Temperature And Humidity Index (THI)induced Rumen Bacterial Community Changes In Goats

Climate change is one of the major threats to the sustainable survival of ecosystem and livestock production worldwide,and the thermoneutral zone is recognized as the appropriate temperature range for ruminants to regulate metabolism and physiology to normal levels.Oxidative damage to cellular and mitochondrial components is caused by excessive temperature and relative humidity.The temperature and humidity index?THI?is mainly used to reflect the intensity of heat stress in livestock.In recent years,most studies on heat stress have focused on monogastric animals or dairy cows.Boer goat is considered an ideal meat goat breed,whose production and reproductive performance are directly related to the temperature and humidity.Therefore it is also necessary to study the impact of heat stress on it.Rumen is a unique component of ruminants and contains a high density of microorganisms that play an important role in maintaining normal digestion and absorption of the host.High-throughput sequencing is a new detection technology that has emerged in recent years,and deep sequencing can obtain bioinformation about microbial communities via effective spatial and temporal views.PICRUSt,an approach that requires only 16 S rRNA gene?rDNA?sequences without the entire genome,was used to predict microbial function.Therefore,techniques such as 16 S rDNA sequencing were used to explore the adverse effects of heat stress on rumen pH,volatile fatty acid?VFA?and microbiome.Eight healthy female goats?Boer goat × Guangzhong dairy goat,aged 18 months,32.8 ± 3.4 kg?were randomly allocated into two groups and housed in control metabolic chambers A and B?the chambers were established in Northwest A & F University Experimental Station,Yangling,Shaanxi,China,and the temperature and RH automatically were precisely controlled with a precision deviation of ± 0.5°C and ± 5%,with 4 goats/chamber?.Goats from both chambers initially received an appropriate temperature and RH of 23°C and 50%?30 days to adapt to the chamber environment?.On day 30,goats in chamber A were treated as the control check?CK?.Then,different temperatures?26°C,30°C,34°C,38°C?and RHs?35%,50%,65%,80%?were set via completely randomized design;therefore,16 THIs were calculated,with each treatment lasting 5 days,and there was no time interval among each treatment.Rumen fluid samples were collected by oral intubation.After detecting pH,five milliliters of each sample was separated and stored at-20°C to assess VFA.After extracting DNA from the other samples,some was used to detect rumen microbial content by quantitative real-time PCR?qPCR?,and the dynamic changes of rumen bacterialcommunity under 16 gradually increasing temperature and humidity indexes?TH1^TH16?were detected by high-throughput sequencing technology.The results showed:?1?Heat stress significantly increased the pH,acetate and acetate/ propionate?P < 0.05?and reduced the total VFA,butyrate,valerate?P < 0.05?.However,the effect on propionate,isobutyrate and isovalerate is not significant;?2?qPCR revealed that heat stress significantly changed protozoa,methanogenic archaea,Fibrobacter succinogenes and Ruminococcus flavefaciens,but had no significant effect on total bacteria.?3?The changes of external temperature and humidity had no significant effect on the rumen bacterial community of goats?Ace,Chao 1,Shannon,Simpson,etc.?,but significantly changed the main phyla and genera of the rumen of goats.As THI increased,the relative abundance of Firmicutes decreased?from 67.09% to 27.21%?but Bacteroidetes increased?from 19.41% to 65.55%?,there was a negative correlation between the two phyla.At the genus level,the relative abundance of Prevotella₁ dominated in almost all groups,and was especially enriched in the high THI groups.With the increase of THI,some probiotics decreased and the abundance of pathogenic bacteria increased.Besides,the clusters between the TH group and the CK group were different.High TH group and low TH group were clustered respectively.In addition,the rumen bacterial community changed significantly from TH7 to TH9?THI from 80.61 to 82.92?.?4?PICRUSt was used to predict bacterial function.The results showed that significant changes in carbohydrate and energy metabolism with the increasing THI?P < 0.05?.By correlating the phyla with the metabolic pathway,we found that the relative abundance of Firmicutes was negatively correlated with amino sugar and nucleotide sugar metabolism?r =-0.432,P < 0.01?.The relative abundance of Bacteroidetes was positively correlated with purine metabolism?r = 0.412,P < 0.01?,but negatively correlated with ABC transporter?r =-0.455,P < 0.01?and aminoacyl-tRNA biosynthesis?r =-0.417,P < 0.01?.In summary,changes in THI could significantly affect goat pH,VFA,rumen microbial species and diversity.Some correlations were existed among different indicators.The pathogenic bacteria of the rumen of the goat increased and probiotics reduced with the increasing of THI.Moreover,the bacterial composition changes greatly when the THI increased from 80.61 to 82.92.