Effect Of Urea Supplementation On Growth Performance,rumen Fermentation And Ruminal Bacterial Community In Fattening Lambs

Urea,a non-protein nitrogen feedstuff,is high in nitrogen content but low in price.Urea is widely used in the current intensive ruminant production.However,when the amount of supplemental urea exceeds the maximum capacity of assimilation by ruminants,it can decrease animal performance and even cause ammonia toxicity.Therefore,this study was conducted to investigate the effects of urea supplementation on rumen fermentation,ruminal bacterial community and health in fattening lambs through in vitro and in vivo experiments.This study is divided into three parts.1 Effects of urea on in vitro fermentation and ruminal bacterial community.This study was conducted to evaluate the effects of urea on in vitro fermentation and composition of ruminal bacterial community.Urea was added to in vitro ruminal cultures at 4 doses:0(U0 group),24(U24 group),96(U96 group),384(U384 group)mg/dL.Each treatment contained 4 replicates.Ammonia concentration of UO group was lower(P<0.01)than U24 group.However,ammonia concentration of U384 group was higher(P<0.01)than U24 group.Compared with the U24,the gas production of the U96 group and U384 group were significantly reduced(P<0.01).The gas production of the UO group was numerically lower(P>0.05)than U24 group.The pH and ammonia concentration increased(P<0.01)with the increasing of urea addition.Moreover,the dry matter degradability and the concentration of acetic acid,propionic acid and total volatile acid showed a trend of increasing first and then decreasing,with the U24 group resulting in the highest.The populations of methanogens,fungi,protozoa,and total bacteria of U24 group were higher(P<0.01)than U384 group,but similar(P>0.05)to the UO group and U96 group.The relative abundance of Bacteroidetes,Proteobacteria and Fibrobacteres in the U384 group were lower(P<0.05)than other groups,while the relative abundance of Firmicutes was higher(P<0.05)than other groups.Overall,when the ammonia nitrogen concentration(U0 group)is too low,it will inhibit the fermentation.However,when the added amount of urea is 384 mg/dL,it will improve ammonia concentration,change the ruminal bacterial community structure and reduce the functional microbial population.These ultimately inhibit microbial in vitro fermentation.2 Effects of urea on growth performance,nutrient digestion,and plasma metabolites in fattening lambs.This study investigated the effects of urea on growth performance,nutrient digestion,and plasma metabolites in fattening lambs.Seventy fattening male lambs(24.3± 1.7 kg)sorted into 2 blocks according to body weight(BW)and assigned to 1 of 5 dietary treatments in a randomized block design.The five treatment diets were differing in nitrogen:SBM at 170 g/kg dry matter(SBM group)or reduced SBM(40 g/kg DM)plus 0(U0 group),10(U10 group),20(U20 group),or 30(U30 group)g urea/kg DM.The final BW,DM intake(DMI),average daily gain(ADG),and gain efficiency were similar(P≥0.42)between the SBM group and the urea-supplemented groups.However,the DMI and ADG increased quadratically(P<0.03)with the increasing urea addition to the diet,with lambs receiving the 10 g urea/kg DM diet has the highest.Linear and quadratic effects(P<0.01)on the crude protein(CP)intake and digestibility were observed with the increasing urea addition to the diet.The concentrations of plasma ammonia and blood urea nitrogen(BUN)increased(linear,P<0.05;quadratic,P<0.05)with the increasing urea supplementation.However,the levels of plasma metabolites were within or close to the normal range for healthy sheep.Overall,adding 10 g/kg DM urea is most suitable,which can improve the growth performance and nutrient digestibility of fattening Hu sheep to a certain extent.Moreover,adding 30 g/kg DM urea did not cause ammonia toxicity,and had no adverse effect on animal health.3 Effects of urea on rumen fermentation and the composition of ruminal fermentation and bacterial community in fattening Hu lambs.Based on the second chapter,this chapter was mainly conducted to evaluate the effect of urea supplementation on rumen fermentation and the composition of ruminal bacterial community in fatting Hu lambs.The results showed that,the ruminal pH and ammonia concentration of the U30 group was higher(P<0.05)than the U0 and U10 group.However,no difference(P≥0.05)was detected on ruminal concentrations of total VFAs,acetate,propionate or valerate among all the dietary treatments.The populations of total bacteria,methanogens,and protozoa of the U10 and U20 group were higher(P<0.05)than the U0 and U30 group,but they were similar(P>0.05)to the SBM group.Shannon index of U30 group was higher(P<0.05)than U0 group and U10 group,but there was no significant difference(P>0.05)between other groups.The bacterial community composition was separated of the U0,U10 group and the U20,U30 group by the principal coordinate analysis.The relative abundance of Bacteroidetes of U10 group was higher(P<0.05)than other groups,while the relative abundance of Firmicutes was lower(P<0.05)than SBM,U20 and U30 group.In conclusion,the rumen pH and ammonia concentration increased with addition of the urea.Meanwhile,the number of microorganisms in the rumen decreased.When the level of urea supplementation is too high,it will reduce the functional microbial population,and change the ruminal bacterial community structure.In conclusion,different levels of urea addition changed the ruminal pH and ammonia concentration,which affected the functional microbial population and the bacterial community structure.Appropriate urea addition level can increase the functional microbial population and improve rumen fermentation.However,high urea supplementation will increase the rumen pH and ammonia concentration,reduce the functional microbial population,and change the bacterial community structure,which lead to the inhibition of rumen microbial fermentation.