| Since the ban on the use of antibiotics in feed in China,the risks of reduced animal survival rates,decreased productivity,and increased breeding costs in the livestock and poultry industries have been growing in the short term.Acidifiers,as a class of efficient,residue-free,and side-effectfree green feed additives,have a significant growth-promoting effect and are expected to solve this problem.This study used growing Sichuan white geese as experimental animals and explored the effects of adding citric acid to the diet on growth performance,blood indicators,intestinal health,and cecal microbial communities in growing Sichuan white geese.The main research results are as follows:1.Effects of dietary citric acid on growth performance,slaughter performance,and meat quality of growing Sichuan white geeseA total of 240 25-day-old Sichuan white geese were selected and randomly divided into 6 treatment groups according to the principle of no difference in initial body weight.Each treatment group had 5 replicates,with 8 geese per replicate.The different treatment groups were fed different levels of citric acid,namely 0.8%,1.6%,2.4%,3.2%,and 4%,with no citric acid added to the control group.All experimental geese were exposed to natural light,free feeding,and drinking water,with the pre-feeding period starting at 25 days of age and the main experimental period from 28 to 70 days of age.Feed consumption and body weight changes were recorded during the experiment,and average daily weight gain,average daily feed intake,and feed-to-weight ratio were calculated.At 70 days of age,a slaughter trial was conducted,and the weights of carcasses and various organs were recorded and slaughter performance and organ indices calculated.Breast muscle samples were collected to measure meat quality.The results showed that:(1)at 70 days of age,the body weight,average daily weight gain,and average daily feed intake of the 2.4%and 3.2%treatment groups were significantly higher than those of the control group,0.8%,1.6%,and 4%treatment groups(P<0.05);the differences in feed-to-weight ratios among the groups were not significant(P>0.05).(2)The leg muscle percentages of the 0.8%,1.6%,2.4%,and 4%treatment groups were significantly higher than those of the control group(P<0.05);the skin fat percentages of the 3.2%and 4%treatment groups were significantly lower than those of the control group(P<0.05);the abdominal fat percentages of the 0.8%,1.6%,2.4%,3.2%,and 4%treatment groups were significantly lower than those of the control group(P<0.05),while there were no significant differences among the groups in slaughter rate,net carcass rate,breast muscle percentage,heart index,liver index,and stomach index(P>0.05).(3)There were no significant differences in meat color L*,a*,and b*values,cooking loss,and shear force(P>0.05),but the pH of the 3.2%citric acid treatment group was significantly higher than that of the other groups(P<0.05);there were no significant differences in the moisture,ash,crude protein,crude fat,and amino acid content of goose breast muscle among the groups(P>0.05).2.Effects of dietary citric acid supplementation on blood biochemical,antioxidant,and hormone indicators in growing Sichuan White geeseThe experimental design was the same as Chapter 1.At 70 days of age,blood samples were collected from the wing vein of the geese in the morning on an empty stomach.The samples were centrifuged and stored at-80℃ for testing.Some samples were analyzed using an automatic biochemical analyzer for routine blood biochemical indicators,while others were measured using ELISA kits for antioxidant,immune,and hormone indicators.The results showed that:(1)Dietary citric acid supplementation significantly affected blood protein metabolism-related indicators.The 4%treatment group had significantly lower globulin and total protein levels than the 1.6%and 2.4%treatment groups(P<0.05),while there were no significant differences in albumin levels(P>0.05).The urea content in the 0.8%,1.6%,3.2%,and 4%treatment groups was significantly lower than that in the control group(P<0.05),and the uric acid content in the 1.6%,2.4%,3.2%,and 4%treatment groups was significantly lower than that in the control group(P<0.05),but there were no significant differences in creatinine content among the treatment groups(P>0.05).(2)Dietary citric acid supplementation did not affect blood glucose metabolism indicators.No significant differences were observed in glucose content and insulin activity among the treatment groups(P>0.05).(3)Dietary citric acid supplementation significantly affected blood lipid metabolism-related indicators.The 3.2%treatment group had significantly lower triglyceride and leptin levels than the control and 0.8%treatment groups(P<0.05),while the high-density lipoprotein level was significantly higher than that in the control,0.8%,and 2.4%treatment groups(P<0.05).Low-density lipoprotein levels tended to decrease as the level of citric acid supplementation increased(P=0.0542),and there were no significant differences in total cholesterol levels(P>0.05).(4)Blood calcium and total phosphorus were not affected by dietary citric acid supplementation(P>0.05).(5)Dietary citric acid supplementation can alleviate liver damage.The alanine aminotransferase activity in the 0.8%,1.6%,2.4%,3.2%,and 4%treatment groups was significantly lower than that in the control group(P<0.05);the aspartate aminotransferase activity in the 1.6%,2.4%,3.2%,and 4%treatment groups was significantly lower than that in the control group(P<0.05).(6)Dietary citric acid supplementation can improve the antioxidant level of the body.The glutathione peroxidase activity in the 3.2%treatment group was significantly higher than that in the 0.8%,1.6%,and 4%treatment groups(P<0.05).Total antioxidant capacity increased first and then decreased with the increasing level of citric acid supplementation(P=0.0914),with the highest in the 3.2%treatment group and the lowest in the 4%treatment group;no significant differences were observed in superoxide dismut mutase,malondialdehyde,and catalase activities among the treatment groups(P>0.05).