| Yellow feather broilers are widely distributed in southern our country.It is famous for its unique and delicious meat taste.However,it takes a long time to feed,has a high coat rate,and has a poor breeding environment.It is prone to heat stress in summer and causes serious economic losses.As an important target of stress,the gut-brain axis is vulnerable to heat stress and affects the production performance of broilers in the middle and late stages.N,NDimethylglycine is an important compound in the choline metabolism pathway,which has important research significance for alleviating stress damage in poultry and repairing intestinal microorganism disorders.The purpose of this experiment is to investigate the mechanism of dietary supplementation of dimethylglycine on the intestinal barrier damage of broilers under heat stress based on the gut-brain axis.In this experiment,162 42-day-old male medium-speed "You Ma" yellow feather broilers with similar body weights were selected and randomly divided into 3 groups,each group with6 replicates,and each replicate with 9 broilers.The specific groups are named: normal temperature control group(fed basic diet),heat stress test group(fed basic diet),heat stress +dimethylglycine group(basic diet fed +0.1% DMG)(below referred to as the dimethylglycine group).The experiment was carried out in an animal nutrition and metabolic environment control chamber,and the temperature of the normal temperature control group was set to 26°C;the heat stress treatment group was subjected to gradual heating pre-feeding for 14 consecutive days,and then cyclic heat stress for 14 consecutive days.The production performance was calculated on the 14 th and 28 th days of the experiment,and a test chicken with a similar average weight was randomly selected from each replicate group on the 28 th day for weighing and slaughter.The test results show that: 1)Heat stress significantly reduces 1-14 d body weight,1-14 d average daily gain,1-14 d average daily food intake,28 d body weight,15-28 d average daily gain,and 15-28 d average daily food intake,1-28 d average daily gain,1-28 d average daily feed intake(P < 0.05),significantly increase 1-14 d,15-28 d,and 1-28 d F/G(P < 0.05);and compared with the heat stress test group,the dimethylglycine group significantly increased15-28 d average daily gain(P < 0.05);significantly reduced the 15-28 d F/G(P < 0.05);has a tendency to increase 28 d body weight(P = 0.060),1-28 d average daily gain(P = 0.057);has a tendency to decrease 1-28 d F/G(P = 0.081).2)Compared with the control group,heat stress group significantly increases the crypts depth of jejunal,and significantly reduces the villus length of duodenal,the duodenal villus/crypts ratio(V/C)value,the thickness of the duodenal mucus layer,and the duodenal muscle thickness,jejunum V/C value,jejunum mucus layer thickness,ileum villi length,ileum muscle thickness(P < 0.05);the dimethylglycine group significantly increased the jejunum V/C value than the heat stress test group(P < 0.05),there was a tendency to increase the V/C value of the duodenum(P = 0.073),to increase the thickness of the duodenal mucus layer(P = 0.054),and to significantly reduce the depth of the jejunal crypt(P < 0.05).3)Heat stress significantly reduced the number of goblet cells in jejunum and increased the number of goblet cells in ileum(P < 0.05);compared with the heat stress group,the number of goblet cells in jejunum of dimethylglycine group was significantly increased(P< 0.05).4)Compared with the control group,the heat stress test group significantly increased the expression of zonule atresia protein 1(ZO-1)in the jejunal mucosa(P < 0.05),and there was a tendency to increased the expression of the seal protein 1(Claudin1)gene(P = 0.084),significantly reduced the gene expression of mucin 2(MUC-2)(P < 0.05);compared with the heat stress test group,the dimethylglycine group significantly increased the gene expression of MUC-2(P < 0.05),had a tendency to increase the expression of Claudin1(P = 0.052).5)Compared with control group,the heat stress test group significantly increased the tumor necrosis factor-α(TNF-α)content in the jejunal mucosa(P < 0.05),and increased the proinflammatory factor interleukin-6(IL-6)(P = 0.058),the trend of interleukin-8(IL-8)(P =0.088)content,the trend of reducing the content of anti-inflammatory factor interleukin-10(IL-10)(P = 0.080);compared with the heat stress test group,the dimethylglycine group has a tendency to decrease the content of IL-6(P = 0.090)and increase the content of IL-10(P =0.083)At the m RNA level,the heat stress test group significantly increased the expression of IL-6,TNF-α,NF-κB1,and STAT3 genes in the jejunum mucosa compared with the control group(P < 0.05),and had a tendency to increase the expression of IL-8 gene(P = 0.096),there