Effect And Mechanism Of Niacin On The Performance And Rumen Function Of Heatstressed Beef Cattle

This experiment investigated the effects of niacin on the growth performance,nutrient digestibility,rumen fermentation,rumen epithelial barrier function,rumen microbial diversity,and rumen fluid metabolism of heat stressed beef cattle by adding niacin to the diet.The aim was to explore the effect and mechanism of niacin on the rumen function of heat stressed beef cattle,and to provide a theoretical basis for niacin to alleviate heat stress in beef cattle.36 healthy Jinjiang cows weighing 400 ± 20.0 kg were selected for feeding experiments and randomly divided into 3 treatment groups,each containing 4 replicates,with 3 cows per replicate.The three groups were the moderate temperature group(TN;temperature: 24-25 ℃,humidity: 45-55%),the heat stress group(HS;exposure to heat stress environment,average THI: 82.74),and the heat stress plus niacin group(HN;heat stress+800 mg/kg NA).The test results are as follows:Chapter 1: The effect of niacin on the production performance and rumen fermentation function of heat stressed beef cattle1)Compared with the TN group,the HS group significantly or extremely significantly increased the rectal temperature and respiratory rate of beef cattle(P < 0.05 or P < 0.01);Compared with the HS group,the HN group significantly reduced the rectal temperature and respiratory rate of beef cattle(P < 0.05).2)Compared with the TN group,the HS group had a tendency to reduce the average daily weight gain of beef cattle(P < 0.10),and at the same time had a tendency to increase the feed-to-weight ratio(P < 0.10);compared with the HS group,the HN group slightly increased the average daily weight gain of beef cattle(P > 0.05).3)There was no significant difference in nutrient digestibility between the TN and HS groups(P > 0.05);there was no significant difference in nutrient digestibility between the HS and HN groups(P > 0.05).4)Compared with the TN group,the HS group significantly reduced rumen p H and butyric acid content in beef cattle(P < 0.05),and highly significantly reduced acetic acid and total volatile fatty acid content(P < 0.01),with a tendency to reduce microbial protein concentration(P < 0.10);compared with the HS group,the HN group had a tendency to reduce the acetic acid/propionic acid ratio(P < 0.10).Chapter 2: Effect of niacin on rumen epithelial barrier function in heat-stressed beef cattle1)On days 30 and 45 of the experiment,the plasma levels of D-lactic acid in beef cattle in the HS group were significantly or highly significantly increased(P < 0.05 or P <0.01).On day 30,the HS group significantly increased the DAO concentration(P < 0.05).On days 30 and 45 of the experiment,the HS group significantly or highly significantly increased the concentration of LPS(P < 0.05 or P < 0.01);on day 45 of the experiment,the HN group had a tendency to reduce plasma D-lactate in heat-stressed beef cattle(P < 0.10),and on day 30 of the experiment,the addition of niacin significantly reduced the concentration of LPS(P < 0.05).2)Plasma concentrations of inflammatory cytokines IL-1β,IL-2,IL-6 and TNF-αwere significantly or highly significantly increased(P < 0.05 or P < 0.01)and concentrations of IL-4 were significantly or highly significantly decreased(P < 0.05 or P <0.01)in the HS group;plasma concentrations of inflammatory cytokines IL-1β,IL-2,IL-6and TNF-α in beef cattle in the HN group decreased significantly(P < 0.05)and the concentration of IL-4 increased significantly or highly significantly(P < 0.05 or P < 0.01).3)The m RNA expressions of tight junction proteins ZO-1,Claudin-1,Claudin-4 and Claudin-7 were significantly lower in the HS group than in the TN group(P < 0.05),and the m RNA expressions of ZO-1 and Occludin were significantly higher in the HN group than in the HS group(P < 0.05).There was no significant difference in ruminal RH and RW between the groups(P > 0.05).Chapter 3: Effect of niacin on rumen flora of heat-stressed beef cattle1)The microbial diversity results showed that the alpha diversity of the HS group was significantly lower than that of the TN group.At the phylum level,the relative abundance of the phylum Desulfobacterota in the HS group increased significantly(P < 0.05),and at the genus level,the genus Desulfovibrio in the HS group increased highly significantly(P< 0.01);the alpha diversity of the HN group was significantly higher than that of the HS group,and the relative abundance of the phylum Desulfobacterota in the HN group decreased significantly(P < 0.05)at the phylum level,and at the genus level,the The relative abundance of Succiniclasticum and Family＿XIII＿AD301 increased significantly(P< 0.05)and the relative abundance of Desulfovibrio decreased significantly(P < 0.05)in the HN group at the genus level.Chapter 4: Effect of niacin on rumen metabolomics in heat-stressed beef cattle1)The metabolomic results showed that there were 42 different metabolites in HS and TN groups,and they were mainly fatty substances and enriched 16 metabolic pathways;there were 9 different metabolites in HN and HS groups and enriched 4 metabolic pathways such as choline metabolism,linoleic acid,glycerophospholipid metabolism and purine metabolism in cancer.In conclusion,niacin can improve rumen barrier function,regulate rumen microflora,metabolites and pathways of heat stressed beef cattle,thereby changing the internal environment of the rumen,improving rumen fermentation function,improving the production performance of heat stressed beef cattle,and finally achieving the purpose of alleviating heat stress of beef cattle,providing a theoretical basis for niacin in the actual production of heat stressed beef cattle.