Effects Of Oregano Essential Oil As Potential Alternative For Monensin On Ruminal Function And Growth Performance Of Young Holstein Dairy Bulls

In order to investigate the effect of oregano essential oil（OEO）as potential alternative for antibiotics.Male Holstein calves as the research object were used in this study at 70 days of age.The effects of OEO,Monensin（MON）,and their mixture on rumen function and growth of male dairy calves were systematically studied,in the aim to provide a theoretical basis for OEO replace of MON in animal husbandry to achieve non-Antibiotic breeding.Twelve Holstein dairy calves were randomly divided into four groups（three in each group）with the same genetic background,similar body weight（kg）,and in good physical condition,calves were fed from 70 to 310 days of age with the duration of the trial was 240 days.The experiment was a two-factor factorial,complete randomized design:1)CON（basal diet）;2)OEO（basal diet+26 mg/kg DM oregano essential oil）;MON（diet+25mg/kg DM monensin）;and mix of OEO and MON（basal diet+26 mg/kg DM oregano essential oil+25 mg/kg DM monensin）.In this study,we first analyzed the influence of OEO and MON on rumen microflora by high-throughput sequencing,we then studied the influence of OEO and MON on rumen fermentation parameters and microbial enzyme activity.According to the influence of OEO and MON on serum indices,combined with microflora,rumen fermentation parameters and microbial enzyme activities to reveal the main factors that caused the difference in growth performance of young Holstein dairy bulls.The main results are as follows:Trial one:Effects of dietary OEO and MON on rumen microflora of young Holstein dairy bulls.The effects of OEO and MON and their mixture on rumen microflora of dairy bulls were analyzed by 16S rDNA high through-put sequencing at different developmental stages.The results show that:1)At the phylum level,OEO and MON had significant interaction effects on Firmicutes,Spirochaetes,Fibrobacteres,and Synergistes from 70 to 190 days of age（P≤0.05）;The main effect of MON significantly increased the relative abundance of Proteobacteria（P<0.05）,and the relative abundance of Actinobacteria was highly significantly increased in rumen（P<0.01）.OEO and MON had a highly significant interaction effect on the relative abundance of Proteobacteria（P<0.01）,OEO and MON had a significant interaction effect on Actinonobacteria in rumen from 191 to 310 days of age（P<0.05）;The main effect of OEO significantly increased the relative abundance of Firmicutes and Spirochaetes in rumen（P<0.05）,and the relative abundance of Bacteroidetes was highly significantly decreased（P<0.01）;the relative abundance of Bacteroidetes and Fibrobacteres in the rumen were highly significantly increased in MON group（P<0.01）,and the relative abundance of Firmicutes was highly significantly decreased（P<0.01）.2)At the family level,there was a significant interaction between OEO and MON on the relative abundance of Veillonellaceae,Clostridiaceae,Christensenellaceae,Fibrobacteraceae,Spirochaetaceae,and Coriobacteriaceae（P<0.05）in rumen,OEO and MON had a highly significant interaction effect on Porphyromonadaceae from 70 to 190 days of age（P<0.01）;The main effect of MON significantly increased the relative abundance of Prevotellaceae and Succinivibrionaceae in the rumen（P<0.01）,and the relative abundance of Ruminococcaceae was highly significantly decreased（P<0.01）,and the relative abundance of Eubacteriaceae was significantly decreased（P<0.05）.there was a highly significant interaction between OEO and MON on the relative abundance of Porphyromonadaceae,Veillonellaceae,Christensenellaceae,and Succinivibrionaceae（P<0.01）,OEO and MON had significant interaction effects on Rikenellaceae and Fibrobacteraceae from 191 to 310 days of age（P<0.05）;In the main effects analysis,the relative abundance of Prevotellaceae in the rumen was highly significantly decreased in OEO group（P<0.01）,and the relative abundance of Lachnospiraceae,Spirochaetaceae,and others were significantly increased（P<0.05）;the relative abundance of Prevotellaceae was highly significantly increased in MON group（P<0.01）,the relative abundance of Ruminococceae was highly significantly decreased（P<0.01）,and the relative abundance of Eubacteriaceae,Clostridiaceae,and others were significantly decreased（P<0.05）.3)At the genus level,OEO and MON had significant interaction effects on the relative abundance of Paraprevotella、Ruminococcus,and Saccharofermentans in rumen from 70 to 190 days of age（P<0.05）,and there was a highly significant interaction between OEO and MON on the relative abundance of Acetivibrio（P<0.01）.The main effect of OEO significantly decreased the relative abundance of Lachnospiraceae_NA（P<0.05）,the relative abundance of Prevotella was highly significantly increased in MON group（P<0.01）,there were highly significantly decreased the relative abundance of Ruminococcaceae_NA and Eubacterium（P<0.01）,and the relative abundance of Porphyromonadaceae_NA was significantly decreased（P<0.05）.OEO and MON had