was a tendency to decrease the gene expression of IL-10(P = 0.062);compared with the heat stress test group,the dimethylglycine group significantly decreased the gene expression of IL-6,NF-κB1,and STAT3(P < 0.05).6)Compared with the control group,the heat stress test group significantly decrease the cecal microbial abundance of Romboutsia,Faecalibacterium,unidentified Ruminococcaceae,Phascolarctobacterium(P < 0.05),and decreased the genus level of Elusimicrobium(P = 0.096),Peptococcus(P = 0.090)),Candidatus Arthromitus(P =0.075),Bilophila(P = 0.092),Nitrosomonas(P = 0.082),Stenotrophomonas(P = 0.076)flora abundance trends;compared with the heat stress test group,the dimethylglycine group has a tendency to increase the abundance of the genus Methanocorpusculum(P = 0.073)and Marvinbryantia(P = 0.093),and decrease the abundance of Odoribacter(P = 0.076),Ruminiclostridium(P = 0.076),and Oxalobacter(P = 0.076).7)Compared with the control group,the heat stress test group significantly reduced the content of acetic acid,propionic acid,butyric acid,valeric acid,caproic acid,total short-chain fatty acids,total acetic acid and total valeric acid in the cecal chyme(P < 0.05);compared with the heat stress test group,the dimethylglycine group significantly increased the content of isobutyric acid in the cecum(P <0.05),increased acetic acid(P = 0.052),total short chain fatty acids(P = 0.066),and total valeric acid(P = 0.071).8)Compared with the control group,the heat stress test group significantly reduced the content of tryptophan and serotonin(5-HT)in the cecal chyme(P <0.05),and significantly increased the content of picolinic acid and quinolinic acid(P < 0.05).0.05);Compared with the heat stress test group,the dimethylglycine group significantly increased 5-hydroxy-L-tryptophan,kynurenine,5-HT content(P < 0.05),and had a tendency to increase tryptophan(P = 0.061),significantly reduced the content of picolinic acid(P < 0.05).It shows that dietary supplementation of dimethylglycine can alleviate the abnormal metabolism of short chain fatty acids and tryptophan by repairing the disturbance of intestinal flora caused by heat stress.9)The tryptophan metabolism in hypothalamus,we found that heat stress significantly reduces the content of kynuric(P < 0.05),has a tendency to reduce serotonin(P = 0.055),and significantly increases the content of quinolinic acid(P < 0.05);compared with the heat stress test group,the dimethylglycine group had a tendency to increase the content of 5-hydroxy-L-tryptophan(P = 0.089),kynurenic acid(P = 0.078),and serotonin(P = 0.070),significantly reduce the content of quinolinic acid(P < 0.05).At the m RNA level,the heat stress test group significantly decrease the gene expression of kynurenine aminotransferase(KAT)(P< 0.05)compared with the control group,and had a tendency to decrease the gene expression of tryptophan-2,3-dioxygenase(TDO)(P = 0.065),significantly increase kynurenine-3-monooxygenase(KMO)gene expression(P < 0.05);compared with the heat stress test group,the dimethylglycine group was significantly increase KAT gene expression,and significantly decrease KMO gene expression.10)The metabolism of monoamine neurotransmitters in the hypothalamus,we found that the heat stress test group significantly reduced the hypothalamic dopamine,glutamine,and 5-HT content(P < 0.05)compared with the control group(P < 0.05),and reduced demethylation adrenaline(P = 0.059);compared with the heat stress test group,the dimethylglycine group significantly increased the content of hypothalamic aminoamide and serotonin(P < 0.05),and there was a tendency to increase the content of glutamate(P = 0.065).In summary,adding 0.1% N,N-dimethylglycine to the diet can effectively alleviate the decrease in the production performance of medium speed "You Ma" yellow feather broilers caused by cyclic heat stress,and the mechanism of action may be dimethyl glycine promotes intestinal absorption through the nutrients in the emulsified feed or repairs the intestinal microorganism disorder caused by heat stress in the form of the carbon source of the intestinal microorganism,relieve the imbalance of short-chain fatty acid and tryptophan metabolism of cecal microbes through intestinal microorganism,which could increase the secretion of intestinal antiinflammatory factors,reduce the secretion of pro-inflammatory factors,and reduce the occurrence of intestinal inflammation.In addition,the two-way mechanism based on the intestine-brain axis affects the synthesis and release of tryptophan and monoamine neurotransmitters metabolism in the hypothalamus,further improving the body’s intestinal health.The results of this experiment provide a new idea and direction for the screening and research of anti-heat stress additives. |
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