| The stress caused by high stocking density has been restricting the development of broiler breeding,so it is of great significance for broiler production to find appropriate nutritional regulation strategies to alleviate the high feeding stocking density.As an important feed additive,acidifier can promote the growth of Broilers and improve the ability of antistress.Acidifier has the potential to alleviate the stress of high stocking density.We will test the growth performance,immune function,antioxidant function and intestinal function through two experiments to explore the effect of acidifier on the growth of broilers in the early stage and the alleviation of high stocking density stress in the later stage.Experiment 1: Effect of compound acidifier on broilers aged 0-21 days.480 0-day-old Arbor Acres(AA)broilers with similar body weight were randomly divided into acidifier group and control group,with 10 replicates per treatment and 24 broilers per replicate.The results showed that compared with the control group,in terms of growth performance,acidifier significantly reduced the feed to weight ratio(P<0.05).In terms of digestive function,acidifier increased the pancreatic index(P<0.01),the p H of contents in glandular stomach,muscular stomach and duodenum was significantly decreased.Acidifier significantly increased the activities of chymotrypsin and α-amylase in duodenal contents(P<0.05),but had no significant effect on trypsin and lipase(P>0.05).In terms of lipid metabolism regulation,acidifier significantly reduced serum triglyceride and low density lipoprotein levels(P<0.05),and significantly increased serum high density lipoprotein levels(P<0.05).In terms of inflammatory injury and stress regulation,acidifier significantly increased serum IgG,IL-1,IL-4,IL-6 and INF-γ levels(P<0.01),decreased serum IL-2(P<0.01)and serum cortisol levels(P<0.05).Drinking water type compound acidifier can improve feed conversion rate,pancreatic index,chymotrypsin andα-amylase activities of duodenal contents,reduce serum triglyceride and low density lipoprotein levels,improve high density lipoprotein,improve fat transport rate,and improve immune function by regulating immunoglobulin and cytokines.Experiment 2: The effect of compound acidifier on alleviating the high stocking density stress of 22-42 days old broilers.A 2 × 4 factorial design was used in the experiment.The experiment lasted for 22-42 days.Four density gradients were set on the basis of pretreatment(whether acidifier was added or not): 14 broilers/m~2,16 broilers/m~2,18 broilers/m~2 and 20broilers/m~2.There were 8 treatments with 6 replicates in each treatment,totally 816 Arbor Acres(AA)broilers.The results showed that:(1)In terms of growth performance and organ index:Compared with the 14 broilers/m~2 group,high stocking density significantly reduced the body weight,average daily gain,average daily feed intake(P<0.01)and thymus index(P<0.05)of broilers aged 42 days.Acidifier significantly decreased liver index(P<0.01)and increased thymus index(P<0.01).(2)In terms of digestive function: Acidifier significantly reduced the p H of glandular stomach,muscular stomach and duodenum contents(P<0.01).Acidifier significantly increased the activity of lipase and α Amylase activity(P<0.05),but there was no significant effect on trypsin and chymotrypsin activity.Acidifier significantly increased the utilization rate of dry matter,total phosphorus and calcium(P<0.05).20 broilers/m~2 group significantly reduced the utilization rate of crude fat(P<0.05).(3)In the regulation of lipid metabolism: Acidifier and feeding density had interaction effect on the level of glutamyltransferase(P<0.05).The serum glutamyltransferase activity was significantly increased in the group without acidifier in 20broilers/m~2 group(P<0.05),but the increase of serum glutamyltransferase level was reversed in the group with acidifier in 20 broilers/m~2 group(P<0.05).The serum cholesterol and high density lipoprotein levels were significantly increased(P<0.05)in the 16 broilers/m~2 group,and the serum high density lipoprotein level was significantly decreased by acidifier(P<0.05).(4)In the aspect of serum antioxidation: Acidifier significantly increased serum T-AOC,decreased serum MDA content and GSH-Px activity(P<0.05),increased GSH-Px activity in 20 broilers/m~2 group(P<0.05).(5)In terms of immune function: Acidifier and stocking density had significant interaction effects on serum IgA,IgG,IgM,IL-1,IL-2,IL-4,IL-6,IL-10,INF-γ,TNF-α and cortisol(P<0.01): Compared with the control group,the levels of IgA,IgG and IgM in 16broilers/m~2 group and 18 broilers/m~2 group were increased.Compared with the control group,adding acidifier increased the INF-γ of 14 broilers/m~2 group and 20 broilers/m~2 group,the level of TNF-γ was increased in 14 broilers/m~2 group and 18 broilers/m~2 group,the levels of cortisol in 14broilers/m~2 group and 16 broilers/m~2 group were decreased.Compared with the control group,adding acidifier increased IL-1 level in 16 broilers/m~2 group,decreased IL-2 level in 14broilers/m~2 group and 18 broilers/m~2 group,and decreased IL-6 level in 16 broilers/m~2 group.Compared with the control group,acidifier increased the level of IL-4 in 16 broilers/m~2 group,decreased the level of IL-4 in 18 broilers/m~2 group and 20 broilers/m~2 group,and decreased the level of IL-10 in 16 broilers/m~2 group and 18 broilers/m~2 group.(6)In terms of cecal volatile acid and cecal flora: Acidifier significantly increased the concentrations of acetic acid(P<0.05),butyric acid,valeric acid and isovaleric acid(P<0.01),16S rDNA analysis showed that acidifier and stocking density had no significant effect on α-diversity and β-diversity of cecal flora(P>0.05).Acidifier group could increase the relative abundance of Firmicutes,which play an important role in the growth and nutrient absorption of the body,Lachnospiraceae and Ruminococcaceae,which can secrete volatile fatty acid.High stocking density can reduce growth performance and thymus index of 22-42 days old broilers,reduce immune function and fat absorption and metabolism.Acidifier can improve immune function,fat synthesis rate,antioxidant function,nutrient utilization rate and cecal volatile fatty acid content(acetic acid,butyric acid,isovaleric acid and valeric acid)of 22-42 days old broilers.In conclusion,adding acidifier at the early growth stage can improve the production performance,and alleviate the stress caused by high stocking density by improving the body’s antioxidant,fat metabolism and enhancing immune function. |
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