significant interaction effects on the relative abundance of Porphyromonadaceae_NA and Saccharofermentans（P<0.05）,and there was a highly significant interaction between OEO and MON on the relative abundance of Paraprevotella（P<0.01）.In the main effects analysis,the relative abundance of Prevotella in the rumen was highly significantly decreased in OEO group（P<0.01）,the relative abundance of Lachnospiraceae_NA was highly significantly increased（P<0.01）,and the relative abundance of Ruminococcaceae_NA,Butyrivibrio,and others were significantly increased（P<0.05）;In the main effects analysis,the relative abundance of Prevotella was highly significantly increased in MON group（P<0.01）,the relative abundance of Ruminococcaceae_NA and Eubacterium were highly significant decreased（P<0.01）,and there was a significant reduction in Rikenella（P<0.05）.Trial two:Effects of dietary OEO and MON on rumen fermentation parameters and microbial enzyme activity of young Holstein dairy bulls.1)For interaction analysis,dietary supplementation just with OEO significantly increased the percentage concentration of propionate in the rumen,and there was a significantly decreased A/P value from 70 to 190 days of age（P≤0.05）;dietary supplementation just with MON significantly increased the percentage concentration of propionate（P<0.05）,decreased A/P value,and percentage concentration of butyrate,OEO and MON had significant interaction effects on the concentration of propionate,butyrate,Isobutyrate,and A/P value（P<0.05）.The main effect of OEO significantly increased the percentage concentration of isovalerate（P≤0.05）;MON significantly decreased the concentration of TVFA and acetate（P<0.05）.Dietary supplementation just with OEO or MON significantly increased the concentration of propionate and percentage concentration of propionate from 191 to 310 days of age（P≤0.05）,there was a significant interaction between OEO and MON（P<0.05）.The main effect of OEO or MON significantly decreased the concentration of NH₃-N（P<0.05）;MON significantly decreased the concentration of acetate and butyrate（P<0.01）,the concentraion of Isobutyrate was significantly decreased in MON group（P<0.05）.2)Effects of dietary OEO and MON on microbial enzyme activity in the rumen of young Holstein dairy bulls.For interaction analysis,dietary supplementation just with OEO significantly increased the activity ofα-amylase,cellulase,andβ-glucanase in the rumen from 70 to 190 days of age（P≤0.05）,dietary supplementation just with MON significantly increased the activity ofα-amylase（P≤0.05）,diet addition of mix of OEO and MON had a significant interaction（P<0.05）.The main effect of OEO significantly increased the activity of xylanase in the rumen（P<0.05）,MON significantly increased the activity of protease（P<0.05）.From 191 to 310 days of age,for interaction analysis,dietary supplementation just with OEO significantly decreased the activity of protease,OEO significantyly increasedα-amylase,cellulase,β-glucanase,CMC-ase,and xylanase in the rumen（P≤0.05）;dietary supplementation just with MON significantly increased the activity of protease,α-amylase,β-glucanase in the rumen（P≤0.05）,diet addition of mix of OEO and MON had significant interaction effects on protease,cellulase,β-glucanase,and xylanase（P<0.05）.Trial three:Effects of dietary OEO and MON on growth performance of young Holstein dairy bulls.The results show that:dietary supplementation just with OEO significantly increased the BW at 190 and 310 days of age,and BW gain from 70 to 310 days of age（P<0.05）,increased the ADG,DMI from 191 to 310 and70 to 310 days of age（P≤0.05）;dietary supplementation just with MON significantly increased BW at 190,310 days of age,and BW gain from70 to 190days of age（P≤0.05）,MON significantly increased ADG from 70 to 190 days of age（P≤0.05）,diet addition of mix of OEO and MON had a significantly interaction（P≤0.05）,antagonistic interactions were observed.Trial four:Effects of dietary OEO and MON on serum indices of young Holstein dairy bulls.The results show that:for the interaction analysis,dietary supplementation just with OEO significantly increased the concentration of TP in serum from 191 to 310 days of age,and 70 to 310 days of age（P≤0.05）,dietary supplementation just with OEO significantly increased the concentration of TG,diet addition of mix of OEO and MON had a significant interaction（P≤0.05）.The main effect of OEO significantly increased the concentration of SOD in serum from 70to190 days（P≤0.05）,OEO significantly increased the concentration of ALB from 70to 310 days of age（P≤0.05）.MON significantly decreased the concentration of BUN in serum（P≤0.05）.Overall,dietary supplementation with OEO has the potential to significantly affect rumen microbial community structure and function,rumen fermentation,can reduce the NH₃-N concentration of rumen,increase the concentration of propionate,improve growth performance,antioxidant and immune function.After comprehensive consideration,oregano essential oil can be considered as potential alternative for monensin in Holstein dairy bulls.