set as low density(LD,892 cm2/bird),medium density(MD,510 cm2/bird),and high density(HD,357cm2/bird).The sound sources were natural sound(NS),instrumental music sound(IMS),and mixed road sound(MRS),respectively.The experiment contained 9 treatment groups with 6 replicates for each group.Laying performance,egg.quality,yolk deposition,reproduction-related hormones and gene expression were tested to estimate the production performance of green shell layers,while stress hormones,behaviors and intestinal microorganisms were also analyzed to evaluate the health and welfare status,so as to provide theoretical basis for keeping the balance between production performance and animal health.The main findings are as follows:(1)There were no significant effects on the average egg weight,egg shape index,egg shell thickness,and yolk color of green shell layers in different sound sources and stocking densities.While MRS treatment significantly decreased the egg production rate during 7-18 d of the experiment,it also significantly.reduced the relative yolk weight and Haugh unit.IMS had no significant impact on egg production rate compared to NS groups,but was significantly higher than MRS groups during 13-18 d.During 1-18 d,egg production rate of LD treatment increased,while HD treatment significantly decreased.In addition,relative eggshell weight of MD treatment was highest.Overall,mixed road sound source and high stocking density have a negative impact on laying performance and egg quality.(2)VTG and VLDL are the primary composition of yolk precursor substances.The concentration of VTG and VLDL was affected by sound sources and stocking densities.The IML group(IMS+LD)had the highest concentration of VTG.VLDL in IMS and in LD treatments was higher,while the serum VLDL content of laying hens in MRS was significantly reduced.In terms of gene expression,we found there was an interaction between sound sources and stocking densities on the expression of vtgl and MTTP,both of which exhibit the highest expression levels in the NL group(NS+LD).Sound sources had significant effects on the expression of vtg2,vtg3,ApoB,CTSD,and VLDLR,and the expressions were significantly increased in IMS treatment.Stocking density had a significant main effect on the expression of vtg3,ApoB,and CTSD,and had a higher expression level in LD treatment.The expression of Apo V1 in the liver of green shell layers was not related to sound sources and stocking densities.Above-mentioned results indicate that instrumental sound sources and low stocking density are beneficial to yolk deposition,while mixed road noise and increased stocking densities are detrimental to yolk deposition.(3)There were no significant impact on serum GnRH content,while main effects of sound sources and stocking densities on serum LH and FSH content were showed.The concentration of LH and FSH in MRS treatment was decreased,while in LD treatment was increased.There was an interaction between the effects of sound sources and stocking densities on serum E2 and P4 content,mainly manifested by significantly lowest E2 and P4 levels in the MRH group(MRS+HD).In addition,in terms of sound sources,the expression of StAR,CYP11A1,and HSD3B1 genes in the ovaries of green shell layers in IMS treatment was higher,while the expression of CYP19A1 in MRS treatment was lower.In terms of stocking density,the expression of StAR in LD treatment was higher.These results reflect the promoting effects of instrumental music source and low stocking density on reproductive hormones and gene expression,and to some extent reflect the beneficial effects on production performance.On the contrary,the decrease in reproductive hormones and gene expression may also be the reason for the poor production performance of laying hens which kept under the condition of mixed road noise and high stocking density.(4)At the 1st d,there was an interaction between sound sources and stocking densities on the effects of ACTH and CORT concentrations.It showed that the MRL group(MRS+LD)exhibited the highest stress hormone levels.On the 3rd day,the sound source had a significant main effect,MRS treatment significantly increased the ACTH and CORT levels.While on the 12th and 24th days,a significant main effect was showed in stocking density,the ACTH and CORT levels were higher in HD treatment.At the 6th,12th,and 24th days of the trial,the frequency of drinking behavior of LD was higher,and the duration of LD treatment for drinking was longer at the 6th day.On the 6th day,the frequency of feeding behavior of HD was lower,and the duration of feeding behavior was also shorter on both 6th day and 12th day.On the 24th day of the trial,MRS treatment had the highest frequency of standing behavior,and on the 1st,3rd,6th,and 24th days of the trial,the duration of standing behavior in MRS treatment was longest.On the 1st and 3rd days of the trial,the frequency of standing behavior of LD was lowest,and the standing duration of LD treatment was also the shortest.On the 3rd day,there was an interaction between sound sources and stocking densities on the frequency of movement behavior,while sound source only affected the frequency of movement behavior of the 24th day,that is,the frequency of movement was highest in MRS treatment.At the 3rd,6th,12th,and 24th days,stocking density significantly affected the duration of movement behavior,and LD treatment had a higher duration of movement behavior.At the 3rd day,there was an interaction between the effects of sound sources and stocking densities on resting behavior.On the 1st,6th,12th,and 24th days,MRS treatment significantly reduced the frequency of resting behavior,while HD treatment significantly increased the frequency of resting behavior on the 12th day;MRS treatment significantly reduced the duration of resting behavior at days 12 and 24.On the 3rd day of the experiment,there was also an interaction between the effects of sound sources and stocking densities on preening behavior.At different time in the experiment,IMS treatment significantly increased the frequency and duration of preening behavior,while MRS treatment was opposite.Except for the 3rd day,sound sources and stocking densities had an interaction on the frequency of pecking behavior,while on the 6th day,the two factors had an interaction on the duration of pecking behavior.IMS groups significantly reduced pecking behavior,MRS groups significantly increased pecking behavior,LD groups significantly reduced pecking frequency,and HD groups significantly increased pecking duration.Overall,mixed road noise and high stocking density significantly increase the stress level and pecking behavior of green shell layers,while instrumental music and low stocking density are related to increased preening behavior and reduced pecking behavior.(5)Sound sources and stocking densities significantly affected the composition and structure of cecum flora in green shell layers.The Shannon index and Simpson index of green shell layers significantly decreased in IMS treatment.As for the Beta diversity,cecal bacterial communities tended to separate in response to different sound sources.At the phylum level,the proportion of Firmicutes in MRS treatment significantly decreased,while in LD treatment was significantly increased.At the genus level,IMS-exposed group significantly enriched Lactobacillus and Ruminococcus torques group,while MRS treatment significantly enriched Bacteroides and Parabacteroides.Stocking densities had no significant impact on the Alpha diversity and Beta diversity of green shell layers,but LD treatment significantly enriched Faecalibacterium and Megamonas at the genus level.In general,sound sources have a more significant impact on intestinal microflora.Lactobacillus which was enriched in instrumental sound sources,as a common beneficial microflora,may provide a healthier intestinal environment for laying hens.To sum up,sound sources and stocking densities have an impact on the production performance and health status of green shell layers.Instrumental sound source and low stocking density may have beneficial effects on egg production performance and egg quality of layers through yolk deposition and HPG axis regulation,thereby improving their production efficiency.In addition,these two factors also have advantages in reducing animal stress levels and improving their behavior.Moreover,the enrichment of beneficial bacteria in the intestines of green shell laying hens which exposed to music may ensure the health of animals,which is more conducive to providing humans with higher quality products.