The kinetics of fibre digestion, nutrient digestibility and nitrogen utilization of low quality roughages as influenced by supplementation with urea-mineral blocks

摘要

Threeyearlinglambseachequippedwitharumencannulawereusedtostudytheeffectsofsupplementationwithaureaminerallickblock(ULB)onthekineticsofruminalfibredigestion,nutrientdigestibilityandnitrogen(N)utilizationofricestraw(RS),ammoniabicarbonate-treatedRS(ABRS)andhaypreparedfromnaturalpasture.ThedigestibilityofdrymatterandorganicmatterofRSwasincreasedby13.1and12.7%(P0.05)andapproachedtothatofABRS,indicatingthattheeffectofULBondigestibilityofRSissimilartothatoftreatmentwithAB.ThedigestibilityofABRSwasimprovedslightlybyULBfeeding.NitrogenretentionwashighestinlambsonABRSalone,followedbyhaywithULB,andwaslowestinanimalsonRSwithULB.HoweverbothamountofNretentionandproportiontointakewereincreasedbyULBsupplementationinlambsfedonhay.TheproportionofNretainedtoNdigesteddecreasedbyULBsupplementationinlambsonRSorABRS.Blockdidnotgreatlyinfluencetherumendegradationofeitherdrymatterorcrudeproteininanyoftheallthreediets.TheRSandhayhadsimilarvaluesforthepotentialextentofdigestion(PED)anddigestionrateofPED(kd)offibrousmaterials,butthediscretelagtimeforRSwaslowerthanthatforhay.TheABtreatmentincreasedthePED(P0.05)andkd(P.0.05)ofRS.NeitherthePEDnorkdforRSandABRSwasinfluencedbytheULBfeeding,butthekdforhaywasincreasedsignificantly.ThelagtimeforhaywasalsoshortenedbyULBfeeding.ULBimprovedthedigestionoffibreintherumenoflambsonlowqualityroughage.ItisinferredthatwhileULBiseffectiveinincreasingnutrientdigestibilityoflowqualityroughagesthroughtheimprovementinruminalfibredigestion,asynchronizedsupplyofNandenergytorumenmicrobesshouldbeconsideredtoimprovetheutilizationefficiencyofNwhenthebasaldietisammoniatedstraw.