(7)Dietary citric acid supplementation had no significant effect on blood immune indicators.No significant differences were observed in immunoglobulin A,immunoglobulin G,and immunoglobulin M levels among the treatment groups(P>0.05).(8)Dietary citric acid supplementation can promote the secretion of growth-promoting hormones.Insulin-like growth factor 1(IGF-1)in the 3.2%treatment group was significantly higher than that in the control and 4%treatment groups(P<0.05),while there were no significant differences in growth hormone levels(P>0.05).3.Effects of dietary citric acid supplementation on small intestine pH,morphology,and duodenal enzyme activity in growing Sichuan White geeseThe experimental design was the same as in Chapter 1.At the end of the experiment,samples were collected after slaughter,small intestine pH was measured,small intestine tissue was collected for observation of small intestine morphology,and villus height,crypt depth,and muscle layer thickness were measured and the villus-to-crypt ratio was calculated.Duodenal contents were collected to determine the activity of digestive enzymes by ELISA kits.The results showed that(1)dietary citric acid supplementation significantly reduced the pH and acid-binding capacity of the diet(P<0.05);(2)the pH of the jejunum in the 4%treatment group was significantly lower than that in the control group(P<0.05),while there were no significant differences in duodenal and ileal pH(P>0.05);(3)citric acid supplementation had no significant effect on villus height,crypt depth,and muscle layer thickness in the duodenum,jejunum,and ileum,but the villus-to-crypt ratio in the duodenum and jejunum tended to increase(0.05<P<0.10);(4)as the level of citric acid supplementation increased,the activity of lipase and chymotrypsin in the duodenum showed a trend of first increasing and then decreasing(0.05<P<0.10),reaching maximum values at 2.4%and 3%citric acid supplementation levels,respectively,while there were no significant effects on amylase and trypsin activity(P>0.05).4.Effects of dietary citric acid supplementation on the cecal microbial community of growing Sichuan White geeseThe control group and the 2.4%,3.2%and 4%treatment groups were selected according to the performance of growth performance,named C,T1,T2,and T3 group,and the cecum contents were collected to analyze the cecum microbial diversity and the composition and structure of the cecum microbiota.The results showed that:(1)the ACE and Chao1 indexes were significantly higher in the 2.4%treatment group than in the control and 3.2%treatment groups(P<0.05);(2)At the phylum level,Firmicutes,Bacteroidetes,Desulfobacterota and Actinobacteriota were the dominant phylum,and 3.2%and 4%citric acid addition levels significantly reduced the relative abundance of Patescibacteria(P<0.05),while 2.4%citric acid addition level significantly increased the relative abundance of Firmicutes(P<0.05);(3)At the genus level,Bacteroides,Desulfovibrio and Alistipes were the dominant genera,and 2.4%citric acid addition significantly increased the relative abundance of Candidatus_Soleaferrea(P<0.05)and unclassified_Burkholderiales(P<0.05)and significantly decreased the relative abundance of Bifidobacterium(P<0.05)and unclassified_Atopobiaceae(P<0.01);The 3.2%citric acid addition level significantly increased the relative abundance of Granulicatella(P<0.01)and Campylobacter(P<0.05),and decreased the relative abundance of Candidatus_Saccharimonas(P<0.01),Bifidobacterium(P<0.05),and unclassified_Atopobiaceae(P<0.01)and Streptococcus(P<0.05);4%citric acid addition level significantly increased the relative abundance of unclassified_Oscillospiraceae(P<0.05),uncultured Clostridia bacterium(P=0.072),uncultured Clostridiales b acterium(P<0.05),unclassified_Victivallaceae(P<0.05),Granulicatella(P<0.01),and Desulfovibrio(P=0.062)in relative abundance,reducing the relative abundance of unclassified_Atopobiaceae(P<0.01),Candidatus_Saccharimonas(P<0.01),Bacteroides(P<0.05),Buchnera(P<0.05),Subdoligranulum(P<0.05),Enorma(P<0.05)and Bifidobacterium(P<0.05).5.Effects of dietary citric acid supplementation on the hepatic transcriptomics of growing Sich uan white gooseLiver tissues were respectively collected from 5 geese in the control group,2.4%,3.2%and 4%citric acid treatment groups,named C,T1,T2,and T3 group.The effect of dietary citric acid addition on the liver metabolism of geese was investigated based on transcriptomic analysis.The results showed that the number of up-and down-regulated genes were 218 and 162 in group T1,91 and 126 in group T2,85 and 153 in group T3,respectively,compared with the control group.The GO enrichment results showed that the significant GO term in group T1 were mainly related to biological processes such as transferase activity,glutamate receptor,Wnt signaling pathway,cell surface receptor signaling pathway,and protein folding,compared with the control group;The significant GO term in group T2 were mainly related to defense response and enzyme inhibitor activity;the significant GO term in group T3 were mainly related to immune response,oxidoreductase activity,tumor necrosis factor receptor binding and other biological processes.The T2 group was significantly enriched for cell adhesion molecules and neuroactive ligand-receptor interactions,while the T3 group was significantly enriched for metabolic processes such as myocardial contraction,fatty acid prolongation,adrenergic signaling in cardiac myocytes,propionic acid metabolism,and unsaturated fatty acid biosynthesis.In conclusion,the addition of citric acid to the diet of Sichuan white goose during the growth period can improve the production and slaughter performance of the goose,affect the meat quality,improve lipid metabolism and protein metabolism,regulate hepatic transcription and alleviate liver damage,promote the secretion of IGF-1,improve the antioxidant capacity,lower the pH of the digestive tract,increase the activity of digestive enzymes,improve the morphology of the intestinal tract,increase the abundance of beneficial bacteria and thus maintain the intestinal health.Under the conditions of this experiment,the appropriate level of citric acid addition was 2.4%. |
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