| Energy is the basic material of animal life activities.Dietary energy level has an impact on the digestion and absorption of nutrients and the composition and function of rumen microorganisms in sheep.Rumen microorganisms are closely related to energy metabolism and protein metabolism of sheep.The stability of rumen environment and the balance of rumen flora are the key to ensure the health and production efficiency of sheep.In this study,the effects of dietary energy level on nutrient digestion and absorption,rumen development and rumen microorganisms of 2-5 months old Soffolk×Hu F1 Generation Lambs were studied by adjusting the dietary energy level.Thirty-six 2-month-old white Suffolk sheep(♂)× Hu sheep(♀)F1 crossbred lambs with an average body weight of(20.58±1.47)kg were randomly divided into 3 treatment with 12 sheep in each treatment,with different dietary energy levels: 8.67 MJ/kg(LE),10.38MJ/kg(CON)and 12.31 MJ/kg(HE).The trial pre-trial period is 8 days,and the formal period is 70 days.On the 63 th day of the experimental period,three sheep was randomly selected from each treatment group for the digestion and metabolism test.All feces and urine were collected and weighed before morning feeding.After the experimental period,5 sheep were randomly selected from each treatment group,the rumen abdominal sacs were taken to measure their morphology,and the rumen fluid was extracted to measure their fermentation parameters and metagenomic sequencing.The experimental results are as follows:1,The decrease of dietary energy level significantly reduced dry matter digestibility,total energy digestibility and total energy utilization(P<0.05).Nitrogen intake decreased significantly with the increase of energy level(P<0.05),and there was no significant difference in apparent digestibility of nitrogen(P>0.05).Under the experimental conditions,high energy level diet can improve feed conversion efficiency and obtain higher production benefits.2,The decrease of dietary energy level significantly reduced the length of rumen nipple and inhibited the development of rumen nipple.High energy diet significantly increased microbial protein synthesis and butyric acid concentration(P<0.01).Dietary energy level had a significant effect on the concentration of volatile acids such as acetic acid,propionic acid,isobutyric acid,valeric acid and isovaleric acid in rumen(P<0.05).Dietary energy level affects rumen development and fermentation characteristics.3,The effects of dietary energy level on rumen microbial structure and function of sheep were studied.The results showed that:(1)ACE and Chao1 index of LE and CON groups were significantly higher(P<0.01)than that of HE group.At the genus level,the relative abundance of unclassified Lachnospiraceae in HE group was significantly higher than that in LE group(P<0.05),while the relative abundance of unclassified Bacteroides and Bacteroides in LE group and CON group was significantly higher than that in HE group(P<0.05,P<0.01),and the relative abundance of unclassified unclassified Rikenellaceae in HE group was significantly lower than that in CON group(P<0.05).At the level of species,the relative abundance of Rikenellaceae＿bacterium in HE group was significantly lower than that in CON group(P<0.05),while the relative abundance of Bacteroidales＿bacterium in HE group was significantly higher than that in LE group(P<0.05),and the relative abundance of Bacteroidales＿bacterium in he group was significantly lower than that in CON group(P<0.05)and LE group(P<0.01).The increase of dietary energy level significantly reduced the abundance of rumen microbial community and changed the structure of rumen microorganisms.(2)Enrichment of KEGG Level 3 pathway,Phosphotransferase system(PTS),Primary bile acid biosynthesis,Secondary bile acid biosynthesis,Geraniol degradation were significantly increased(P<0.05)with sheep energy intake elevating,while Glycosaminoglycan degradation,Various types of n-glycan biosynthesis,Glycosphingolipid biosynthesis-ganglio series,Renin-angiotensin system,Steroid hormone biosynthesis and Dioxin degradation were significantly decreased(P<0.05).High energy level diet significantly increased the gene abundance of enzymes such as GT2＿Glycos＿transf＿2,GH77,CE2,GT28(P<0.05)and decreased the abundance of GH31,GH92,GH20,CE15,GH9,GH146,CE15,GH13-6,GH43-29,CE6,GH8(P<0.05).Dietary energy level changes the activity of carbohydrate enzymes by changing the structure of rumen microorganisms,and changes the related pathways of microbial energy metabolism.(3)The results of correlation analysis showed that Successiclasticum＿ruminis was positively correlated with propionic concentration(P<0.01),Prevotella＿brevis was positively correlated with acetic concentration(P<0.05),Prevotellaceae＿bacterium was positively correlated with propionic,isobutyric and isovaleric(P<0.01).Lachnospiraceae＿bacterium was negatively correlated with ammonia nitrogen concentration and propionic concentration(P<0.05).In conclusion,the dietary energy level affects the digestion and absorption of nutrients and the development of rumen nipples,and changes the rumen fermentation characteristics and the composition and function of rumen microorganisms.High energy level diet can improve the feed utilization efficiency of sheep and obtain higher production efficiency.The dietary energy level of 12.31 MJ/kg can be applied to the fattening production of 2-5 month old Soffolk×Hu F1 Generation Lambs aged 2-5 months. |
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